The effects of ammonia-N stress on immune parameters, antioxidant capacity, digestive function, and intestinal microflora of Chinese mitten crab, Eriocheir sinensis, and the protective effect of dietary supplement of melatonin

Ammonia nitrogen pollution seriously affects the economic benefits of Chinese mitten crab (Eriocheir sinensis) farming. In this study, we first evaluated the protective effects of melatonin (MT) on immune parameters, antioxidant capacity, and digestive enzymes of E. sinensis under acute ammonia nitrogen stress. The results showed that ammonia-N stress significantly decreased the antibacterial ability of crabs, nevertheless MT could significantly improve it under ammonia-N stress (P < 0.05). Ammonia-N group hemolymph antioxidant capacity indicators (T-AOC, T-SOD, GSH-Px) were significantly decreased than control (p < 0.05), while the MT ammonia-N group hemolymph T-SOD activity significantly increased than ammonia-N group (p < 0.05). For hepatopancreas, ammonia-N group GSH-PX activity significantly decreased than control group, but MT ammonia-N group was significant increased than ammonia-N (p < 0.05). Ammonia-N stress has significantly increased the content of MDA in hemolymph and hepatopancreas (p < 0.05), but MT ammonia-N treatment significantly decreased than ammonia-N group (p < 0.05). Compared with the control group, ammonia-N significantly reduced the activities of Trypsin in the intestine and hepatopancreas (p < 0.05), while MT ammonia-N group can significantly improve the intestinal trypsin activity than ammonia-N (p < 0.05). The intestinal microbiota of E. sinensis results showed that ammonia-N stress significantly decreased the relative abundance of Bacteroidetes (p < 0.05). Ammonia-N stress significantly decreased the Dysgonomonas and Rubellimicrobium, and the Citrobacter significantly increased. In summary, melatonin has a protective effect on E. sinensis under ammonia-N stress. Acute ammonia-N stress may lead to the decrease of probiotics and the increase of pathogenic bacteria, which may be closely related to the impairment of digestive function and immune function.

Effect of size on concentrations and cadmium inducibility of metallothionein in the shore crab Carcinus maenas

Metallothionein (MT) plays an important role in protecting organisms from the adverse effects of Cd, Hg, Zn and Cu. Investigations on mammals show variations in metallothionein concentrations and inducibility with age. This has never been investigated in invertebrates, and we determined the concentrations and inducibility of metallothionein in gills and midgut gland of different size classes of shore crabs from uncontaminated areas. Metallothionein concentrations in gills and midgut gland ranged between 30 and 40 μg g^-1 dry weight with no differences among the different size classes. Concentrations of cadmium, copper and zinc in the midgut gland increased with increasing size of the crabs when the concentrations were expressed on a dry weight basis; water content in the midgut gland increased with the size and only the cadmium concentration increased with size when concentrations were expressed on wet weight basis. There was an inverse relationship between metallothionein and both copper and cadmium concentrations. Smaller crabs exposed to 1 mg Cd L^-1 accumulated higher concentrations of cadmium in midgut gland and gills than larger ones and metallothionein concentrations in the midgut gland were higher in the smaller crabs. However, the increase in metallothionein concentration per accumulated unit of cadmium showed a linear increase with the size of the crabs. The ratio [Cd]_midgut/[Cd]_gills decreased with the size of the crabs. The overall conclusion is that baseline metallothionein concentrations do not change with age in shore crabs, but that the inducibility of metallothionein upon cadmium challenge does.

Short communication: Effects of acute copper exposure on ionic regulation of the freshwater crab Aegla castro

Aeglids are unique freshwater decapods whose habitats are being impacted by metallic compounds, such as copper (Cu). Thus, we investigated the effects of acute Cu exposure on ionic regulation of Aegla castro. For this, male specimens in intermolt were collected from a reference stream and acclimated for 5 days in laboratory. After which, crabs were exposed to 11 μg L^-1 Cu (Cu11) or only to water (CTR) for 24 h. Hemolymph samples were withdrawn for the determination of Na⁺, K⁺, Ca²⁺, and Mg²⁺ concentrations and the posterior gills removed for the analysis of Na⁺/K⁺-ATPase, Ca²⁺-ATPase, H⁺-ATPase, and carbonic anhydrase (CA) activities. Increased Ca²⁺ and Mg²⁺ hemolymph concentrations were observed in animals from Cu11, when compared with CTR group. In addition, decreased activity of CA was observed in animals exposed to Cu. In the current study, alterations in Ca²⁺ and Mg²⁺concentrations probably indicate that animals activated exoskeleton reabsorption mechanisms, characteristic of the premolt. Therefore, increased Ca²⁺ and Mg²⁺ concentrations in hemolymph may indicate that a biochemical signal associated with the molting cycle was triggered by Cu exposure. Despite the known harmful effects of Cu on osmoregulatory enzymes, here we observed decreased activity only in CA. However, decreased activity of CA could trigger both acid-base imbalance and ionic disruption, since CA provides H⁺ and HCO₃^- for intracellular pH maintenance, and underpins Na⁺ and Cl^- for ionic regulation. Therefore, understanding how aeglids respond to metal contamination in laboratory conditions is crucial to assess their potential as an alternative biological model for aquatic ecotoxicology.

β-1,3-Glucan from Euglena gracilis as an immunostimulant mediates the antiparasitic effect against Mesanophrys sp. on hemocytes in marine swimming crab (Portunus trituberculatus)

β-1,3-glucans, natural polysaccharide groups, exert immunomodulatory effects to improve the innate response and disease resistance in aquatic species and mammals. However, this β-glucan stimulant is yet to be assayed in swimming crab (Portunus trituberculatus) hemocytes. In this study, we explored the immunomodulatory effect of β-1,3-glucans (derived from Euglena gracilis) via in vitro 24 h stimulation assays in swimming crab hemocytes. We found that this algal β-1,3-glucans in crab hemocytes significantly elevated cellular enzymes related parameters, including phenoloxidase (PO), lysozyme, acid phosphatase (ACP) activities, and superoxide anion generation (O₂^-) rate both at intracellular (P < 0.05) and extracellular (P < 0.05) levels. Besides, alkaline phosphatase (AKP) in hemocytes exhibited no significant differences across the groups (P > 0.05). β-glucan significantly influenced (P < 0.05) the activities of the antioxidant enzyme, superoxide dismutase (SOD) in hemocytes. Moreover, the relative mRNA expression of numerous immune-related genes, including proPO, TLR-2, Alf-1, NOX, Lysozyme, Crustin-1, and Cuznsod, was significantly higher stimulated hemocytes than in control (P < 0.05). We also reported the dose-dependent antiparasitic activity against Mesanophyrs sp., in stimulated hemocytes than in the control (P < 0.05). The present study collectively demonstrated that β-glucan potentially stimulates innate immunity by elevating cellular enzyme responses and up-regulating the mRNA expression of genes associated with crab innate immunity. Thus, β-glucan is a promising immunostimulant for swimming crab farming in crustaceans aquaculture.

Influences of dietary vitamin D3 on growth, antioxidant capacity, immunity and molting of Chinese mitten crab (Eriocheir sinensis) larvae

This study investigates the effects of vitamin D₃ (VD₃) on growth performance, antioxidant capacity, immunity and molting of larval Chinese mitten crab Eriocheir sinensis. A total of 6,000 larvae (7.52 ± 0.10 mg) were fed with six isonitrogenous and isolipidic experimental diets with different levels of dietary VD₃ (0, 3000, 6000, 9000, 12000 and 36000 IU/kg) respectively for 23 days. The highest survival and molting frequency were found in crabs fed 6000 IU/kg VD₃. Weight gain, specific growth rate, and carapace growth significantly increased in crabs fed 3000 and 6000 IU/kg VD₃ compared to the control. Broken-line analysis of molting frequency, weight gain and specific growth rate against dietary VD₃ levels indicates that the optimal VD₃ requirement for larval crabs is 4825-5918 IU/kg. The highest whole-body VD₃ content occurred in the 12000 IU/kg VD₃ group, and the 25-dihydroxy VD₃ content decreased with the increase of dietary VD₃. The malonaldehyde content was lower than the control. Moreover, the superoxide dismutase activity, glutathione peroxidase and total antioxidant capacity of crab fed 6000 IU/kg VD₃ were significantly higher than in control. Crabs fed 9000 IU/kg showed the highest survival after 120 h of salinity stress, and the relative mRNA expressions indicate vitamin D receptor (VDR) is the important regulatory element in molting and innate immunity. The molting-related gene expressions showed that the response of crab to salinity was self-protective. This study would contribute to a new understanding of the molecular basis underlying molting and innate immunity regulation by vitamin D₃ in E. sinensis.

Mass Spectrometric Profiling of Neuropeptides in Response to Copper Toxicity via Isobaric Tagging

Copper is a necessary nutrient but quickly becomes toxic at elevated levels. To properly handle environmental copper influxes and maintain metal homeostasis, organisms utilize various methods to chelate, excrete, and metabolize heavy metals. These mechanisms are believed to involve complex signaling pathways mediated by neuropeptides. This study incorporates custom N,N-dimethyl leucine isobaric tags to characterize the neuropeptidomic changes after different time points (1, 2, and 4 h) of copper exposure in a model organism, blue crab, Callinectes sapidus. Using a modified simplex optimization strategy, the number of identifiable and quantifiable neuropeptides was increased 3-fold to facilitate a deeper understanding of the signaling pathways involved in responding to heavy metal exposure. The time course exposure showed many interesting findings, including upregulation of inhibitory allatostatin peptides in the pericardial organs. Additionally, there was evidence of transport of a pigment dispersing hormone from the sinus glands to the brain. Overall, this study improves the multiplexing capabilities of neuropeptidomic studies to understand the temporal changes associated with copper toxicity.

Effects of environmental antidepressants on colour change and locomotor behaviour in juvenile shore crabs, Carcinus maenas

Juvenile crabs of Carcinus maenas thrive in coastal waters reputed to be the receptacle of continental pollution. Amongst the many pollutants encountered, antidepressants, such as fluoxetine (FLX) and venlafaxine (VEN), often detected at the ng•L^-1 range, are particularly worrying because of their action on the levels of monoamines, such as serotonin, noradrenaline and dopamine. In crustaceans, those monoamines are involved in colour change through their action on neuropeptide hormones. In addition, they are known to have a role in different behaviours, such as locomotion. Both colour change and locomotion are strategies used by juvenile crabs to hide and escape from predators. To investigate if the presence of antidepressants may alter behaviours of ecological importance, juvenile crabs were exposed to environmentally realistic concentrations of either 5 ng•L^-1 of FLX alone or in combination with VEN at 5 ng•L^-1. The ability to change colour depending on the environment and the locomotor activity of juvenile crabs were monitored weekly over 25 days. Animals exposed to antidepressants displayed a different pattern of colour change than the controls, especially those exposed to the combination of FLX and VEN at 5 ng•L^-1 each, and were less efficient to adapt to their environment, i.e., they were not as pale and not as dark as controls or crabs exposed to FLX at 5 ng•L^-1. Moreover, juvenile crabs exposed to the combination of antidepressants exhibited an enhanced locomotor activity throughout the exposure period with a higher velocity and distance moved as well as more time spend moving. The alteration of cryptic behaviours, such as colour change and locomotion by antidepressants persistently present in marine environment at low concentrations may have an impact on the survival of juvenile of C. maenas on the long term.

The effects of vesicle toxin from the sea anemone Bunodosoma cangicum on the behavior of a freshwater shrimp, Palaemon argentinus, and shore crab, Neohelice granulata

Sea anemones of the genus Bunodosoma possess along their body column, longitudinally arranged brown-colored vesicles. We have shown that in B. cangicum, these warty structures contain a mixture of potent toxins. This work highlights the neuro-inhibitory effects exhibited by two decapod crustacean species exposed to the extracts from these vesicles. For this, we use the unrefined toxin in doses, exposure times, and different exposure pathways. The findings show that at least one neuro-inhibitory compound is present and remains active regardless of the exposure method or dose tested. This toxin affects neuro-motor pathways but not neuro-sensory pathways. Shrimp exposed to toxin could continue to perceive and track food pellets but could not secure and consume their ration. Of six anatomical reflexes tested under the toxin's influence, voluntary movements of the mouthparts were impacted most commonly. Interestingly, all subject animals recovered from the toxin exposure within 2 h. Finally, we propose Reflexive Action Analysis (RAMP) as a tool to evaluate the potency of other neurotoxic or neuro-inhibitory compounds in crustacea. This work is the first to show the neuro-inhibitory activity of extracts from these sea anemone columnar vesicle structures and the first to evaluate these effects using RAMP reflex analysis.

The Effect of Glyphosate on the Reproduction of Estuarine Crabs: Neohelice granulata as a Study Model

This review summarizes the bulk of evidence about the effect of glyphosate, both technical and formulated, on the ovarian maturation of Neohelice granulata female crabs, as well as the effects of glyphosate on sperm production in males of the same species. After long-term in vivo assays, made during the 3-month pre-reproductive period of this species, both formulated and technical glyphosate were able to produce a significant incidence of oocyte reabsorption in the ovary, together with a concomitant decreased of vitellogenin content, at concentrations ranging from 0.2 to 1 mg/L. Despite this, after 32-day in vivo assays, glyphosate stimulated oocyte growth, in terms of a higher percentage of vitellogenic oocytes, suggesting that glyphosate could be acting as an endocrine disruptor. In vitro assays made with isolated ovarian pieces showed a decrease of vitellogenin content, in correlation with lower protein synthesis, although some advance in maturation was observed in the histological analysis. In male crabs exposed in vivo to both technical and formulated glyphosate at 1 mg/L, several reproductive imbalances were noted, such as a significant decrease of the sperm count, abnormal spermatophores, and possible disrupting effects of glyphosate on the androgenic gland.

The protective effects of melatonin on survival, immune response, digestive enzymes activities and intestinal microbiota diversity in Chinese mitten crab (Eriocheir sinensis) exposed to glyphosate

Glyphosate is one of the most widely used pesticides, which can cause toxicity to aquatic animals. In this study, the survival rate, immune response, digestive enzyme activities, and the intestinal microbiota diversity of Chinese mitten crab (Eriocheir sinensis) were evaluated after 14 days of exposure to glyphosate (48.945 mg/L from 50% 96 h LC50 value) and melatonin feeding (80 mg/kg). The results showed that MT significantly improved the survival rate, antibacterial capacity of E. sinensis (P < 0.05). After exposure to glyphosate, the expression of Hsp60, Hsp70 and Hsp90 in cranial ganglia and thoracic ganglia was decreased significantly, but MT significantly raised the expression of these proteins (P < 0.05). Glyphosate significantly decreased lipase activity compared with the control group (P < 0.05), while melatonin significantly increased the lipase, amylase and trypsin activities (P < 0.05). Melatonin significantly increased the Chao1 and Shannon index and the relative abundance of Proteobacteria and Bacteroidetes (P < 0.05). This study shows that melatonin has a protective effect on the glyphosate exposed E. sinensis.

Effects of dietary T-2 toxin on gut health and gut microbiota composition of the juvenile Chinese mitten crab (Eriocheir sinensis)

The current study aims to investigate the effects of dietary T-2 toxin on the intestinal health and microflora in the juvenile Chinese mitten crab (Eriocheir sinensis) with an initial weight 2.00 ± 0.05 g. Juvenile crabs were fed with experimental diets supplemented with T-2 toxin at 0 (control), 0.6 (T1 group), 2.5 (T2 group) and 5.0 (T3 group) mg/kg diet for 8 weeks. Dietary T-2 toxin increased the malondialdehyde (MDA) content and the expression of Kelch-like ECH-associated protein 1 (keap1) gene while the expression of cap 'n' collar isoform C (CncC) decreased in the intestine. The activities of glutathione peroxidase (GSH-Px) and total anti-oxidation capacity (T-AOC) in the intestine increased only in the lower dose of dietary T-2. Dietary T-2 toxin significantly increased the mRNA expression of caspase-3, caspase-8, Bax and mitogen-activated protein kinase (MAPK) genes and the ratio of Bax to Bcl-2 accompanied with a reduction of Bcl-2 expression. Furthermore, T-2 toxin decreased the mRNA levels of antimicrobial peptides (AMPs), peritrophic membrane (PM1 and PM2) and immune regulated nuclear transcription factors (Toll-like receptor: TLR, myeloid differentiation primary response gene 88: Myd88, relish and lipopolysaccharide-induced TNF-α factor: LITAF). The richness and diversity of the gut microbiota were also affected by dietary T-2 toxin in T3 group. The similar dominant phyla in the intestine of the Chinese mitten crab in the control and T3 groups were found including Bacteroidetes, Firmicutes, Tenericutes and Proteobacteria. Moreover, the inclusion of dietary T-2 toxin of 4.6 mg/kg significantly decreased the richness of Bacteroidetes and increased the richness of Firmicutes, Tenericutes and Proteobacteria in the intestine. At the genus level, Dysgonomonas and Romboutsia were more abundant in T3 group than those in the control. However, the abundances of Candidatus Bacilloplasma, Chryseobacterium and Streptococcus in T3 group were lower than those in the control. This study indicates that T-2 toxin could cause oxidative damage and immunosuppression, increase apoptosis and disturb composition of microbiota in the intestine of Chinese mitten crab.

Effects of graded levels of starch on the non-specific immune responses, antioxidant capacities and intestinal health in Chinese mitten crab, Eriocheir inensis

A 9-week feeding trial was conducted to investigate the effects of graded levels of dietary starch (12%, 17%, 22%, 27% and 32%) on growth, non-specific immune responses, antioxidant capacities, immunity genes expression levels and pathogen resistance in Chinese mitten crab, Eriocheir inensis (initial body weight: 10.5 ± 0.5 g). Results showed that the highest weight gain rate of crabs was obtained in group containing 22% dietary starch. The highest activity of acid phosphatase, phenoloxidase and lysozyme in blood was found in crabs fed with 22-27% dietary starch. Additionally, 17%-27% dietary starch significantly increased the activities of superoxide dismutase and glutathione peroxidase, reduced malondinaldehyde content and then increased the total antioxidant capacities in hepatopancreas of crabs. The highest activity of alanine aminotransferase and aspartate aminotransferase was found in crabs fed with 32% dietary starch, indicating that excess starch had a negative effect on the liver function of crabs. With the dietary starch level increased, the transcription factors gene expression of the pro-inflammatory factors were significantly up-regulated, and the highest ILF2, IL-16, Relish and ADAM10 was found in crabs fed with dietary 32% starch, which may potentially promote the inflammatory response in intestines. Moreover, with the dietary starch increased, the activity of phenoloxidase and lysozyme, as well as the gene expression of crustin, were all increased in crabs after challenge against Citrobacter freundii, which demonstrated that additional dietary starch could provide immune-protection and help crabs improve their resistance against pathogens. In conclusion, these results suggest that adequate dietary starch can increase growth, enhance innate immune responses and promote disease resistance, reduce oxidative stress and inflammatory response in E. inensis. Taken together, 22-27% dietary starch (25.9-30.8% dietary carbohydrate) was suggested as a digestible energy source in crabs feed.

Micro-algal astaxanthin could improve the antioxidant capability, immunity and ammonia resistance of juvenile Chinese mitten crab, Eriocheir sinensis

Green alga Haematococcus pluvialis is an important source of natural astaxanthin (Ast), which have been shown to be beneficial for the color formulation, survival, antioxidation, immunity and stress resistance of many crustacean. This study was conducted to investigate the effects of dietary supplementation of H. pluvialis meal on growth, antioxidant status, ammonia resistance, color parameters, and carotenoids composition of juvenile Chinese mitten crab Eriocheir sinensis. Five diets were formulated to contain 0, 30, 60, 90 and 120 mg/kg dry diets of natural Ast (defined as Diet 1-5) using H. pluvialis meal as astaxanthin source. The results showed that: (1) Although all treatments with Ast supplementation had the relatively higher growth performance and survival than the control (Diet 1 treatment), no significant differences were found on growth performance, feed conversion ratio and hepatosomatic index among all treatments. (2) The highest total antioxidant capacity (T-AOC) in hepatopancreas and hemolymph were observed in Diet 4 and 3 treatments respectively, while the lowest malondialdehyde (MDA) contents in hepatopancreas and hemolymph were also found in these two treatments. Furthermore, the significantly positive relationships were detected on acid phosphatase (ACP) activities and dietary Ast contents for hepatopancreas and hemolymph. (3) Diet 3 treatment had the highest mRNA levels of EsLecA, EsTrx, and EsPrx6 in hepatopancreas, while both Diet 3 and 4 treatments reached the peaks for mRNA expression levels of EsMyd88 and EsHc, respectively. (4) The stress test with ammonia-N indicated Diet 1 treatment had the highest mortality among all treatments, and the lowest mortality was found on Diet 3 treatment during the stress test. (5) Dietary Ast significantly improved the redness (a*) of carapace and hepatopancreas, which were consistent with the Ast contents in these tissues from the different treatments. Ast concentrations in carapace reached the plateau for Diet 3 treatment while hepatopancreatic Ast concentration kept increasing with elevating dietary Ast contents. In conclusion, natural astaxanthin could enhance the antioxidative capability, non-specific immunity, tissue Ast contents and stress resistance to ammonia-N, and these results suggested the optimal diet micro-algal astaxanthin was around 60 mg/kg for juvenile E. sinensis.

Sodium butyrate can improve intestinal integrity and immunity in juvenile Chinese mitten crab (Eriocheir sinensis) fed glycinin

Butyrate is a fermentation byproduct of gut microbiota and is susceptible to chronic oxidative stress. This study investigates the mitigative effects of sodium butyrate (SBT) on growth inhibition and intestinal damage induced by glycinin in juvenile Chinese mitten crab (Eriocheir sinensis). All four experimental diets containing 80 g/kg glycinin were formulated with 0, 10, 20 and 40 g/kg SBT respectively. There was no glycinin or SBT in the control diet. Juvenile crabs (0.33 ± 0.01g) were respectively fed with these five diets for eight weeks. The diets with 10 and 20 g/kg SBT significantly improved the survival and weight gain of the crabs compared with those in the 0 g/kg SBT group, and showed no difference with the control group. The crabs fed diets containing glycinin without SBT had lower glutathione and glutathione peroxidase activities but higher malondialdehyde in the intestine than those in the control group. Moreover, dietary glycinin decreased the lysozyme and phenoloxidase activities and improved the level of histamine in the intestine compared with the control group, while the supplementation of SBT counteracted these negative effects. The addition of SBT could also restore the impaired immunity and morphological structure of the intestine. Dietary SBT could increase the mRNA expression of antimicrobial peptides genes (anti-lipopolysaccharide factor 1 and 2) and decrease the content of pro-inflammatory factor TNF-α. The SBT could restore the intestinal microbial community disorganized by glycinin. The abundance of pathogenic bacteria (Aeromonas, Vibrio and Pseudomonas) decreased significantly and the potential probiotic bacteria (Bacillus, Lactobacillus, Chitinibacter and Dysgonomonas) increased significantly in the 10 g/kg SBT group. This study suggests that sodium butyrate supplementation can mitigate the negative effects induced by glycinin such as growth inhibition, intestinal inflammation and reduction of beneficial flora in the gut.

Tissue Accumulation and the Effects of Long-Term Dietary Copper Contamination on Osmoregulation in the Mudflat Fiddler Crab Minuca rapax (Crustacea, Ocypodidae)

We examined copper accumulation in the hemolymph, gills and hepatopancreas, and hemolymph osmolality, Na⁺ and Cl^- concentrations, together with gill Na⁺/K⁺-ATPase and carbonic anhydrase activities, after dietary copper delivery (0, 100 or 500 Cu µg g^-1) for 12 days in a fiddler crab, Minuca rapax. In contaminated crabs, copper concentration decreased in the hemolymph and hepatopancreas, but increased in the gills. Hemolymph osmolality and gill Na⁺/K⁺-ATPase activity increased while hemolymph [Na⁺] and [Cl^-] and gill carbonic anhydrase activity decreased. Excretion likely accounts for the decreased hemolymph and hepatopancreas copper titers. Dietary copper clearly affected osmoregulatory ability and hemolymph Na⁺ and Cl^- regulation in M. rapax. Gill copper accumulation decreased carbonic anhydrase activity, suggesting that dietary copper affects acid-base balance. Elevated gill Na⁺/K⁺-ATPase activity appears to compensate for the ion-regulatory disturbance. These effects of dietary copper illustrate likely impacts on semi-terrestrial species that feed on metal-contaminated sediments.

Comparative acute toxicity of glyphosate-based herbicide (GBH) to Daphnia magna, Tisbe longicornis, and Emerita analoga

The aim of this work was to know the differential composition of the dissolved fraction of a glyphosate-based herbicide (GBH), commercialized as GLIFOPAC, when reaches different aquatic environments and its ecotoxicological effects on crustaceans species living in them. Daphnia magna, Tisbe longicornis, and Emerita analoga were exposed to glyphosate herbicide called GLIFOPAC (480 g L-1 of active ingredient or a.i.) at concentrations between 0.5 and 4.8 g a.i. L-1. Acute toxicity in D. magna (48 h-LC50), E. analoga (48 h-LC50), and T. longicornis (96 h-LC50) was studied. Chromatographic analysis of the GBH composition used and water (freshwater/sea water) polluted with GLIFOPAC were evaluated. Results reported acute toxicity (48-96 h-LC50) values for D. magna, E. analoga and T. longicornis of 27.4 mg L-1, 806.4 mg L-1, and 19.4 mg L-1, respectively. Chromatographic evaluation described around 45 substances of the GLIFOPAC composition, such as from the surfactant structures (aliphatic chain with esther/ether group), metabolites (AMPA), and other substances (glucofuranose, glucopyranoside, galactopyranose). This study evidenced differences in the GLIFOPAC composition in freshwater and marine water, which may differentiate the toxic response at the crustacean-level in each aquatic environment.

Metal-Associated Biomarker Responses in Crabs from a Marine Protected Area in Southeastern Brazil

The environmental quality of a Ramsar wetland site located at the Cananéia-Iguape-Peruíbe Protected Area (CIP-PA), in São Paulo, Brazil, was assessed by geochemical analyses and biomarker assessments (GPx, GST, GSH, GST, MT, LPO, DNA damage) performed in swimming crab Callinectes danae Smith, 1869 organs (posterior and anterior gills and hepatopancreas) to estimate sediment contaminant bioavailability. The results indicated that two sampling stations, PT and PM, exhibited the worst environmental conditions, as sediments collected at both points contained metal contamination, while crabs exhibited significant responses for GPx, GST, and LPO (mostly during winter). Sediment contamination tended to be associated to fine sediments (both seasons) and organic matter (winter). During the summer survey, Pb concentrations in sediments of station PT exceeded the Brazilian Sediment Quality Guidelines (SQGs) and the Canadian Interim Marine Sediment Quality Guidelines. Metal concentrations in sediments sampled in winter were higher compared with summer, with Co, Ni, and Pb exceeding SQGs levels at PT, whereas Co, Ni, Hg, Zn, and Pb exceeded SQGs at PM. Biomarker induction during summer appeared to be caused by natural variables (water salinity and temperature, and molting cycle), whereas oxidative stress and tissue damage during winter appeared to be more clearly linked to metal contamination. Anterior gills presented the clearest signs of seasonal variability, being more responsive to sediment contamination. The results suggest that metals originated from the upper Ribeira de Iguape River are transported toward the estuarine system, causing effects on C. danae individuals. Additionally, seasonality is a strong factor concerning CIP-PA toxicity, since the rainfall regime significantly modifies the freshwater flow and, consequently, estuarine water salinity, suspended particle and metal inputs, as well as the location of depositional areas. Thus, efforts to mitigate CIP-PA contamination should be based on the control of upstream pollution sources.

Clone, identification and functional characterization of a novel toll (Shtoll1) from the freshwater crab Sinopotamon henanense in response to cadmium exposure and Aeromonas hydrophila infection

Toll is essential in innate immune system which is important for defense against bacterial, fungal and viral infections in invertebrates. Our previous study showed that cadmium (Cd) could change the expression pattern of ShToll3 in the epithelium (gills and midgut from the freshwater crab Sinopotamon henanense) infected by Aeromonas hydrophila. To investigate the diverse innate immune roles of crustacean homolog Tolls, in this study, we cloned Shtoll1 from S. henanense. The full-length cDNA of Shtoll1 was 4746 bp, with an ORF of 3033 bp encoding a putative protein of 111 amino acids, a 5'-untranslated region of 255 bp and a 3'-untranslated region of 1713 bp. Phylogenetic analysis showed that ShToll1 was clustered into the group of DmToll1, DmToll 4 and DmToll 5. In addition, the tissue distribution results showed that Shtoll1 was expressed widely in different tissues, with the highest expression in heamocytes. Besides, Shtoll1 expressions were upregulated in heamocytes and hepatopancreas after A. hydrophila infection. At the same time, the increase of Shtoll1 expressions were examined in heamocytes in response to Cd exposure and A. hydrophila infection in combination. Through western blotting and immunohistochemical analysis, the ShToll1 expressions in heamocytes were increased in response to A. hydrophila and Cd independently as well as in combination. Moreover, the mRNA level of three antimicrobial peptides (AMPs) alf5, alf6, and c-lys, which possibly responded to Cd and A. hydrophila stimulation through Shtoll1, were analyzed. Thus, we conclude that Cd expand the susceptibility of ShToll1 to A. hydrophila infection in heamocytes. This suggest that ShToll1 may contribute to the innate immune defense of S. henanense against A. hydrophila and Cd in heamocytes.

Dietary glutathione supplementation enhances antioxidant activity and protects against lipopolysaccharide-induced acute hepatopancreatic injury and cell apoptosis in Chinese mitten crab, Eriocheir sinensis

Eriocheir sinensis (E. sinensis) is an important aquaculture species in China. However, deteriorating water environments lead to oxidative stress in these crabs, which subsequently reduces their quality and yield. Glutathione (GSH) is an endogenous antioxidant that is used to mitigate oxidative stress. However, whether dietary GSH can enhance the resistance of E. sinensis to oxidative stress remains unclear. Herein, crabs were fed dietary GSH (the basal diet was supplemented with 0, 300, 600, 900, and 1200 mg/kg diet weight of GSH) for up to 3 weeks and, then, challenged with lipopolysaccharide (LPS; 400 μg/kg body weight). After 6 h, their hepatopancreas were sampled. Diet supplementation with 600 and 900 mg/kg diet weight GSH not only increased the content of GSH in the hepatopancreas, but also enhanced the activities and mRNA expressions of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and glutathione-S-transferase (GST) (P < 0.05), compared to that in control crabs challenged with LPS alone. Diet supplementation with 600 or 900 mg/kg GSH also significantly increased the enzyme activities of GSH reductase and γ-glutamyl cysteine synthetase (γ-GCS) in LPS-treated crabs. Haematoxylin-eosin (HE) staining, electron microscopy, and flow cytometry were used to examine the structure and subcellular structure of and apoptosis in the hepatopancreas. The histopathology and sub-microstructure analysis results also showed that diet supplementation with 600 or 900 mg/kg GSH significantly alleviated damage in crabs challenged with LPS and decreased reactive oxygen species (ROS) levels and cell apoptosis ratios in the hepatopancreas, compared to the LPS-treated crabs. To further understand the effect of dietary GSH on LPS-induced apoptosis, the activities and gene or protein expressions of apoptosis-related factors were evaluated. As a result, diet supplementation with 600 or 900 mg/kg GSH significantly decreased the activities of caspases-3, -8, and -9 and inhibited the relative expression of caspase-3 and -8 but increased the expression of B-cell lymphoma-2 (bcl-2) and B-cell lymphoma-2-associated X inhibitor (bax inhibitor) in crabs challenged with LPS. This treatment further significantly downregulated the relative protein levels of caspase-3, -8, -9 and Bax and upregulated those of Bcl-2 in crabs challenged with LPS. However, treatment with 1200 mg/kg GSH caused the opposite effects. Overall, our results reveal that appropriate diets supplemented with 600 or 900 mg/kg GSH could enhance the antioxidant capacity and anti-apoptotic mechanisms in crabs after LPS injection, thereby providing a theoretical basis for the application of dietary GSH in E. sinensis.

Oxidative stress, immunological response, and heat shock proteins induction in the Chinese Mitten Crab, Eriocheir sinensis following avermectin exposure

In this study, the Chinese mitten crabs, Eriocheir sinensis were exposed to avermectin at 0.03, 0.06, 0.12, 0.24, and 0.48 mg/L respectively for 96 hours. The results showed that levels of superoxide dismutase, catalase, and glutathione peroxidase in hepatopancreas were slightly induced at concentration of 0.03 and 0.06 mg/L, but significantly (P < .05) decreased at higher concentrations, meanwhile similar trend of the activities of acid phosphatase, alkaline phosphatase and lysozyme were observed. Significant induction of HSP70 and HSP90 mRNA expression was detected at 24 hours whereas no significant change was found in HSP60. In addition, levels of reactive oxygen species in hepatocytes increased in dose- and time- dependent manners, and cell viabilities of hepatocytes and haemocytes decreased. These results indicated that sublethal concentration exposure of avermectin had a prominent oxidative stress effect on E. sinensis based on the antioxidative and immunological activity inhibition, and HSP60, 70, and 90 perform a protective response during the exposure.

Immune response to abamectin-induced oxidative stress in Chinese mitten crab, Eriocheir sinensis

It is known that abamectin (ABM) inflicts oxidative damage on aquatic animals; however, knowledge about the immune response under pesticide-induced oxidative stress is incomplete. In the present study, several cellular and humoral immune parameters, including total haemocyte counts (THC), lysosomal membrane stability (LMS), activities of acid phosphatase (ACP), alkaline phosphatase (AKP) and lysozyme (LZM) were investigated to reveal the effects of ABM exposure on the immune defence mechanisms of the important freshwater crab, Erocheir sinensis. According to the results, a significant increase of THC was found in low concentration groups (0.03 and 0.06 mg/L), while dramatic decreases occurred in high concentration groups (0.12 and 0.24 mg/L) after 96 h of exposure. We also detected significant increases of reactive oxygen species (ROS) in haemocytes at 0.12 and 0.24 mg/L, and there was a dose- and time-dependent decrease of lysosomal membrane stability. These results suggest that the excessive generation of ROS induced by ABM may be leading the massive collapse of lysosomal membrane, which in turn may be causing the sharp drop of haemocyte counts in E. sinensis. The increase of hydrolytic enzymes ACP and AKP at low concentrations and the decrease at high concentrations also indicate an immune response associated with haemocytes status under stress. However, activities of LZM decreased significantly. After injection of Aeromonas hydrophil, mortalities increased under exposure to ABM and were positively related to ABM concentration. These results confirm that ABM exposure has the ability to impair immune defence and result in the host's susceptibility to pathogens.

Wastewater bioremediation by mangrove ecosystems impacts crab ecophysiology: In-situ caging experiment

Mangroves are tidal wetlands that are often under strong anthropogenic pressures, despite the numerous ecosystem services they provide. Pollution from urban runoffs is one such threats, yet some mangroves are used as a bioremediation tool for wastewater (WW) treatment. This practice can impact mangrove crabs, which are key engineer species of the ecosystem. Using an experimental area with controlled WW releases, this study aimed to determine from an ecological and ecotoxicological perspective, the effects of WW on the red mangrove crab Neosarmatium africanum. Burrow density and salinity levels (used as a proxy of WW dispersion) were recorded, and a 3-week caging experiment was performed. Hemolymph osmolality, gill Na⁺/K⁺-ATPase (NKA) activity and gill redox balance were assessed in anterior and posterior gills of N. africanum. Burrow density decreased according to salinity decreases around the discharged area. Crabs from the impacted area had a lower osmoregulatory capacity despite gill NKA activity remaining undisturbed. The decrease of the superoxide dismutase activity indicates changes in redox metabolism. However, both catalase activity and oxidative damage remained unchanged in both areas but were higher in posterior gills. These results indicate that WW release may induce osmoregulatory and redox imbalances, potentially explaining the decrease in crab density. Based on these results we conclude that WW release should be carefully monitored as crabs are key players involved in the bioremediation process.

Interference of an atrazine commercial formulation with the endocrine control of ovarian growth exerted by the eyestalks

Atrazine is currently one of the most used herbicides worldwide. We tested the possible effect of the widely used herbicide atrazine on the endocrine control of ovarian growth exerted by the neurohormones secreted at the eyestalk of the estuarine crab Neohelice granulata. For this, both in vivo and in vitro assays were carried out. The in vivo assay comprised the exposure for 1 month to 3 mg/L of a commercial formulation containing 90% of atrazine as active ingredient (Gesaprim 90 WDG®, Syngenta) on three categories of females: intact, ablated of one eyestalk, and ablated of both eyestalks. At the end of the assay, only the intact females showed a significant (p < 0.05) decrease in both content of vitellogenic ovarian proteins and proportion of vitellogenic oocytes, compared to a concurrent control. The results of the in vitro incubation of ovarian pieces with the eventual addition to the incubation medium of eyestalk tissue and/or atrazine at 3 mg/L showed a significant (p < 0.05) decrease in the proportion of vitellogenic oocytes only when atrazine and eyestalk tissue were added. Taken together, these results strongly suggest that the assayed atrazine formulation may act as an endocrine disruptor at the eyestalk level, by altering the normal secretion of some eyestalk hormone, therefore inhibiting ovarian growth.

Effect of nitrite exposure on oxidative stress, DNA damage and apoptosis in mud crab (Scylla paramamosain)

Nitrite is one of major environmental pollutants that can impact immunological parameters in aquatic organisms. In the present study, we investigated the effects of nitrite exposure on oxidative stress, DNA damage and apoptosis in mud crab (Scylla paramamosain). Mud crab were exposed to 0, 5, 10 and 15 mg L^-1 nitrite for 72 h. These data showed that acid phosphatase (ACP) and alkaline phosphatase (ALP) activity significantly decreased in treatments with various concentrations of nitrite (5, 10 and 15 mg L^-1) after 24 and 48 h, while the levels of nitric oxide (NO) significantly increased in these treatments. Nitrite exposure could suppress superoxide dismutase (SOD) and catalase (CAT) activity, and increase the formation of malondialdehyde (MDA) after 48 and 72 h of exposure. In addition, nitrite exposure decreased total haemocyte counts after 48 and 72 h of exposure. Cytological damage, DNA damage and apoptosis was observed obviously at 72 h after nitrite exposure. Moreover, nitrite exposure significantly induced the mRNA levels of phosphorylated Jun N-terminal kinases (JNK), and eventually activated p53 signaling and caspase-3. These results indicated that nitrite exposure could induce oxidative stress, which further caused DNA damage and apoptosis in mud crab. Our results will be helpful to understand the mechanism of nitrite toxicity on crustaceans.

Hidden in the sand: Alteration of burying behaviour in shore crabs and cuttlefish by antidepressant exposure

Pharmaceuticals such as antidepressants are constantly released into the aquatic environment. Consequently, fluoxetine (FLX) and venlafaxine (VEN), the active molecules of Prozac© and Effexor©, are detected up to several µg.L^-1 in freshwater and marine coastal waters. Both compounds act on the serotoninergic system, which may result in behavioural impairment, especially in juvenile animals presumed to be more susceptible to low concentrations than adults. The objective of this study was to determine whether environmental concentrations of FLX alone or combined with VEN modulate innate burying behaviour in two juvenile marine invertebrates, i.e. Sepia officinalis and Carcinus maenas. Juvenile cuttlefish were exposed from hatching to 30 days post-hatching to either FLX alone (i.e. 5 ng.L^-1) or in mixture with VEN (i.e. either 2.5 ng.L^-1 or 5 ng.L^-1 of each antidepressant). Juvenile crabs (<2 cm carapace width) were exposed for a period of 22 days to 5 ng.L^-1 of FLX and a mixture of 5 ng.L^-1 of FLX and VEN each. Several parameters of sand-digging behaviour were analysed weekly in both species. The occurrence of sand-digging behaviour decreased in cuttlefish exposed to a mixture of FLX and VEN at the lowest concentration (2.5 ng.L^-1 each). Because sand-digging behaviour improved in controls, this decrease was likely to be related to a modification of maturation and/or learning processes. At the mixture of 5 ng.L^-1 VEN and FLX each, a better body covering was observed in juvenile crabs. In both species, innate behaviour was modified under exposure to mixtures of FLX and VEN at environmentally realistic concentrations. These alterations were observed at an early developmental stage, when animals are particularly prone to predation. Hence, modified maturation of behavioural traits and, putatively, learning processes by exposure to pseudo-persistent antidepressants may affect the survival of these two species in the long term.

Imbalances in the male reproductive function of the estuarine crab Neohelice granulata, caused by glyphosate

The effect of glyphosate, both pure and formulated (Roundup Ultramax®), was evaluated on males of the estuarine crab Neohelice granulata, by means of both in vivo and in vitro assays. The in vivo assays comprised the exposure for 30 d to 1 mg/L of the herbicide, until finally assessing weight gain, levels of energy reserves, sperm number per spermatophore, proportion of abnormal spermatophores, and sperm viability. At the end of this assay, significant (p < 0.05) decrease in weight gain and muscle protein levels was detected by effect of both pure and formulated glyphosate. In spermatophores from the vas deferens, a significant (p < 0.05) decrease of the sperm count was observed by effect of Roundup, while a significant incidence (p < 0.05) of abnormal spermatophores was observed either with glyphosate or with Roundup treatment. No changes were seen in the spermatophore area or in vas deferens secretions. Since no sperm mortality was induced by the formulated herbicide, we propose a probable inhibiting effect on spermatogenesis might explain the observed sperm count decrease. In this sense, an in vitro assay was designed by incubating testes and vasa deferentia with Roundup, in order to corroborate the possible interference of glyphosate with the secretion of the androgenic gland hormone that controls the spermatogenesis, in the presence or absence of the androgenic gland. Although the herbicide per se was able to reduce the sperm count to some extent, the increase in the number of spermatozoa/spermatophore produced by the co-incubation with the androgenic gland was completely reverted by the addition of Roundup (1 mg/L of glyphosate a.e.), suggesting that an inhibition on the secretion and/or transduction of the androgenic gland hormone could be taking place.

SIFamide peptides modulate cardiac activity differently in two species of Cancer crab

The SIFamides are a broadly conserved arthropod peptide family characterized by the C-terminal motif -SIFamide. In decapod crustaceans, two isoforms of SIFamide are known, GYRKPPFNGSIFamide (Gly¹-SIFamide), which is nearly ubiquitously conserved in the order, and VYRKPPFNGSIFamide (Val¹-SIFamide), known only from members of the astacidean genus Homarus. While much work has focused on the identification of SIFamide isoforms in decapods, there are few direct demonstrations of physiological function for members of the peptide family in this taxon. Here, we assessed the effects of Gly¹- and Val¹-SIFamide on the cardiac neuromuscular system of two closely related species of Cancer crab, Cancer borealis and Cancer irroratus. In each species, both peptides were cardioactive, with identical, dose-dependent effects elicited by both isoforms in a given species. Threshold concentrations for bioactivity are in the range typically associated with hormonal delivery, i.e., 10^-9 to 10^-8 M. Interestingly, and quite surprisingly, while the predicted effects of SIFamide on cardiac output are similar in both C. borealis and C. irroratus, frequency effects predominate in C. borealis, while amplitude effects predominate in C. irroratus. These findings suggest that, while SIFamide is likely to increase cardiac output in both crabs, the mechanism through which this is achieved is different in the two species. Immunohistochemical/mass spectrometric data suggest that SIFamide is delivered to the heart hormonally rather than locally, with the source of hormonal release being midgut epithelial endocrine cells in both Cancer species. If so, midgut-derived SIFamide may function as a regulator of cardiac output during the process of digestion.

Lactic acid bacteria, Enterococcus faecalis Y17 and Pediococcus pentosaceus G11, improved growth performance, and immunity of mud crab (Scylla paramamosain)

Mud crabs (Scylla paramamosain), a commercially important cultured species in the southeastern region of China, is usually infected by Vibriosis or parasites, causing great economic losses in cultured farms. Previous studies have demonstrated that probiotics benefited in enhancing the immune response against invading pathogens in aquatic animals. In this study, the effects of dietary administration of lactic acid bacteria (LAB) (Enterococcus faecalis Y17 and Pediococcus pentosaceus G11) on growth performance and immune responses of mud crab were assessed. Both strains (Y17 and G11) showed an inhibitory activity against bacterial pathogens (Aeromonas hydrophila, Vibrio parahaemolyticus, Vibrio alginolyticus, Staphylococcus aureus, and β Streptococcus), and a wide pH tolerance range of 2-10. In vivo, mud crabs were fed a control diet and experimental diets supplemented with 10⁹ cfu g^-1 diet either Y17 or G11 for 6 weeks before subjecting to a challenge test with V. parahaemolyticus for 12 h. The probiotic-supplemented diets had significant effects on weight gain and specific growth rate during the feeding trial. Increased serum enzyme activities of phenoloxidase, lysozyme, and SOD were observed in the hemolymph of mud crab in Y17 and G11-supplemented groups compared to that in the controls (P < 0.01). The significantly up-regulated expression of gene CAT, LYS, proPO, and SOD could be seen in hepatopancreas in G11-supplemented groups. After the pathogenicity test, the survival rate of Y17 + and G11 + V. parahaemolyticus groups was 66.67% and 80.00%, respectively, compared with 53.33% for the control groups. Taken together, dietary supplementation of Y17 and G11 strains were beneficial in mud crab, which could increase growth performance, modulate immune system and protect the host against V. parahaemolyticus infection.

Arginine supplementation improves growth, antioxidant capacity, immunity and disease resistance of juvenile Chinese mitten crab, Eriocheir sinensis

To investigate the effects of arginine (Arg) on the growth, antioxidant capacity, immunity and disease resistance of juvenile Chinese mitten crab, three diets containing Arg levels at 1.72% (control), 2.73% and 3.72% were formulated and fed to Chinese mitten crab (0.22 ± 0.03 g) for eight weeks. The weight gain, ecdysterone and growth hormone in the serum, relative expression of insulin-like growth factor 2 in the hepatopancreas significantly increased in crabs fed the 2.73% and 3.72% Arg diets. The protein and lipid contents significantly increased in crabs fed the 3.72% Arg diet. The feed conversion ratios in crabs fed the diets with Arg additions were lower than in the control. Arg supplementation also enhanced the antioxidative capacity by increasing the activities of superoxide dismutase, catalase and the relative expression of Kelch-like ECH-associated protein 1 gene in the hepatopancreas, which subsequently decreased malondialdehyde content in the hepatopancreas. Besides, Arg also decreased nitric oxide content in the serum and the activity of nitric oxide synthetase in the hepatopancreas. The relative mRNA levels of crustin, relish, lysozyme and cryptocyanin genes were significantly upregulated by Arg supplementation. The activities of acid phosphatase and alkaline phosphatase in the serum significantly increased in crabs fed the 3.72% Arg diet than those in the control. Similarly, the relative mRNA levels of crustin, cryptocyanin and proPO genes were significantly upregulated in crabs fed the 2.73% Arg diet after lipopolysaccharide challenge, and in crabs fed the 3.72% Arg diet after the Poly (I:C) challenge. The crabs fed the 2.73% and 3.72% Arg diets had higher survival rate after bacterial infection than those fed the control diet. This study indicates that the addition of Arg to the diet at 2.7-3.7% can improve the growth, survival, antioxidant capacity, immunity and disease resistance in juvenile Chinese mitten crab.

Ammonia toxicity in the mud crab (Scylla paramamosain): The mechanistic insight from physiology to transcriptome analysis

Ammonia is a major aquatic environmental pollutants. However, the underlying molecular mechanism of ammonia-induced toxicity is not fully understood. In this study, we investigated the physiological response and molecular mechanism in mud crab (Scylla paramamosain) exposed to the acute total ammonia (30 mg L^-1) for 48 h. The results shown that ammonia exposure induced oxidative stress, and subsequently led to cytological damage and DNA damage. Transcriptome analysis was applied to investigate the key genes and pathways involved in the responses to ammonia exposure. A total of 722 differentially expressed genes (DEGs) (526 up-regulated and 196 down-regulated) were identified. DEGs mainly involved in pathways including metabolism, cellular processes, signal transduction and immune functions. Additionally, transcriptome analysis revealed that ATM/p53-Caspase3 pathway involved in apoptosis induced by ammonia stress. These results provided a new insight into the mechanism of the potential toxic effects of ammonia on crustaceans.

Risk assessment of chlorantraniliprole pesticide use in rice-crab coculture systems in the basin of the lower reaches of the Yangtze River in China

Rice-crab (Chinese mitten crab, Eriocheir sinensis) coculture system has become one of the most important agricultural activities practiced in China. However, the effect of pesticide usage on the survival and edible safety of crab species living in the coculture system has not been investigated. In the present study, we created a field simulation experiment and discovered that the amount of pesticide chlorantraniliprole (CAP) entering the rice-crab coculture system accounted for 82.22% of the total CAP content present in the spray barrel. When CAP residues found in the soil leached into nearby areas, we observed an increase in the CAP concentration in the water and sediment. Specifically, peak CAP concentration (1.35 μg/L) was detected in water within 1 day, and a steady CAP concentration in the sediment (2.55 μg/kg) was detected within 3 days. Additionally, an extensive field sampling experiment conducted in the basin of the lower reaches of the Yangtze River revealed that CAP was routinely used in rice-crab coculture systems. Although detected CAP concentrations were below 1 μg/L in ditch water and below 1 μg/kg in ditch sediment, there was still a potential risk associated with the crab growth. Importantly, there was no risk associated with crab consumption, given the low detection frequency of CAP in the collected samples. Our analysis suggests that an increase in usage ratio and a decrease in the total CAP content will likely promote safe application of CAP in the rice-crab coculture systems.

Combined effects of waterborne copper exposure and salinity on enzymes related to osmoregulation and ammonia excretion by blue crab Callinectes sapidus

Copper is essential, but can be toxic to aquatic organisms when present in high concentrations. In freshwater crustaceans, copper inhibits enzymes related to ionic and osmoregulation and to the ammonia efflux, that leads to Na⁺ imbalance and inhibition of ammonia excretion. In the animals inhabiting estuarine or seawater, mechanisms of copper toxicity is not clear, but had been described as disruption of ionregulation and metabolism. To clarify the mechanism of copper toxicity in crustaceans inhabiting variable salinity, this work investigated whether copper affects ammonia excretion and enzymes used for ammonia balance and osmoregulation in the blue crab Callintectes sapidus acclimated to salinity 2 and 30 ppt. To achieve this, juveniles of the blue crab were exposed to 63.5 µg/L of copper at both salinities for 96 h. This is an environmentally realistic copper concentration. Results of ammonia efflux, free amino acids and Na⁺ concentrations in hemolymph, Na⁺/K⁺-ATPase, H⁺-ATPase and, carbonic anhydrase (CA) activities in gills were consistent with the osmoregulatory pattern adopted by the blue crab, which hyperosmoregulates at salinity 2 ppt and osmoconforms at 30 ppt. At 30 ppt copper reduced free amino acid in hemolymph of crabs, suggesting an effect of the metal on osmotic performance. At 2 ppt, copper significantly increased the H⁺-ATPase activity involved in ammonia excretion. This may be a compensatory response of crabs to maintain low levels of ammonia in their hemolymph; which can be increased by copper exposure. Results presented here are useful for the improvement of the Biotic Ligand Model (BLM) to predict copper toxicity for saltwater environments.

Dietary nano cerium oxide promotes growth, relieves ammonia nitrogen stress, and improves immunity in crab (Eriocheir sinensis)

Oxidative stress plays a crucial role in ammonia nitrogen toxicity. In this study, the beneficial effects of dietary nano cerium oxide (nano CeO₂) as a potent antioxidant were examined in the Chinese mitten crab (Eriocheir sinensis). Crabs were fed a diet supplemented with 0, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4, or 12.8 mg/kg nano CeO₂ for 60 d. The optimum supplementation level of nano CeO₂ that significantly increased weight gain rate and decreased feed coefficient was 0.8 mg/kg. This level also offered immune protection when crabs were kept under ammonia nitrogen stress and/or exposed to pathogen infection (Aeromonas hydrophila). Supplementation with 0.8 mg/kg of CeO₂ (i) relieved pathological damage to the hepatopancreas; (ii) increased hemocyte counts, including total number of hemocytes, granulocytes, and hyalinocytes; (iii) decreased malondialdehyde content and increased antioxidant enzyme activities of superoxide dismutase and catalase in the hemolymph; (iv) increased the activities of lysozyme, acid phosphatase, and alkaline phosphatase in the hemolymph; and (v) increased gene and protein expression of cathepsin L in the hepatopancreas. Mortality increased when crabs were injected with bacteria under ammonia nitrogen stress, but dietary supplementation with 0.8 mg/kg nano CeO₂ decreased the mortality rate. Thus, the results of this study suggested that dietary supplementation with nano CeO₂ in crabs promoted growth and up-regulated immunity to bacterial infection under ammonia nitrogen stress.

Effect of estradiol on hepatopancreatic lipid metabolism in the swimming crab, Portunus trituberculatus

Estradiol is an important sex steroid hormone that involved in regulation of animal lipid metabolism. However, the effect of estradiol on lipid metabolism in swimming crab (Portunus trituberculatus) is unclear. The present study investigated the effect of four concentrations of exogenous estradiol (0, 0.01, 0.1 and 1 μg g^-1 crab weight) on the expression levels of lipid metabolism-related genes, lipid composition and histology of hepatopancreas in the P. trituberculatus. The results showed that the mRNA levels of carnitine palmitoyltransferase I and II (CPT-I and CPT-II) increased significantly at the low concentrations (0.01 μg g^-1 and 0.1 μg g^-1), while decreased significantly in the highest concentration (1 μg g^-1). The mRNA levels of acyl-CoA oxidase (ACOX), fatty acid transport protein (FATP), fatty acid-binding protein (FABP), diacylglycerol acyltransferase 1 (DGAT1) and acetyl-CoA carboxylase (ACC) were significantly down-regulated. The transcripts of fatty acid synthase (FAS) and fatty acyl desaturase (FAD) decreased significantly only in 1 μg g^-1 treatment. All estradiol treatments (0.01, 0.1 and 1 μg g^-1) had significantly higher percentages of 20:4n6, 20:5n3 and 22:6n3, but lower percentages of total monounsaturated fatty acids and polar lipids than the control treatment (0 μg g^-1). Histological observations indicated the size of B cell became larger under estradiol treatment. The results indicated that estradiol promoted lipid catabolism in the hepatopancreas of P. trituberculatus.

Effects of lactic acid on drug-metabolizing enzymes in Chinese mitten crab (Eriocheir sisnensis) after oral enrofloxacin

Enrofloxacin (ENR) is the most commonly used antibiotic in crustacean farming in China. Diet supplementation with lactic acid (LA) may, however, affect the efficacy and safety of ENR-based drugs. The aims of this study were to investigate the effects of LA on drug residues and elimination of oral ENR in Chinese mitten crab (Eriocheir sinensis) and to determine ENR and gene expression levels of drug-metabolizing enzymes in the hepatopancreas. To this end, ENR was orally administered to the crabs at a dose of 10.0 mg kg^-1 body weight on the eighth day after feeding diets supplemented with 0.3%LA. The results showed that ENR levels in the hepatopancreas were significantly different at 1 and 12 h between the ENR and ENR + 0.3% LA groups (P < 0.05). Lactic acid did not significantly affect the expression of CYP2A (phase I). However, the expressions of CYP3 (phase I) and GST (phase II) were significantly up-regulated by LA during the elimination process of ENR (6-24 h). At T_max (1 h), the expression of phosphoenolpyruvate carboxykinase (PEPCK) was induced and expression of succinate dehydrogenase (SDH) was inhibited by LA. Both of these enzymes were significantly inhibited during the elimination process of ENR. The results suggest that LA contributes to the elimination of ENR, and thus, enhances hepatopancreas biotransformation and anti-injury capacity in E. sinensis.

Effects of the glyphosate-based herbicide roundup on the survival, immune response, digestive activities and gut microbiota of the Chinese mitten crab, Eriocheir sinensis

Glyphosate is one of the most widely used pesticides in the world and can be transported easily by surface runoff, air, and rivers, potentially affecting aquaculture. In this study, the survival rate, intestinal and hepatopancreatic immune and digestive functions, and the intestinal microbial diversity of Chinese mitten crab (Eriocheir sinensis) were evaluated after 7 days of exposure to glyphosate (48.945 mg/L from 1/2 96-h LC50 value). The results showed that glyphosate significantly reduced the survival rate of E. sinensis. After exposure to glyphosate, the totoal antioxidant capacity (T-AOC) in the midgut and hindgut of E. sinensis was significantly decreased, and malondialdehyde (MDA) content in the midgut was significantly increased (P < 0.05). After glyphosate exposure, the activities of digestive enzymes (including lipase and amylase) in the intestinal tract were significantly decreased and trypsin was significantly increased, while three enzymes in the hepatopancreas were significantly increased (P < 0.05). Using high-throughput sequencing analysis of the gut microbiota, the results showed that glyphosate significantly decreased the diversity of E. sinensis gut microbiota, while significantly increasing the taxonomic richness of Bacteroidetes and Proteobacteria (P < 0.05). This study suggested that these bacteria may be involved in glyphosate effects on survival by regulation of immune and digestive function.

Combined effects of temperature and copper on oxygen consumption and antioxidant responses in the mudflat fiddler crab Minuca rapax (Brachyura, Ocypodidae)

This study investigates the combined effects of waterborne copper exposure and acute temperature change on oxygen consumption and the oxidative stress biomarkers, glutathione S-transferase (GST) and glutathione peroxidase (GPx), in the gills and hepatopancreas of the fiddler crab Minuca rapax. Crabs held at 25 °C were acclimated to 0 (control), 50, 250 or 500 μg Cu L^-1 for 21 days, and were then subjected to 15, 25 and 35 °C for 24 h. Aerial oxygen consumption rates of crabs in copper free media increased with increasing temperature from 15 to 35 °C, Q₁₀ values reaching ≈3. Crabs exposed to increasing copper concentrations exhibited variable responses, Q₁₀ values falling to ≈1.5. Copper had no effect on oxygen consumption at 25 °C. However, at 35 °C, rates decreased in a clear concentration-response manner in the copper exposed crabs, revealing impaired aerobic capability. At 15 °C, oxygen consumption rates increased with copper concentration, except for a decrease at 500 μg Cu L^-1. Gill GST activity was ≈2-fold that of the hepatopancreas, while hepatopancreas GPx activity was 3-fold that of the gills. Gill GST activities were reduced by copper exposure only at 25 °C while hepatopancreas GST activities were altered by copper at all temperatures. Hepatopancreas GST and GPx activities increased in crabs exposed to copper at 35 °C, revealing oxidative stress induction. Hepatopancreas GST and GPx activities were reduced in copper exposed crabs at 15 °C, suggesting a diminished capability to mitigate the effects of copper exposure at low temperature. These findings reveal that copper exposure increases oxygen consumption at low temperatures but decreases consumption at high temperature. Hepatopancreas GPx activities decreased at low temperature and increased at high temperature. These novel findings demonstrate that the interaction between copper exposure and temperature should be considered when evaluating biomarker activities in semi-terrestrial crabs.

Effects of copper on larvae of the marbled crab Pachygrapsus marmoratus (Decapoda, Grapsidae): Toxicity test and biochemical marker responses

The importance of trace elements in ecotoxicological investigations is a well-known issue when monitoring polluted areas such as commercial harbors. Copper represents one of the most common metal contaminants, often detected in these areas as it is widely employed in various fields and has many sources of inflow in the marine environment. Pachygrapsus marmoratus is a widespread intertidal crab species that has been extensively studied in ecology, ethology and population genetics. Ecotoxicological studies have also been performed, exclusively on the adult stage. In the present study we investigated the mortality and biochemical (oxidative stress and neurotoxicity) responses of P. marmoratus larvae exposure to environmental relevant concentration of copper. Results showed dose-dependent responses in terms of larval mortality, with a calculated LC₅₀ value of 0.5 mg/L of Cu²⁺. The LC₅₀ concentration was used as the starting point for subsequent biochemical response evaluation. Results also demonstrated dose-dependent activation of antioxidant systems assuming a compensatory antioxidant activity to prevent higher cellular damage when larvae were exposed to the highest concentrations of copper. Moreover, a significant enhancement of neurotransmitter activities was observed, assuming a possible direct interaction of copper with the enzymes or an increase of free copper ion aliquot into the cells.

Can the Atlantic ghost crab be a potential biomonitor of microplastic pollution of sandy beaches sediment?

The objective of the present study was to test whether the Atlantic ghost crab Ocypode quadrata is a reliable biomonitor of microplastic (MP) pollution of beach sediments. To test the hypothesis (H1) that the sediment is the main source of MP ingestion, the proportion of MP types (hard plastic, microfibers, pellet, soft plastic, and extruded polystyrene foam) in the gut content was compared with that on the strandline. The types of MPs in the gut content and sediment had similar proportions; black (~49%) and blue (~45%) microfibers were responsible for this similarity (55%), hence confirming H1. However, the second hypothesis (H2) that prevalence of MP in the gut content is related to its density on beach with distinct urbanization degree was not accepted. These results indicate that high trophic plasticity of the ghost crab and, consequently, multiple-sources of contamination may interfere with its use as a biomonitor of MP pollution.

Tamoxifen affects the histology and hepatopancreatic lipid metabolism of swimming crab Portunus trituberculatus

Tamoxifen (TAM) is an antiestrogenic agent and can enter the aquatic environment in wastewater. It has been reported that TAM can induce hepatic steatosis in vertebrates, however, the effects of TAM exposure on lipid metabolism of hepatopancreas in crustaceans remains unclear. In this study, four TAM concentrations (0, 6.7, 13.4 and 20 μg g^-1 crab body weight) were injected into the swimming-leg of swimming crabs Portunus trituberculatus, as a means of evaluating the effects of TAM on the expression levels of lipid metabolism-related genes, lipid composition, and hepatopancreas histology. The results showed that the mRNA levels of three lipogenic related genes (diacylglycerol acyltransferase 1 (DGAT1), acetyl-CoA carboxylase (ACC) and fatty acyl desaturase (FAD)) decreased significantly in the 6.7 μg g^-1 and 20 μg g^-1 TAM treatments compare to the control. The mRNA levels of fatty acid synthase (FAS) decreased significantly in a dose-dependent manner as TAM concentration increased. The mRNA levels of two lipid catabolism-related genes (acyl-CoA oxidase (ACOX) and fatty acid transport protein (FATP)) were down-regulated among the three TAM treatments, while the enzyme activity and mRNA level of carnitine palmitoyltransferase I (CPT-I) was up-regulated by TAM treatments. Compared to the control, the lowest levels of total lipids and phospholipids were detected in the 6.7 μg g^-1 TAM treatment, while the 20 μg g^-1 TAM treatment had the lowest free fatty acids concentration. The 6.7 μg g^-1 TAM treatment had the lowest percentages of 16:1n-7, 18:1n-9, 18:1n-7 and total monounsaturated fatty acids (∑MUFA), whilst simultaneously recording the highest percentages of 18:2n-6 and 20:2n-6 in this treatment. Moreover, histological observations indicated that TAM caused the walls of the hepatopancreatic tubules to become brittle, with a concurrent increase in the number of blister-like cells. These results suggest that TAM damages the hepatopancreas and leads to a reduction in hepatopancreatic lipid deposition in P. trituberculatus.

Enzymatic and Histological Biomarkers in Ucides cordatus (Crustacea, Decapoda) in an Industrial Port on the North Coast of Brazil

The aim of this study was to evaluate enzymatic (glutathione-S-transferase and catalase) and histological (branchial lesions) biomarkers in Ucides cordatus (Crustacea, Decapoda) from an industrial port region on the north coast of Brazil. The crabs were collected in two distinct locations of the Brazilian coast: A1 = region under influence of port activities; and A2 = low-impacted area. We performed histological examination in the gills and glutathione-S-transferase (GST) and catalase activity in the hepatopancreas. The most frequent and severe histological lesions were found in A1, especially rupture of pilaster cells and lamellar collapse. Catalase activity did not show a pattern capable of differentiating the two analyzed areas. On the other hand, GST activity presented a more pronounced response in the crabs of the port area (p < 0.05), coinciding with the most frequent branchial lesions in these same organisms. These results suggest that the species is susceptible to environmental stress, once alterations at different organizational levels were verified.

Impacts of circadian rhythm and melatonin on the specific activities of immune and antioxidant enzymes of the Chinese mitten crab (Eriocheir sinensis)

Many physiological functions of crustaceans show a rhythmic change to adapt to daily environmental cycles. However, daily variation in the immune and antioxidant status and its possible correlation with circulatory melatonin levels during the daily cycle have not been reported in the Chinese mitten crab, Eriocheir sinensis. In this study, the specific activities of immune and antioxidant enzymes of E. sinensis during the 24 h cycle and its relationship with injected doses of melatonin were evaluated. The results showed that the immune parameters in the hemolymph, such as total hemolymph count, alkaline phosphatase, lysozyme, acid phosphatase, and phenol oxidase, exhibited bimodal patterns during the 24 h cycle, these parameters were synchronized with the activity of antioxidant enzymes such as malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase, and catalase. However, there was only one peak in the muscle (during 1200-1600 h) and gills (during 0400-0800 h). The survival rate reached approximately 80% in 5 days when melatonin concentrations were lower than 0.05 g/L, significantly decreasing as melatonin concentrations increased. Four hours after melatonin injection, MDA levels in the muscle and hemolymph were significantly lower than those in the control group. Eight hours after melatonin injection, SOD levels in the hemolymph were significantly higher than those in the control group. These findings highlight the importance of considering circadian regulation of innate immunity when comparing immune responses at fixed times.

Biochemical and morphological responses in Ucides cordatus (Crustacea, Decapoda) as indicators of contamination status in mangroves and port areas from northern Brazil

The aims of this study were to analyze biochemical and morphological responses (glutathione S-transferase activity and branchial lesions) in Ucides cordatus (crabs) and to verify how the species is responding to environmental contamination in a port (potentially contaminated area) and mangrove (reference area; Amazon Coast, Maranhão, Brazil). Adult males were captured bimonthly for a period of 1 year. Higher GST activity (1.03 ± 0.07 μmol min^-1 mg protein^-1) was observed in crabs in the port when compared with those in the reference area (p < 0.05). The greatest number of branchial lesions (serious alterations) was recorded in crabs only in the port area. The GST activity increased until serious lesions appeared; after this limit, GST activity decreased dramatically to very low levels, thus resulting in irreversible lesions (lamella collapse). The mathematical model based on the two parameters evaluated in U. cordatus showed that the port area experienced substantial contamination impact, while the mangroves (reference area) presented moderate environmental quality.

Assessment of the heavy metal accumulation in the Blue Swimmer Crab (Portunus pelagicus), northern Bay of Bengal: Role of salinity

This is the first report to assay the heavy metal accumulation in Blue Swimmer Crab in the northern Bay of Bengal. The present study finds that copper (Cu) concentration though has been the highest compared to the other metals, particularly in the gill. Cadmium (Cd) and lead (Pb) have high affinity to be concentrated in Hepatopancreas all through the year. All the metal concentrations were higher during monsoon season (comparatively low salinity) than non-monsoon (high salinity) in the different body parts of Blue swimmer crab i.e. the inverse relationship between accumulation of heavy metals and sea water salinity has been shown. Present study revealed that salinity having the role to accumulate metal in different body parts of Blue Swimmer Crab. In future, microcosm experiments should be done to test the effect of frequent fluctuations of ambient salinity, such as is usual in different seasons in the present study area.

Leucoxenols A and B, two new phenolics from Bornean medicinal plant Syzygium leucoxylon

The medicinal plant, Syzygium leucoxylon or commonly known as Obah found in North Borneo was considered as traditional medicine by local committee. Two new phenolics, leucoxenols A (1) and B (2) were isolated and identified as major secondary metabolites from the leaves of S. leucoxylon. Their chemical structures were elucidated based on spectroscopic data such as NMR and HRESIMS. Furthermore, these compounds were active against selected strains of fungi.

Immune response, MT and HSP70 gene expression, and bioaccumulation induced by lead exposure of the marine crab, Charybdis japonica

In order to understand the mechanisms of the toxicity of lead (Pb) on invertebrates, the immunotoxic effects of Pb in the marine crab, Charybdis japonica, were evaluated in the present study. The crabs were exposed to 0.066, 0.132, 1.318, 2.636, 6.590, and 13.181 μM of lead acetate and a control over 30 days, and the hemolymph was sampled terminally for testing the immunity-related indices, including total hemocyte count (THC), hemocyanin content, the activities of the phenoloxidase (PO) and lysozyme (LSZ). In addition, tissue samples were collected from the hepatopancreas, gill, muscle and ovary after 30 days of exposure for detecting the Pb accumulation in the major organs. The gene expression profiles of metallothionein (MT) and heat shock protein 70 (HSP70) in the hepatopancreas of C. japonica upon exposure to lead acetate over 96 h were also analyzed. The results showed a decline in the majority of the immunity-related parameters after an initial rise, and their levels were significantly lower in the treatment groups compared with those in the control, except in the group exposed to 0.066 μM of lead acetate for 30 days. Furthermore, a significant negative correlation was observed between the lead acetate concentration and the hemocyanin content, the activities of PO and LSZ (P<0.01). The expression levels of MT and HSP70 genes were rapidly induced, reaching a peak level after 12 and 24 h of exposure, respectively, and remained at a significantly higher level than the control after 96 h of exposure. It was also observed that the distribution pattern of Pb in the tissues of exposed crabs was in the order of gill > hepatopancreas > ovary and muscle, and exhibited a concentration-dependent response. Taken together, the results revealed that Pb exposure induced the immunosuppression of C. japonica and resulted in bioaccumulation, which could subsequently increase the disease susceptibility and threaten the food safety.

Evaluation of the acute toxicity of mahua oil cake aqueous extract and its effect on the behavioral responses of the freshwater grapsid crab, Varuna litterata (Fabricius, 1798)

Mortality and behavioral alterations are monitored as the sensitive endpoints in toxicological studies and may be applied as useful biomarkers to assess piscicidal pollution in aquatic environment. Present study assesses acute toxicity of the piscicide, mahua oil cake (MOC), and its effect on the behavioral responses of the freshwater grapsid crab, Varuna litterata, under laboratory conditions. To determine the LC50 values, a 4-day acute static renewal toxicity test was done where 10 adult male crabs (mean length 2.870 ± 0.379 cm; mean weight 9.891 ± 3.951 g) were exposed to different concentrations (1, 5, 10, 15, 20, 25, 30, 35 ppt) of MOC aqueous extract with a control at different exposure periods. The LC50 values are 19.109 ppt for 24 h, 16.052 ppt for 48 h, 11.827 ppt for 72 h, and 7.631 ppt for 96 h. The high LC50 values indicate less sensitivity of this crab to the MOC extract than other aquatic animals. MOC extract has toxic effect on the mouthparts activity, whirling motion of water current producing activity, froth releasing activity, aggregation, balance and coordination actions, medium escaping behavior, locomotor activity, and fecal matter excretion of this crab in different exposure periods. Behavioral responses such as froth releasing activity, aggregation, and medium escaping behavior can be used as biomarkers of MOC pollution in aquatic environment.

Antioxidative status, immunological responses, and heat shock protein expression in hepatopancreas of Chinese mitten crab, Eriocheir sinensis under the exposure of glyphosate

As a broad-spectrum herbicide, glyphosate was extensively utilised in China for several decades. The contradiction between glyphosate spraying and crab breeding in the rice-crab co-culture system has become more obvious. In this study, the antioxidative status and immunological responses of Chinese mitten crab, Eriocheir sinensis, under sublethal exposure of glyphosate were investigated by detecting the antioxidative and immune-related enzyme activity, acetylcholinesterase (AChE) activity and relative mRNA expression of heat shock proteins (HSPs) in hepatopancreas. The results showed that high concentrations of glyphosate (44 and 98 mg/L) could induce significant alteration of superoxide dismutase (SOD), peroxidase (POD), acid phosphatase (ACP), alkaline phosphatase (AKP), and phenoloxidase (PO) activities by first rising then falling during the exposure. However, AChE activity in all treatments including 4.4 mg/L was inhibited markedly after 6 h of exposure. In addition, the relative mRNA expression of HSP 60, HSP 70, and HSP 90 was significantly upregulated at both 48 h and 96 h. These results revealed that glyphosate has a prominent toxic effect on E. sinensis based on antioxidative and immunological response inhibition and AChE activity reduction even at the lowest concentration of 4.4 mg/L, and a protective response by upregulation of HSPs was carried out by the species to ease the environmental stress.

Carbamazepine disrupts molting hormone signaling and inhibits molting and growth of Eriocheir sinensis at environmentally relevant concentrations

Carbamazepine (CBZ), one of the most frequently detected pharmaceutical compounds in aquatic environments, has recently been shown to cause chronic toxicity and endocrine disruption in a variety of non-target aquatic organisms. However, neither the effects nor the specific mechanism of CBZ action on the molting of crustaceans is well understood. The aim of this study was to investigate the effects of CBZ on the molting and growth of the Chinese mitten crab Eriocheir sinensis, a native and economically important species in China, and to elucidate the specific mechanisms through which molt inhibition occurs. Juvenile E. sinensis were treated with four nominal environmentally relevant concentrations (0.01, 0.1, 1, or 10 μg/L) of CBZ for acute (4 days) and chronic (40 days) exposures. After acute exposure, chitinase activity in the epidermis and 20-hydroxyecdysone (20-HE) concentration in the hemolymph were significantly decreased (p < 0.05) following treatment with 10 μg/L CBZ, whereas epidermal chitobiase activity significantly decreased (p < 0.05) in response to both 1 and 10 μg/L CBZ treatments. Transcript levels of the genes encoding crustacean hyperglycemic hormone (chh) and molt-inhibiting hormone (mih) in the eyestalks were also markedly induced after 1 or 10 μg/L CBZ treatment (p <  0.05), whereas the expression of genes encoding ecdysone receptor (ecr) and crustacean retinoid X receptor (rxr) in the hepatopancreas were significantly suppressed (p < 0.05) after acute exposure. Moreover, under chronic exposure, CBZ inhibited the molting and growth of E. sinensis, resulting in a longer time before molting was completed (TBM), as well as a lower molting increment (MI) with 1 or 10 μg/L treatment (p < 0.05). Collectively, these data indicate that CBZ can inhibit the molting process of E. sinensis by interfering with the activity of chitinolytic enzymes and molting hormone signaling, suggestive that carbamazepine may have long-term effects on crab development. We also confirmed that CBZ may function as an endocrine disruptor in decapod crustaceans, a phenomenon that has previously been reported in vertebrates.

The protective effects of melatonin on oxidative damage and the immune system of the Chinese mitten crab (Eriocheir sinensis) exposed to deltamethrin

Deltamethrin (Del), an important broad-spectrum insecticide, is widely used in agricultural activities. However, Del is an effective reactive oxygen species (ROS) inducer that induces oxidative stress damage in cells or tissues. Del is significantly more toxic to aquatic organisms, especially crustaceans, than to mammals and birds. This study was designed to evaluate the protective effect of melatonin (MT) on the toxicity-induced damage of Del after 6 h in Eriocheir sinensis. The results showed that Del exposure significantly induced oxidative damage in the hepatopancreas and mitochondria, with malondialdehyde (MDA) and glutathione (GSH) levels being significantly increased and superoxide dismutase (SOD) activity being significantly decreased. Moreover, Del exposure significantly induced functional damage of the hepatopancreas and mitochondria, with a significant increase in alanine aminotransferase (ALT), aspartate aminotransferase (AST), acid phosphatase (ACP) and alkaline phosphatase (AKP) activities in the hepatopancreas and the ratio of albumin/globulin (ALB/GLB) in serum, which indicated the permeability and integrity of the membranes were damaged and had caused cell damage. In addition, ATP content, Na⁺-K⁺-ATPase activity and cytochrome C (Cyt‑C) content in mitochondria decreased significantly, which indicated that Del exposure destroyed the normal respiratory chain of mitochondria. We also evaluated the hematological parameters. Although there were no significant differences in total hemocyte count (THC) levels, hemocyte apoptosis was significantly induced by Del exposure, and the hemocyte phagocytic activity and the hemocyanin levels decreased significantly with Del exposure. However, MT pretreatment not only prevented oxidative damage and functional damage caused by Del exposure to the hepatopancreas and mitochondria, but it also restored the hemocyte apoptotic rate and phagocytic activity to normal levels. In short, Del exposure caused significant oxidative and functional damage to the hepatopancreas, mitochondria and hemocytes of E. sinensis, whereas the use of MT almost completely eliminated the damage caused by Del exposure.