A review of gastric processing in decapod crustaceans

Zinc stable isotopes in mangrove crabs as tracers of anthropogenic contamination in a tropical estuary

Our study presents a novel approach for tracing anthropogenic zinc (Zn) bioaccumulation in mangrove crabs using Zn stable isotope compositions (δ66Zn). We analyzed δ66Zn and elemental composition in crab tissues from Brazilian mangroves within a coastal lagoon historically impacted by electroplating waste. Crabs from the mangrove area near the old electroplating plant exhibited the highest Zn concentrations in both muscle and hepatopancreas, likely reflecting the high Zn bioavailability in these sediments. In contrast, crabs from other mangrove sites showed minimal variations in Zn concentrations, despite prominent differences in sediment Zn levels. This suggests that crabs regulate their internal Zn concentrations within a specific range, not correlating with external Zn bioavailability. The tissues of crabs from contaminated sites bore heavier δ66Zn, consistent with the δ66Zn left by industrial Zn pollution in sediments. However, δ66Zn did not correlate directly with either bioaccumulated Zn or sediment Zn levels, making it challenging to distinguish between stations with varying contamination degrees. Shifting δ66Zn in crab tissues toward lighter isotopes compared to sedimentary Zn indicates the influence of diet, internal biological fractionation, specific bioaccumulation pathways, or additional Zn sources. Biological fractionation within crabs likely caused muscle tissues to be isotopically lighter than the hepatopancreas, especially in moderately contaminated areas. This first systematic study of δ66Zn within mangrove crabs highlights the need for further research to fully understand isotopic variations in crab tissues and their relationship with environmental, ecological, and physiological factors. Initial findings suggest that sources, bioaccumulation routes, and regulatory mechanisms shape δ66Zn within crab tissues.

In vitro controlled release of the probiotic strain Bacillus licheniformis PPL2016 microencapsulated: Simulating the digestive system by age class and sex in the blue swimming crab Callinectes arcuatus

This work aims to encapsulate Bacillus licheniformis PPL2016 (12 × 106 CFU/mL), a marine probiotic characterized at a biochemical and molecular level, in sodium alginate (2%) microparticles and to evaluate its controlled and directed release in a simulated digestive system (DS) of the swimming crab Callinectes arcuatus, considering the following age classes and sexes: Adult Female, Juvenile Female, Adult Male, and Juvenile. The encapsulation process was carried out using the ionic gelation technique. The microcapsules were characterized physiochemically by their size, morphology, number of encapsulated bacteria after the encapsulation process, as well as bacterial survival after 45 days of storage (4 °C). The in vitro release and survival studies of bacteria inside the organs that make up the DS of C. arcuatus were carried out using a protocol developed in our laboratory by applying extracts of dissected organs from the DS (stomach, hepatopancreas and intestine) of the swimming crab. A χ2 test (α = 0.05) was performed at linearization (Log10) of the percentages of the controlled releases of microencapsulated B. licheniformis PPL2016 at different times (0 h, 4 h, 8 h, 12 h), corresponding to the extracts of the organs which simulated the digestive system of C. arcuatus. After biochemical characterization B. licheniformis PPL2016 was considered probiotic bacteria. Microparticles with an average size of 602 to 639 µm were obtained after using the ionic gelation method. Bacterial survival and encapsulation efficacy showed high cell viability and performance above 77.94%. Stability studies showed that storage at a temperature of 4 °C, kept almost 100% of viable bacteria for 15 days; however, cell viability decreased to a survival of 90% after 30 days of storage at this temperature. Regardless of reduced cell viability after 30 days, there are enough viable bacterial cells. Release and survival studies showed that alginate particles had a protective effect on bacteria, these results suggest that microparticles can be produced by a low-cost method. In juvenile males, the percentage of release of probiotic bacteria was greater in TIV in the enzyme extract of the intestine (12 h) with 95 ± 0.45%. Juvenile males had the lowest in vitro release at the stomach stage (0 h) and thus marks the significance for their low release of microcapsules at the beginning of the in vitro release (χ2 = 6.7509; χ2Calculated Pool = 13.5188; χ2Calculated Critical (0.05, 21) = 11.5919; p < 0.05), with the highest significance in the intestine (12 h) (χ2 = 1.2602; χ2Calculated Pool = 13.5188; χ2Calculated Critical (0.05, 21) = 11.5919; p < 0.05). Significant differences in vitro bacterial release were recorded for age classes and sexes of C. arcuatus.

Why not be larger in wave action sites? Energetic constraints due to body size in hermit crabs

Coping with wave action is energetically demanding. Therefore, the endurance of animals exposed to waves should depend on a long-term balance between energy intake and the energy needed to withstand waves. Since the hydrodynamic forces of lift and drag increase with body size, we expected to find smaller individuals in wave-exposed areas. We sampled the body size distribution of hermit crabs along a gradient of wave action intensity. Then, we experimentally estimated energy budget (assimilated energy, maintenance metabolic rate, and the cost of coping with waves) as a function of body size in individuals exposed to bidirectional water flow at two different intensities for 21 days. We used the exponents of the assimilated energy and of the energetic cost of coping with waves to compute the theoretically predicted optimum and maximum energetic size according to the Sebens model. We found that the cost of coping with waves increased with wave intensity and body size due to the higher energetic demands of physiological maintenance and of remaining attached to the substrate. Although assimilated energy increased with body size under both wave regimes, this increase was less pronounced in the individuals exposed to the stronger wave regime compared to those in the weaker wave treatment. Furthermore, under the stronger experimental wave regime energetic constraints increased with body size, and individuals collected in the field were smaller than the maximum size predicted by the model for a similar wave regime. Together, these results suggest that hermit crabs may exhibit an adaptive submaximal growth strategy to mitigate the hydrodynamic costs of wave action.

Morphological and histochemical characteristics of the foregut, midgut, and hindgut, and their alterations during ovarian development in female freshwater prawn, Macrobrachium rosenbergii

The anatomical, histological, and histochemical characteristics of the foregut (FG), midgut (MG), and hindgut (HG), as well as their alterations during the ovarian cycle in female prawns, Macrobrachium rosenbergii, were investigated. The esophagus (ESO), cardia (CD), and pylorus (PY) are the main components of the FG. An epithelium (Ep) with thick cuticle (Cu) layers lining the ESO, and the ESO is encircled by the ESO glands. The CD has a thick musculature, whereas the Ep of the PY are characterized by numerous villi and columnar Ep cells with a thinner layer of Cu. The inner longitudinal (LM) and the outer circular (CM) muscles were both present in the PY. The MG is lined by Ep cells which are connected to the basement membrane, and it lacks Cu. Microvilli, and subapical vacuoles are visible on the apical surface of Ep cells of the MG. The outermost layer is characterized by a dense strip of elastic fibers and a cluster of collagen fibers. The HG has the Ep cells with a thin Cu layer, and the HG glands form a rosette-like structure. The HG is surrounded by the CM and the LM fibers. The reactivities of Periodic Acid Schiff and Alcian Blue in these digestive organs altered throughout the ovarian cycle, and this was supported by the increased expression of mucin levels as ovarian maturation progressed. Our results offer novel and significant insights into the anatomical and histochemical structures of these digestive organs, and demonstrate a significant correlation between ovarian development and feeding in the female prawn, M. rosenbergii.

Effects of low temperature exposure and acclimation on the behavioural responses of the green crab (Carcinus maenas) from Newfoundland, Canada

European green crab (Carcinus maenas) are a highly successful invasive species of intertidal crustacean. The northern most limit of their invasive range on the east coast of North America is the island of Newfoundland (NL), Canada, where they can experience water temperatures as low as -1 °C during the winter. Green crabs' ability to tolerate a large temperate range is one of the most important characteristics responsible for their invasive success. We investigated the behavioural responses of the green crab to a temperature reduction regime, and long-term acclimation to winter (2 °C) and summer (12 °C) water temperatures in NL. Locomotor activity declined as temperature decreased with a concomitant increase in time spent buried, showing a marked change in these parameters at approximately 4 °C. There was also a marked reduction in activity after long-term exposure to cold temperatures (2 °C) compared to controls (12 °C). However, locomotor activity did not cease completely, even after long-term exposure to 2 °C, indicating that crabs remained responsive to their environment. Crabs took longer to respond to food items and consumed less food after long-term acclimation to 2 °C, compared to 12 °C; however feeding did not cease completely. Collectively, these responses suggest that the green crab enters a dormant state below 5 °C, rather than true torpor, in which they continue to move and feed, albeit more slowly and at lower rates. The green crab population in NL is a genetically hybridized population with both southern and cold-resistant northern haplotypes, however, they react in a similar way to most other populations across their native and invasive range and so the observed behavior may be an inherent reaction to cold.

Effect of partial and total replacement of fishmeal by soybean meal in feed on growth and gut performance of Penaeus vannamei

This study evaluated the growth and gut performance of shrimp fed three isonitrogenous diets (37% crude protein) with varying inclusions of fish meal (FM) and soybean meal (SBM): F1 (27.5% FM), F2 (10% FM + 23.5% SBM), and F3 (38% SBM). Over a 28-day period, feed intake, feed conversion ratio (FCR), and survival rates showed no significant differences among the groups. However, shrimp fed F2 and F3 exhibited significantly higher weight gain and average daily growth (ADG) compared to those fed F1 (P < 0.05). Gut performance analysis revealed that F3 consistently had the highest gut passage time (GPT), while F1 had the lowest. By day 28, shrimp fed F2 displayed elevated gut retention time (GRT). F1-fed shrimp showed a high gut passage rate (GPR), whereas F3-fed shrimp had a low GPR until day 21, with differences becoming negligible by day 28. Histological examination of the hepatopancreas revealed an increased R-cell population in shrimp fed F3. These findings highlight the adaptability of shrimp to different dietary compositions and underscore the importance of considering multiple factors when assessing the impacts of feed on growth and physiology.

Impacts of nanopolystyrene and/or phoxim exposure at environmentally relevant concentrations on the intestinal histopathology, intestinal microbiota, and metabolome in Eriocheir sinensis

Nanopolystyrene (NP) pollution in aquatic environments has become an increasing concern. Phoxim (PHO), one of the major organophosphorus pesticides, has also been detected in aquatic environments, posing serious health risks to crustaceans. This study aimed to assess the detrimental effects of NP and/or PHO exposure at environmentally relevant concentrations on the intestinal histopathology, intestinal microbiota, and metabolome of adult crabs (Eriocheir sinensis) for 21 days. Our study revealed significant histopathological abnormalities in the intestines. In all the exposure groups, there was a discovery of vacuolar degeneration occurring in epithelial cells. Additionally, the peritrophic membrane exhibited thinning after NP or PHO single exposure, while thickening was observed after co-exposure. Exposure to NP and/or PHO disrupted the intestinal microbiota homeostasis, as evidenced by the proliferation of pathogenic bacteria and suppression of beneficial bacteria. Notably, PHO exposure resulted in increased abundance of pathogenic bacteria (Spiroplasma and Arcobacter) and decreased abundance of beneficial bacteria (Bacteroides). Analysis of the metabolome revealed that exposure to NP and/or PHO led to alterations in the metabolic profile as well as several critical pathways. Among these, the upregulation of arachidonic acid metabolism, ABC transporters, and biosynthesis of amino acids was observed in both NP single exposure and co-exposure, while PHO single exposure downregulated these pathways. Additionally, NP and/or PHO exposure downregulated neuroactive ligand-receptor interaction. Spearman correlation analysis revealed that the significant reduction of some differentially expressed metabolites (DEMs) was potentially regulated by the low-abundance bacterial genera following exposure to NP and/or PHO. And these DEMs have a role in anti-inflammatory or antioxidant properties. Collectively, our results offer novel perspectives on the intestinal toxicity of crustaceans by NP and/or PHO at environmentally relevant concentrations.

Distinct Strategies Regulate Correlated Ion Channel mRNAs and Ionic Currents in Continually versus Episodically Active Neurons

Relationships among membrane currents allow central pattern generator (CPG) neurons to reliably drive motor programs. We hypothesize that continually active CPG neurons utilize activity-dependent feedback to correlate expression of ion channel genes to balance essential membrane currents. However, episodically activated neurons experience absences of activity-dependent feedback and, thus, presumably employ other strategies to coregulate the balance of ionic currents necessary to generate appropriate output after periods of quiescence. To investigate this, we compared continually active pyloric dilator (PD) neurons with episodically active lateral gastric (LG) CPG neurons of the stomatogastric ganglion (STG) in male Cancer borealis crabs. After experimentally activating LG for 8 h, we measured three potassium currents and abundances of their corresponding channel mRNAs. We found that ionic current relationships were correlated in LG's silent state, but ion channel mRNA relationships were correlated in the active state. In continuously active PD neurons, ion channel mRNAs and ionic currents are simultaneously correlated. Therefore, two distinct relationships exist between channel mRNA abundance and the ionic current encoded in these cells: in PD, a direct correlation exists between Shal channel mRNA levels and the A-type potassium current it carries. Conversely, such channel mRNA-current relationships are not detected and appear to be temporally uncoupled in LG neurons. Our results suggest that ongoing feedback maintains membrane current and channel mRNA relationships in continually active PD neurons, while in LG neurons, episodic activity serves to establish channel mRNA relationships necessary to produce the ionic current profile necessary for the next bout of activity.

Physiological Responses of the Green Shore Crab, Carcinus maenas, During Acute and Chronic Low Temperature Exposure

The green shore crab (Carcinus maenas) is native to Western Europe but has spread around the globe and is described as one of the top 100 worst invasive species. On the east coast of North America, their northern-most limit is the island of Newfoundland, Canada, where they can experience water temperatures as low as -1 °C. We investigated the physiological responses of C. maenas to a temperature reduction regime as well as to long-term acclimation to temperatures representative of winter (2 °C) and summer (12 °C) in Newfoundland. Heart rate, oxygen consumption and estimated energy expenditure declined steadily with decreasing temperature, but a marked change was observed between 6 and 4 °C, with lowest levels recorded in 2 °C. After long-term acclimation to 2 °C there was a sustained reduction in physiological parameters. Even though these physiological parameters were very low in 2 °C, the crabs still exhibited intermittent activity. This supports the presence of a dormancy, rather than true torpor/hibernation below 5 °C, in which crabs will continue to actively move and feed, albeit much more slowly. The population in Newfoundland contains haplotypes from both the invasive northern and southern lineages, and they appear to retain a similar low temperature response compared with most other populations of green crab from both their native and expanded range.

Ih block reveals separation of timescales in pyloric rhythm response to temperature changes in Cancer borealis

Motor systems operate over a range of frequencies and relative timing (phase). We studied the role of the hyperpolarization-activated inward current (Ih) in regulating these features in the pyloric rhythm of the stomatogastric ganglion (STG) of the crab, Cancer borealis, as temperature was altered from 11°C to 21°C. Under control conditions, rhythm frequency increased monotonically with temperature, while the phases of the pyloric dilator (PD), lateral pyloric (LP), and pyloric (PY) neurons remained constant. Blocking Ih with cesium (Cs+) phase advanced PD offset, LP onset, and LP offset at 11°C, and the latter two further advanced as temperature increased. In Cs+ the frequency increase with temperature diminished and the Q10 of the frequency dropped from ~1.75 to ~1.35. Unexpectedly in Cs+, the frequency dynamics became non-monotonic during temperature transitions; frequency initially dropped as temperature increased, then rose once temperature stabilized, creating a characteristic 'jag'. Interestingly, these jags persisted during temperature transitions in Cs+ when the pacemaker was isolated by picrotoxin, although the temperature-induced change in frequency recovered to control levels. Overall, these data suggest that Ih plays an important role in maintaining smooth transitory responses and persistent frequency increases by different mechanisms in the pyloric circuitry during temperature fluctuations.

Neuromodulator-induced temperature robustness in a motor pattern: a comparative study between two decapod crustaceans

While temperature fluctuations pose significant challenges to the nervous system, many vital neuronal systems in poikilothermic animals function over a broad temperature range. Using the gastric mill pattern generator in the Jonah crab, we previously demonstrated that temperature-induced increases in leak conductance disrupt neuronal function and that neuropeptide modulation provides thermal protection. Here, we show that neuropeptide modulation also increases temperature robustness in Dungeness and green crabs. As in Jonah crabs, higher temperatures increased leak conductance in both species' pattern-generating lateral gastric neuron and terminated rhythmic gastric mill activity. Likewise, increasing descending modulatory projection neuron activity or neuropeptide transmitter application rescued rhythms at elevated temperatures. However, decreasing input resistance using dynamic clamp only restored the rhythm in half of the experiments. Thus, neuropeptide modulation increased temperature robustness in both species, demonstrating that neuropeptide-mediated temperature compensation is not limited to one species, although the underlying cellular compensation mechanisms may be distinct.

The impact of settleable atmospheric particulate on the energy metabolism, biochemical processes, and behavior of a sentinel mangrove crab

We use the sentinel mangrove crab, Minuca rapax, as a model to investigate the effects of metallic settleable particulate matter (SePM) on wetland. Multiple levels of energetic responses, including (i) metabolic rate and energy budget, (ii) oxidative stress, and (iii) behavioral response by righting time, were assessed as well as the metal and metalloid content in crabs exposed to 0, 0.1 and 1 g.L-1 of SePM, under emerged and submerged conditions over five days, simulating the rigors of the intertidal habitat. Al, Fe, Mn, Cr, and Y exhibited a concentration-dependent increase. Metal concentrations were higher in submerged crabs due to the continuous ingestion of SePM and direct exposure through gills. Exposure concentration up to 1 g.L-1 decreased metabolic rate and enzymatic activities, reduced assimilation efficiency and energy for maintenance, and induces a slower response to righting time, probably by metal effects on nervous system and energy deficits. In conclusion, SePM exposure affects the redox status and physiology of M. rapax depending on he submersion regime and SePM concentration. The disruption to the energy budget and the lethargic behavior in M. rapax exposed to SePM implies potential ecological alterations in the mangrove ecosystem with unknown consequences for the local population.

Ih Block Reveals Separation of Timescales in Pyloric Rhythm Response to Temperature Changes in Cancer borealis

Motor systems operate over a range of frequencies and relative timing (phase). We studied the contribution of the hyperpolarization-activated inward current (Ih) to frequency and phase in the pyloric rhythm of the stomatogastric ganglion (STG) of the crab, Cancer borealis as temperature was altered from 11°C to 21°C. Under control conditions, the frequency of the rhythm increased monotonically with temperature, while the phases of the pyloric dilator (PD), lateral pyloric (LP), and pyloric (PY) neurons remained constant. When we blocked Ih with cesium (Cs+) PD offset, LP onset, and LP offset were all phase advanced in Cs+ at 11°C, and the latter two further advanced as temperature increased. In Cs+ the steady state increase in pyloric frequency with temperature diminished and the Q10 of the pyloric frequency dropped from ~1.75 to ~1.35. Unexpectedly in Cs+, the frequency displayed non-monotonic dynamics during temperature transitions; the frequency initially dropped as temperature increased, then rose once temperature stabilized, creating a characteristic "jag". Interestingly, these jags were still present during temperature transitions in Cs+ when the pacemaker was isolated by picrotoxin, although the temperature-induced change in frequency recovered to control levels. Overall, these data suggest that Ih plays an important role in the ability of this circuit to produce smooth transitory responses and persistent frequency increases by different mechanisms during temperature fluctuations.

Neuropeptide Modulation Enables Biphasic Internetwork Coordination via a Dual-Network Neuron

Linked rhythmic behaviors, such as respiration/locomotion or swallowing/chewing, often require coordination for proper function. Despite its prevalence, the cellular mechanisms controlling coordination of the underlying neural networks remain undetermined in most systems. We use the stomatogastric nervous system of the crab Cancer borealis to investigate mechanisms of internetwork coordination, due to its small, well-characterized feeding-related networks (gastric mill [chewing, ∼0.1 Hz]; pyloric [filtering food, ∼1 Hz]). Here, we investigate coordination between these networks during the Gly1-SIFamide neuropeptide modulatory state. Gly1-SIFamide activates a unique triphasic gastric mill rhythm in which the typically pyloric-only LPG neuron generates dual pyloric-plus gastric mill-timed oscillations. Additionally, the pyloric rhythm exhibits shorter cycles during gastric mill rhythm-timed LPG bursts, and longer cycles during IC, or IC plus LG gastric mill neuron bursts. Photoinactivation revealed that LPG is necessary to shorten pyloric cycle period, likely through its rectified electrical coupling to pyloric pacemaker neurons. Hyperpolarizing current injections demonstrated that although LG bursting enables IC bursts, only gastric mill rhythm bursts in IC are necessary to prolong the pyloric cycle period. Surprisingly, LPG photoinactivation also eliminated prolonged pyloric cycles, without changing IC firing frequency or gastric mill burst duration, suggesting that pyloric cycles are prolonged via IC synaptic inhibition of LPG, which indirectly slows the pyloric pacemakers via electrical coupling. Thus, the same dual-network neuron directly conveys excitation from its endogenous bursting and indirectly funnels synaptic inhibition to enable one network to alternately decrease and increase the cycle period of a related network.

Exposure to nanopolystyrene and phoxim at ambient concentrations causes oxidative stress and inflammation in the intestines of the Chinese mitten crab (Eriocheir sinensis)

Nanopolystyrene (NP) and phoxim (PHO) are common environmental pollutants in aquatic systems. We evaluated the toxic effects of exposure to ambient concentrations of NP and/or PHO in the intestines of the Chinese mitten crab (Eriocheir sinensis). Our study showed that histopathological changes were observed in the intestines. Specifically, NP and/or PHO exposure increased intraepithelial lymphocytes. Furthermore, NP and/or PHO exposure induced oxidative stress, as evidenced by a significant decrease in superoxide dismutase activity (SOD), peroxidase activity (POD), and total antioxidant capacity (T-AOC). Pro-inflammatory gene expression and transcriptome analysis demonstrated that NP and/or PHO exposure induced the intestinal inflammatory response. Transcriptome results showed that NP and/or PHO exposure upregulated the NF-κB signaling pathway, which is considered a key pathway in the inflammatory response. Additionally, the expression of pro-inflammatory genes significantly increased after a single exposure to NP or PHO, but it exhibited a significant decrease after the co-exposure. The downregulation of these genes in the co-exposure group likely suggested that the co-exposure mitigated intestinal inflammation response in E. sinensis. Collectively, our findings mainly showed that NP and/or PHO exposure at ambient concentrations induces oxidative stress and inflammatory response in the intestines of E. sinensis.

Prevalence of microplastics in Peruvian mangrove sediments and edible mangrove species

Mangrove ecosystems have been hypothesised as a potential sink of microplastic debris, which could pose a threat to mangrove biota and ecological function. In this field-study we establish the prevalence of microplastics in sediments and commercially-exploited Anadara tuberculosa (black ark) and Ucides occidentalis (mangrove crab) from five different zones in the mangrove ecosystem of Tumbes, Peru. Microplastic were evident in all samples, with an average of 726 ± 396 microplastics/kg for the sediment, although no differences between the different zones of the mangrove ecosystem were observed. Microplastic concentrations were 1.6± 1.1 items/g for the black ark and 1.9 ± 0.9 microplastics/g for the mangrove crab, with a difference in the microplastic abundance between species (p < 0.05), and between the gills and stomachs of the crab (p < 0.01). Human intake of microplastics from these species, for the population in Tumbes, is estimated at 431 items per capita per year. The outcomes of this work highlight that the mangrove ecosystem is widely contaminated with microplastics, presenting a concern for the marine food web and food security.

Oscillatory network spontaneously recovers both activity and robustness after prolonged removal of neuromodulators

Robustness of neuronal activity is a property necessary for a neuronal network to withstand perturbations, which may otherwise disrupt or destroy the system. The robustness of complex systems has been shown to depend on a number of features of the system, including morphology and heterogeneity of the activity of the component neurons, size of the networks, synaptic connectivity, and neuromodulation. The activity of small networks, such as the pyloric network of the crustacean stomatogastric nervous system, appears to be robust despite some of the factors not being consistent with the expected properties of complex systems, e.g., small size and homogeneity of the synaptic connections. The activity of the pyloric network has been shown to be stable and robust in a neuromodulatory state-dependent manner. When neuromodulatory inputs are severed, activity is initially disrupted, losing both stability and robustness. Over the long term, however, stable activity homeostatically recovers without the restoration of neuromodulatory input. The question we address in this study is whether robustness can also be restored as the network reorganizes itself to compensate for the loss of neuromodulatory input and recovers the lost activity. Here, we use temperature changes as a perturbation to probe the robustness of the network's activity. We develop a simple metric of robustness, i.e., the variances of the network phase relationships, and show that robustness is indeed restored simultaneously along with its stable network activity, indicating that, whatever the reorganization of the network entails, it is deep enough also to restore this important property.

Thermal acclimation and habitat-dependent differences in temperature robustness of a crustacean motor circuit

Introduction

At the cellular level, acute temperature changes alter ionic conductances, ion channel kinetics, and the activity of entire neuronal circuits. This can result in severe consequences for neural function, animal behavior and survival. In poikilothermic animals, and particularly in aquatic species whose core temperature equals the surrounding water temperature, neurons experience rather rapid and wide-ranging temperature fluctuations. Recent work on pattern generating neural circuits in the crustacean stomatogastric nervous system have demonstrated that neuronal circuits can exhibit an intrinsic robustness to temperature fluctuations. However, considering the increased warming of the oceans and recurring heatwaves due to climate change, the question arises whether this intrinsic robustness can acclimate to changing environmental conditions, and whether it differs between species and ocean habitats.

Methods

We address these questions using the pyloric pattern generating circuits in the stomatogastric nervous system of two crab species, Hemigrapsus sanguineus and Carcinus maenas that have seen a worldwide expansion in recent decades.

Results and discussion

Consistent with their history as invasive species, we find that pyloric activity showed a broad temperature robustness (>30°C). Moreover, the temperature-robust range was dependent on habitat temperature in both species. Warm-acclimating animals shifted the critical temperature at which circuit activity breaks down to higher temperatures. This came at the cost of robustness against cold stimuli in H. sanguineus, but not in C. maenas. Comparing the temperature responses of C. maenas from a cold latitude (the North Sea) to those from a warm latitude (Spain) demonstrated that similar shifts in robustness occurred in natural environments. Our results thus demonstrate that neuronal temperature robustness correlates with, and responds to, environmental temperature conditions, potentially preparing animals for changing ecological conditions and shifting habitats.

Uniquely preserved gut contents illuminate trilobite palaeophysiology

Trilobites are among the most iconic of fossils and formed a prominent component of marine ecosystems during most of their 270-million-year-long history from the early Cambrian period to the end Permian period1. More than 20,000 species have been described to date, with presumed lifestyles ranging from infaunal burrowing to a planktonic life in the water column2. Inferred trophic roles range from detritivores to predators, but all are based on indirect evidence such as body and gut morphology, modes of preservation and attributed feeding traces; no trilobite specimen with internal gut contents has been described3,4. Here we present the complete and fully itemized gut contents of an Ordovician trilobite, Bohemolichas incola, preserved three-dimensionally in a siliceous nodule and visualized by synchrotron microtomography. The tightly packed, almost continuous gut fill comprises partly fragmented calcareous shells indicating high feeding intensity. The lack of dissolution of the shells implies a neutral or alkaline environment along the entire length of the intestine supporting digestive enzymes comparable to those in modern crustaceans or chelicerates. Scavengers burrowing into the trilobite carcase targeted soft tissues below the glabella but avoided the gut, suggesting noxious conditions and possibly ongoing enzymatic activity.

Widespread learned predator recognition to an alien predator across populations in an amphibian species

Alien predators are a major cause of decline and extinction of species worldwide, since native organisms are rarely equipped with specific antipredatory strategies to cope with them. However, phenotypic plasticity and learned predator recognition may help prey populations to survive novel predators. Here we examine geographical variation in the learning ability of larval spadefoot toads (Pelobates cultripes) to recognize invasive predatory crayfish (Procambarus clarkii). We compare the learning-mediated behavioural responses of tadpoles from six populations across two regions in Spain (central and southern), with different histories of exposure to the presence of the invasive species. Two of the populations showed innate recognition of chemical cues from the invasive crayfish, whereas three of them learned to recognize such cues as a threat after conditioning with conspecific alarm cues. Learning abilities did not differ among southern populations, but they did among central populations. We assessed patterns of genetic variation within and among these two regions through microsatellite markers and found low genetic divergence among the southern populations but greater differentiation among the central ones. We hypothesize that similar responses to the invasive crayfish in southern populations may have arisen from a combination of extended historical exposure to this introduced predator (~ 50 y) and higher levels of gene flow, as they inhabit a highly interconnected pond network. In contrast, populations from central Spain show lower connectivity, have been exposed to the invasive crayfish for a shorter period of time, and are more divergent in their plastic responses.

Interactive effects of food deprivation state and hypoxia on the respiratory responses of postprandial rock crabs, Cancer irroratus

Under the background of climate change, increasing attention has focused on the effects of ocean deoxygenation on marine organisms. However, few studies address the effects of different food deprivation states on hypoxia tolerance. We therefore investigated the metabolic responses of the Atlantic rock crab, Cancer irroratus (starved 28-35 days, fasted 3-5 days and recently fed). Starved-crab exhibited the lowest critical oxygen saturation (S_crit)_, while fed-crab had the highest S_crit. The fed-crab maintained an elevated postprandial oxygen consumption (MO₂) even below the S_crit of fasted-crab indicating reserved aerobic scopes for critical activities in severe hypoxia. Following feeding, hypoxia (50% and 20% oxygen saturation, S_O2) retarded the specific dynamic action resulting in lower peak MO₂ and longer duration. The starved-crab exhibited a lower peak MO₂, prolonged duration and higher energy expenditure than fasted-crab after feeding. The decline in arterial P_O2 was most pronounced below the S_crit for both fasted- and starved-crab. The higher hemocyanin concentration ([Hc]) of fasted-crab (than starved-crab) suggested they had improved oxygen transport capacity, but hypoxia did not increase [Hc] during the 72-h experiment. Following feeding, the fasted-crab significantly increased L-lactate concentration ([L-lactate]) in 20% S_O2, which was not observed in starved-crab. These results suggest starvation may trigger a cross-tolerance to hypoxia. Because crabs can undergo long periods of food deprivation in their natural environment, future studies should consider how this may affect their ability to deal with environmental perturbations.

Bioaccumulation of 35 metal(loid)s in organs of a freshwater mussel (Hyriopsis cumingii) and environmental implications in Poyang Lake, China

Benthic bioaccumulation of hazardous materials has been a great challenge to the health of lake ecosystems. As representative benthic macroinvertebrates, freshwater mussels and their accumulation characteristics have been regarded as effective indicators for assessing potential risks induced by sedimentary metal(loid)s in lakes. Here we profile organ-specific accumulation of 35 metal(loid)s in a freshwater mussel (Hyriopsis cumingii) and their correlations to metal speciation in sediments of Poyang Lake, the largest lake of China. Significant organ-specific characteristics of metal accumulation were found in gills, though higher thallium (Tl) and selenium (Se) were found in the hepatopancreas, and greater arsenic (As) mostly accumulated in gonads. Pearson correlation analysis revealed that the bioaccumulation of silver (Ag), cobalt (Co), and rare earth elements (ΣREE) in gills and As in gonads were closely associated with those in bioavailable fraction of sediments. Based on the biochemical analysis in the major organs, gills exhibited the highest enzymatic activity compared with hepatopancreas and gonads. Sedimentary metals, particularly for available Ag, Co, and ΣREE, play key roles in causing lipid peroxidation in gills and significantly promote the activities of superoxide dismutase (SOD)/glutathione reductase (GR), while many metals (e.g., cadmium, manganese, Se) inhibit the glutathione (GSH) content in gonads and hepatopancreas. Our study indicates a high physiological sensitivity of mussels to these target metals, which highlights the significance of organ-specific accumulation of metal(loid)s in understanding the potential ecological risks of sedimentary metal(loid)s in lake ecosystems.

Mechanical properties, degree of sclerotisation and elemental composition of the gastric mill in the red swamp crayfish Procambarus clarkii (Decapoda, Crustacea)

The gastric mill of Decapoda is a unique feature, which comprises teeth, stabilizing ossicles, and particle sorting setae. Involved in the fragmentation and sorting of the food, this structure serves as interface between the organism and its environment. As material properties complement morphology and hold information about function and trophic preferences, we here provide a basis for more comparative research on gastric mills. For gastric mill components of the adult red swamp crayfish Procambarus clarkii, we studied (a) the micro-structure via scanning electron microscopy, (b) the elemental composition by energy-dispersive X-ray spectroscopy, (c) the heterogeneities in material properties and degree of tanning (autofluorescence) by confocal laser scanning microscopy, and (d) the mechanical properties hardness and elasticity by nanoindentation technique. The morphology and micro-structure were previously described for this species, but the mechanical properties and the autofluorescence were not studied before. As epicuticle and exocuticle could be analyzed individually, material property gradients, with values decreasing from the interacting surface towards interior, could be determined. Finally, we were able to relate the mechanical property data with the elemental composition and the degree of tanning. We found that the epicuticle of the teeth is among the hardest and stiffest biological materials in invertebrates due to the incorporations of high proportions of silicon.

Infection with white spot syndrome virus affects the microbiota in the stomachs and intestines of kuruma shrimp

Maintaining eubiosis of the gastrointestinal (GI) microbiota is essential for animal health. White spot syndrome virus (WSSV) is the most lethal viral pathogen because it causes extremely high mortality in shrimp farming. However, it remains poorly understood how WSSV infection affects the microbiota in different regions of the GI tract of shrimp. In the present study, we established an experimental model of kuruma shrimp (Marsupenaeus japonicus) infection with WSSV and then investigated the effects of WSSV infection on the microbiota in the cardiac stomach, pyloric stomach, and intestines using metataxonomics. We identified 34 phyla and 576 genera of bacteria collectively. At the phylum level, Proteobacteria and Firmicutes were the most abundant in all the three GI segments. The WSSV infection decreased microbial diversity to a different extent in the stomachs and in a time-dependent manner. The infection with WSSV affected the microbiota composition in the two stomachs, but not the intestines. Firmicutes increased significantly, while Actinobacteria, Bacteroidetes, and Cyanobacteria decreased in the two stomachs of the WSSV-infected shrimp. At the genus level, Trichococcus and Vibrio increased, but Bradyrhizobium and Roseburia decreased in the cardiac stomach of the WSSV-infected shrimp. Trichococcus and Photobacterium increased in the pyloric stomach. Although Vibrio showed a slight downward trend, Aliivibrio (formerly Vibrio) increased in the pyloric stomach. Thiothrix, Fusibacter, and Shewanella decreased in the pyloric stomach, but no significant differences in these genera were detected in the cardiac stomach. Analysis of the predicted functions of the GI microbiota indicated that the WSSV infection resulted in losses of some microbiota functions. The new information from this study may help better understand the bacteria-virus interaction in the GI tract of shrimp and other crustacean species, and inform pathogen prevention/control and sustainable aquaculture production.

Microplastics in decapod crustaceans: Accumulation, toxicity and impacts, a review

The presence of microplastics in the aquatic environment poses a serious threat not only to aquatic organisms but also to human beings that consume them. The uptake and effects of microplastics have been studied in almost all groups of aquatic organisms. This review details the different aspects of microplastics exposure in an ecologically and economically important group of crustaceans, the Decapods. A majority of Decapod crustaceans such as prawns, shrimp, crabs, lobsters and crayfish are consumed as seafood and play important roles in food chains and food webs. Numerous studies are available on the accumulation of microplastics in tissues such as the gills, hepatopancreas and gastrointestinal tract in these organisms. Experimental studies have also highlighted the toxic effects of microplastics such as oxidative stress, immunotoxicity and reproductive and developmental toxicity in them. This review also summarizes the ecological impacts and implications in human beings as well as lacunae with regard to microplastic uptake in Decapods.

Characterization of 3 different types of aquaporins in Carcinus maenas and their potential role in osmoregulation

Intertidal crustaceans like Carcinus maenas shift between an osmoconforming and osmoregulating state when inhabiting full-strength seawater and dilute environments, respectively. While the bodily fluids and environment of marine osmoconformers are approximately isosmotic, osmoregulating crabs inhabiting dilute environments maintain their bodily fluid osmolality above that of their environment by actively absorbing and retaining osmolytes (e.g., Na⁺, Cl^-, urea) while eliminating excess water. Few studies have investigated the role of aquaporins (AQPs) in the osmoregulatory organs of crustaceans, especially within brachyuran species. In the current study, three different aquaporins were identified within a transcriptome of C. maenas, including a classical AQP (CmAQP1), an aquaglyceroporin (CmGLP1), and a big-brain protein (CmBIB1), all of which are expressed in the gills and the antennal glands. Functional expression of these aquaporins confirmed water transport capabilities for CmAQP1, CmGLP1, but not for CmBIB1, while CmGLP1 also transported urea. Higher relative CmAQP1 mRNA expression within tissues of osmoconforming crabs suggests the apical/sub-apically localized channel attenuates osmotic gradients created by non-osmoregulatory processes while its downregulation in dilute media reduces the water permeability of tissues to facilitate osmoregulation. Although hemolymph urea concentrations rose upon exposure to brackish water, urea was not detected in the final urine. Due to its urea-transport capabilities, CmGLP1 is hypothesized to be involved in a urea retention mechanism believed to be involved in the production of diluted urine. Overall, these results suggest that AQPs are involved in osmoregulation and provide a basis for future mechanistic studies investigating the role of AQPs in volume regulation in crustaceans.

European Lobster Larval Development and Fitness Under a Temperature Gradient and Ocean Acidification

Climate change combined with anthropogenic stressors (e.g. overfishing, habitat destruction) may have particularly strong effects on threatened populations of coastal invertebrates. The collapse of the population of European lobster (Homarus gammarus) around Helgoland constitutes a good example and prompted a large-scale restocking program. The question arises if recruitment of remaining natural individuals and program-released specimens could be stunted by ongoing climate change. We examined the joint effect of ocean warming and acidification on survival, development, morphology, energy metabolism and enzymatic antioxidant activity of the larval stages of the European lobster. Larvae from four independent hatches were reared from stage I to III under a gradient of 10 seawater temperatures (13–24°C) combined with moderate (∼470 µatm) and elevated (∼1160 µatm) seawater pCO2 treatments. Those treatments correspond to the shared socio-economic pathways (SSP), SSP1-2.6 and SSP5-8.5 (i.e. the low and the very high greenhouse gas emissions respectively) projected for 2100 by the Intergovernmental Panel on Climate Change. Larvae under the elevated pCO2 treatment had not only lower survival rates, but also significantly smaller rostrum length. However, temperature was the main driver of energy demands with increased oxygen consumption rates and elemental C:N ratio towards warmer temperatures, with a reducing effect on development time. Using this large temperature gradient, we provide a more precise insight on the aerobic thermal window trade-offs of lobster larvae and whether exposure to the worst hypercapnia scenario may narrow it. This may have repercussions on the recruitment of the remaining natural and program-released specimens and thus, in the enhancement success of future lobster stocks.

Regulation of Drosophila oviduct muscle contractility by octopamine

Octopamine is essential for egg-laying in Drosophila melanogaster, but the neuronal pathways and receptors by which it regulates visceral muscles in the reproductive tract are not known. We find that the two octopamine receptors that have been previously implicated in egg-laying–OAMB and Octβ2R-are expressed in octopaminergic and glutamatergic neurons that project to the reproductive tract, peripheral ppk(+) neurons within the reproductive tract and epithelial cells that line the lumen of the oviducts. Further optogenetic and mutational analyses indicate that octopamine regulates both oviduct contraction and relaxation via Octβ2 and OAMB respectively. Interactions with glutamatergic pathways modify the effects of octopamine. Octopaminergic activation of Octβ2R on glutamatergic processes provides a possible mechanism by which octopamine initiates lateral oviduct contractions. We speculate that aminergic pathways in the oviposition circuit may be comparable to some of the mechanisms that regulate visceral muscle contractility in mammals.

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The receptors Octβ2 and OAMB mediate oviduct muscle contraction and relaxation

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The receptors are detectably expressed in neurons and epithelia but not muscle cells

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The control of visceral muscles in flies and mammals may share common features

Postprandial nitrogen and acid-base regulation in the seawater acclimated green crab, Carcinus maenas

The effects of feeding (meal of 3% of body mass) on acid-base and nitrogen homeostasis were investigated in the seawater acclimated green shore crab, Carcinus maenas. Feeding did not change gastric fluid pH (~pH 6); however, feeding was associated with a respiratory acidosis. Hemolymph HCO₃^- did not increase during this acidosis, although titratable and net acid efflux changed from an uptake to an excretion. Feeding affected the crabs' nitrogen homeostasis causing a substantial increase in hemolymph ammonia and urea concentrations after six hours. At this point, hemolymph urea accounted for ~1/3 of nitrogenous waste accumulated within the hemolymph, suggesting a potential role in ammonia detoxification. The postprandial increase in hemolymph ammonia coincided with an 18-fold increase in ammonia excretion rates that accounted for the majority of net acid excreted by the crabs. Urea excretion rates did not increase after feeding; however, branchial urease activity increased, implying that the gills may possess a mechanism to form excretable ammonia through the catabolism of urea. Our results demonstrate that despite an acidic gastric compartment, C. maenas does not experience a postprandial alkaline tide and that any feeding related acid-base challenges are primarily derived from metabolic acid production. Our findings also indicate that unlike the bicarbonate buffering acid-base compensatory response induced by hypercapnia and emersion, acid-base challenges upon feeding are compensated through changes in the excretion of acid equivalents, mainly in the form of ammonia.

Ecological and potential socioeconomic impacts of two globally-invasive crayfish

Quantifying the impacts of invasive species, relative to native analogues, is crucial for management and policy development. Two freshwater crayfish species of global concern, Cherax quadricarinatus and Procambarus clarkii, have established populations across Africa. Negative impacts on native biodiversity and socioeconomic impacts have been documented in other continents; however, there is a paucity of information on impacts from Africa and for C. quadricarinatus. To fill this literature gap, this study used laboratory experiments to determine potential ecological and socioeconomic impacts conferred by the crayfish species relative to a functionally similar native analogue, the river crab Potamonautes perlatus, on two static, but different resources. Consumption rates were derived for the three focal species consuming the macrophyte Potamogeton nodosus and dead Oreochromis mossambicus under different temperatures regimes (19 °C and 28 °C), representing summer and winter seasons in Southern Africa, with maximum feeding rate used to infer impact. Potamogeton represents ecologically-important nutrient cycling macrophytes, as well as crucial habitat for juvenile fish, whereas dead O. mossambicus was used as proxy for fish catches in artisanal gillnet fisheries often scavenged by crayfish. Consumption of both resources by all the decapods increased with temperature. However, the two invasive crayfish showed different impact trends where P. clarkii had a significantly higher consumption of macrophytes than the other two decapods regardless of temperature and the same trends seen, but for C. quadricarinatus scavenging on fish. Crayfish introductions clearly have potential for highly destructive ecological and socioeconomic impacts to invaded systems as compared to the native crabs. The disparity between resource use emphasises the necessity to use appropriate geographical and species-specific contexts to avoid erroneous conclusions from generalised risk assessments. Derived feeding rates can be used for rapid impact assessments and comparisons in other invasion cores.

Protein sources influence both apparent digestibility and gastrointestinal evacuation rate in juvenile slipper lobster (Thenus australiensis)

Apparent digestibility and gastrointestinal evacuation rate were measured to assess the potential of five commercially available protein sources for their inclusion in feeds for juvenile slipper lobster, Thenus australiensis. Protein sources tested were fishmeal, krill meal, lupin meal, soybean meal and squid by-product meal. Apparent digestibility of crude protein ranged from 79.6% to 95.3%, with fishmeal protein significantly less digestible than lupin meal, squid by-product meal and soybean meal. Gastrointestinal evacuation rate was estimated from marker replacement, where yttrium oxide replaced ytterbium oxide. Faeces were collected every 3 h for 48 h, and a kinetic model was used to calculate the rate and time for the second marker to replace the first marker. Gastrointestinal evacuation (≥ 95%) was completed between 4 and 6 h with no significant differences among protein sources. Faeces consisted of both markers in equal parts 2.7 to 5.0 h after the feed switch, with lupin meal reaching the midpoint significantly faster than squid by-product meal and reference feed. The present study is the first in crustaceans to examine the relationship between apparent digestibility and gastrointestinal evacuation, showing more digestible protein sources had slower evacuation rates. The combined approach provides deeper insight into crustaceans' digestive physiology and helps understand their ability to digest specific ingredients. Further research is recommended to understand protein requirements in a broader context to verify highly digestible protein sources meet all nutritional requirements.

Feeding state-dependent modulation of feeding-related motor patterns

Studies elucidating modulation of microcircuit activity in isolated nervous systems have revealed numerous insights regarding neural circuit flexibility, but this approach limits the link between experimental results and behavioral context. To bridge this gap, we studied feeding behavior-linked modulation of microcircuit activity in the isolated stomatogastric nervous system (STNS) of male Cancer borealis crabs. Specifically, we removed hemolymph from a crab that was unfed for ≥24 h ("unfed" hemolymph) or fed 15 min to 2 h before hemolymph removal ("fed" hemolymph). After feeding, the first significant foregut emptying occurred >1 h later and complete emptying required ≥6 h. We applied the unfed or fed hemolymph to the stomatogastric ganglion (STG) in an isolated STNS preparation from a separate, unfed crab to determine its influence on the VCN (ventral cardiac neuron)-triggered gastric mill (chewing) and pyloric (filtering of chewed food) rhythms. Unfed hemolymph had little influence on these rhythms, but fed hemolymph from each examined time-point (15 min, 1 h, or 2 h after feeding) slowed one or both rhythms without weakening circuit neuron activity. There were also distinct parameter changes associated with each time-point. One change unique to the 1-h time-point (i.e., reduced activity of one circuit neuron during the transition from the gastric mill retraction to protraction phase) suggested that the fed hemolymph also enhanced the influence of a projection neuron that innervates the STG from a ganglion isolated from the applied hemolymph. Hemolymph thus provides a feeding state-dependent modulation of the two feeding-related motor patterns in the C. borealis STG.NEW & NOTEWORTHY Little is known about behavior-linked modulation of microcircuit activity. We show that the VCN-triggered gastric mill (chewing) and pyloric (food filtering) rhythms in the isolated crab Cancer borealis stomatogastric nervous system were changed by applying hemolymph from recently fed but not unfed crabs. This included some distinct parameter changes during each examined post-fed hemolymph time-point. These results suggest the presence of feeding-related changes in circulating hormones that regulate consummatory microcircuit activity.

Toward a More Comprehensive View of α-Amylase across Decapods Crustaceans

Decapod crustaceans are a very diverse group and have evolved to suit a wide variety of diets. Alpha-amylases enzymes, responsible for starch and glycogen digestion, have been more thoroughly studied in herbivore and omnivore than in carnivorous species. We used information on the α-amylase of a carnivorous lobster as a connecting thread to provide a more comprehensive view of α-amylases across decapods crustaceans. Omnivorous crustaceans such as shrimps, crabs, and crayfish present relatively high amylase activity with respect to carnivorous crustaceans. Yet, contradictory results have been obtained and relatively high activity in some carnivores has been suggested to be a remnant trait from ancestor species. Here, we provided information sustaining that high enzyme sequence and overall architecture conservation do not allow high changes in activity, and that differences among species may be more related to number of genes and isoforms, as well as transcriptional and secretion regulation. However, recent evolutionary analyses revealed that positive selection might have also occurred among distant lineages with feeding habits as a selection force. Some biochemical features of decapod α-amylases can be related with habitat or gut conditions, while less clear patterns are observed for other enzyme properties. Likewise, while molt cycle variations in α-amylase activity are rather similar among species, clear relationships between activity and diet shifts through development cannot be always observed. Regarding the adaptation of α-amylase to diet, juveniles seem to exhibit more flexibility than larvae, and it has been described variation in α-amylase activity or number of isoforms due to the source of carbohydrate and its level in diets, especially in omnivore species. In the carnivorous lobster, however, no influence of the type of carbohydrate could be observed. Moreover, lobsters were not able to fine-regulate α-amylase gene expression in spite of large changes in carbohydrate content of diet, while retaining some capacity to adapt α-amylase activity to very low carbohydrate content in the diets. In this review, we raised arguments for the need of more studies on the α-amylases of less studied decapods groups, including carnivorous species which rely more on dietary protein and lipids, to broaden our view of α-amylase in decapods crustaceans.

Longitudinal variations in the gastrointestinal microbiome of the white shrimp, Litopenaeus vannamei

The shrimp gut is a long digestive structure that includes the Foregut (stomach), Midgut (hepatopancreas) and Hindgut (intestine). Each component has different structural, immunity and digestion roles. Given these three gut digestive tract components' significance, we examined the bacterial compositions of the Foregut, Hindgut, and Midgut digestive fractions. Those bacterial communities' structures were evaluated by sequencing the V3 hypervariable region of the 16S rRNA gene, while the functions were predicted by PICRUSt2 bioinformatics workflow. Also, to avoid contamination with environmental bacteria, shrimp were maintained under strictly controlled conditions. The pairwise differential abundance analysis revealed differences among digestive tract fractions. The families Rhodobacteraceae and Rubritalaceae registered higher abundances in the Foregut fraction, while in the Midgut, the families with a higher proportion were Aeromonadaceae, Beijerinckiaceae and Propionibacteriaceae. Finally, the Cellulomonadaceae family resulted in a higher proportion in the Hindgut. Regarding the predicted functions, amino acid and carbohydrate metabolism pathways were the primary functions registered for Foregut microbiota; conversely, pathways associated with the metabolism of lipids, terpenoids and polyketides, were detected in the Midgut fraction. In the Hindgut, pathways like the metabolism of cofactors and vitamins along with energy metabolism were enriched. Structural changes were followed by significant alterations in functional capabilities, suggesting that each fraction's bacteria communities may carry out specific metabolic functions. Results indicate that white shrimp's gut microbiota is widely related to the fraction analyzed across the digestive tract. Overall, our results suggest a role for the dominant bacteria in each digestive tract fraction, contributing with a novel insight into the bacterial community.

Biological Impact of Photoperiod on Fairy Shrimp (Branchinecta orientalis): Life History and Biochemical Composition

Simple Summary

Branchinecta orientalis G.O. Sars, 1901 is a broadly distributed fairy shrimp species in temporary freshwater pools throughout Europe and Asia. Recently, using fairy shrimps to feed freshwater fish and shellfish species has been brought to attention mainly due to their high nutritional value, possibility of mass culture, and ability to remain alive for long periods when used as prey. Fairy shrimps might be valuable alternatives for the widely used brine shrimp Artemia species; however, relatively little is known regarding their life-cycle characteristics and biochemical properties under various environmental conditions. Among environmental factors, the photoperiod is assumed as an important environmental cue to regulate the growth, development, and physio-biochemical properties of animals. In the present study, the growth performances, reproductive status, and nutritional quality of fairy shrimp were investigated under predefined environmental conditions, i.e., different photoperiods, and compared with various common live prey used in freshwater ornamental fish production.

Abstract

B. orientalis, fairy shrimp, is often among the most conspicuous invertebrates inhabiting temporary aquatic habitats with a typical variation in environmental conditions. Its life history characteristics and biochemical composition were studied under four different photoperiodic regimes (24L:0D, 0L:24D, 16L:8D, and 12L:12D). The significantly highest cumulative and initial hatching rates (48 h) were obtained at 24L:0D (p < 0.05). Cultivating the larvae under different photoperiods did not significantly affect specific growth rate (SGR) (p > 0.05). However, higher final total body length and daily growth rate were recorded under constant darkness. Higher lipid content was found at 24L:0D to the extent that it was more than two times higher than that at 16L:8D and 12L:12D (p < 0.05). There was also a remarkable increase in body crude protein content at 24L:0D (p < 0.05). Body fatty-acid profiles of the fairy shrimps were also affected by culture condition (p < 0.05). Extension of lighting period resulted in a subtle increase in body contents of arginine, lysine, histidine, isoleucine, leucine, valine, methionine, and phenylalanine, especially in the group kept under a 16L:8D regime. The highest and lowest digestive enzyme activity was observed at 0L:24D and 24L:0D, respectively (p < 0.05). In contrast, the highest and lowest soluble protein content was recorded at 24L:0D and 0L:24D, respectively (p < 0.05). Similarly, antioxidant status was significantly higher at 0L:24D (p < 0.05). In conclusion, a 16L:8D light–dark cycle might be an optimal condition in terms of growth performance and physio-biochemical characteristics. These findings could be helpful in optimizing the rearing conditions for upscaling B. orientalis production.

Synthesis of digestive enzymes, food processing, and nutrient absorption in decapod crustaceans: a comparison to the mammalian model of digestion

The ∼15.000 decapod crustaceans that are mostly omnivorous have evolved a structurally and functionally complex digestive system. They have highly effective cuticular chewing and filtering structures in the stomach, which are regularly renewed by moulting. Decapods produce a broad range of digestive enzymes including chitinases, cellulases, and collagenases with unique properties. These enzymes are synthesized in the F-cells of the hepatopancreas and are encoded in the genome as pre-pro-proteins. In contrast to mammals, they are stored in a mature form in the lumen of the stomach to await the next meal, and therefore, the enzymes are particularly stable. The fat emulsifiers are fatty acyl-dipeptides rather than bile salts. After mechanical and chemical processing of the food in the cardiac stomach, the chyme is filtered by two unique filter systems of different mesh-size. The filtrate is then transferred to the hepatopancreas where the nutrients are absorbed by the R-cells, mostly via carriers, resembling nutrient absorption in the small intestine of mammals. The absorbed nutrients are used to fuel the metabolism of the hepatopancreas, are supplied to other organs, and are stored in the R-cells as glycogen and lipid reserves. Export lipids are secreted from the R-cells into the haemolymph as high density lipoproteins that mainly consist of phospholipids. In contrast to mammals, the midgut tube and hindgut contribute only little to food processing and nutrient absorption. The oesophagus, stomach and hindgut are well innervated but the hepatopancreas lacks nerves. Hormone cells are abundant in the midgut and hepatopancreas epithelia. Microorganisms are often present in the intestine of decapods, but they are apparently not essential for digestion and nutrition.

Preliminary results on the occurrence and anatomical distribution of microplastics in wild populations of Nephrops norvegicus from the Adriatic Sea

This study reports the shapes, dimensional classes, types and counts of microplastics (MPs) found in 23 individuals of N. norvegicus collected from two wild populations of the Adriatic Sea (Mediterranean basin). The focus was on three different anatomical compartments (gut, hepatopancreas and tail), which were analysed separately. MPs were found in all the investigated individuals with an average of about 17 MPs/individual. Fragments were predominant over fibers with a ratio of about 3:1. The majority of MPs were in the dimensional range 50-100 μm. The predominant polymers were polyester, polyamide 6, polyvinyl chloride and polyethylene, which together constitute about 61% of all the MPs found. Fragments were more concentrated in the hepatopancreas, with no significant difference between gut and tail, while fibers were more concentrated in the gut than in the tail with hepatopancreas somehow in between. The dimensional class of the MPs influences their anatomical distribution. There were no statistical differences among individuals from the two sampling sites. Sex of the individual did not influence the level of retained MPs, while length had a very marginal effect. The information reported here contributes to understanding of the possible risks linked to human consumption of different tissues from contaminated Norway lobsters.

Mass Spectrometry Quantification, Localization, and Discovery of Feeding-Related Neuropeptides in Cancer borealis

The crab Cancer borealis nervous system is an important model for understanding neural circuit dynamics and modulation, but the identity of neuromodulatory substances and their influence on circuit dynamics in this system remains incomplete, particularly with respect to behavioral state-dependent modulation. Therefore, we used a multifaceted mass spectrometry (MS) method to identify neuropeptides that differentiate the unfed and fed states. Duplex stable isotope labeling revealed that the abundance of 80 of 278 identified neuropeptides was distinct in ganglia and/or neurohemal tissue from fed vs unfed animals. MS imaging revealed that an additional 7 and 11 neuropeptides exhibited altered spatial distributions in the brain and the neuroendocrine pericardial organs (POs), respectively, during these two feeding states. Furthermore, de novo sequencing yielded 69 newly identified putative neuropeptides that may influence feeding state-related neuromodulation. Two of these latter neuropeptides were determined to be upregulated in PO tissue from fed crabs, and one of these two peptides influenced heartbeat in ex vivo preparations. Overall, the results presented here identify a cohort of neuropeptides that are poised to influence feeding-related behaviors, providing valuable opportunities for future functional studies.

Nutrition and Functions of Amino Acids in Aquatic Crustaceans

Crustaceans (e.g., shrimp and crabs) are a good source of protein-rich foods for human consumption. They are the second largest aquaculture species worldwide. Understanding the digestion of dietary protein, as well as the absorption, metabolism and functions of amino acids (AAs) and small peptides is essential to produce cost-effective and sustainable aquafeeds. Hepatopancreas (the midgut gland) is the main site for the digestion of dietary protein as well as the absorption of small peptides and AAs into the hemolymph. Besides serving as the building blocks of protein, AAs (particularly aspartate, glutamate, glutamine and alanine) are the primary metabolic fuels for the gut and extra-hepatopancreas tissues (e.g., kidneys and skeletal muscle) of crustaceans. In addition, AAs are precursors for the syntheses of glucose, lipids, H₂S, and low-molecular-weight molecules (e.g., nitric oxide, glutathione, polyamines, histamine, and hormones) with enormous biological importance, such as physical barrier, immunological and antioxidant defenses. Therefore, both nutritionally essential and nonessential AAs are needed in diets to improve the growth, development, molt rate, survival, and reproduction of crustaceans. There are technical difficulties and challenges in the use of crystalline AAs for research and practical production due to the loss of free AAs during feed processing, the leaching of in-feed free AAs to the surrounding water environment, and asynchronous absorption with peptide-bounded AAs. At present, much knowledge about AA metabolism and functions in crustaceans is based on studies of mammals and fish species. Basic research in this area is necessary to lay a solid foundation for improving the balances and bioavailability of AAs in the diets for optimum growth, health and wellbeing of crustaceans, while preventing and treating their metabolic diseases. This review highlights recent advances in AA nutrition and metabolism in aquatic crustacean species at their different life stages. The new knowledge is expected to guide the development of the next generation of their improved diets.

High prevalence of plastic ingestion by Eriocheir sinensis and Carcinus maenas (Crustacea: Decapoda: Brachyura) in the Thames Estuary

This study presents evidence for microplastic contamination in two resident species of brachyuran crab from the Thames Estuary: the native shore crab, Carcinus maenas (Linneaus, 1758) and the invasive Chinese mitten crab, Eriocheir sinensis (H. Milne Edwards, 1853). The gills, gastric mill and intestine of 94 C. maenas and 41 E. sinensis were examined. Crabs were sampled periodically (ca. every three months) between December 2018 and October 2019. A total of 874 plastics were recovered, ranging 34 μm-34 mm in length. Overall, 71.3% and 100% of C. maenas and E. sinensis, respectively, contained at least one item (fibre, film, fragment or tangle of fibres) in the gill chamber, gastric mill or gastrointestinal tract. The most common items were fibres (78.5%) but in some cases, particularly in the gastric mill, these were aggregated into tangles (7.8%). Almost all E. sinensis contained tangles of fibres (95.1%), whereas, relatively few C. maenas contained similar tangles (10.6%).

Can Cephalopods Vomit? Hypothesis Based on a Review of Circumstantial Evidence and Preliminary Experimental Observations

In representative species of all vertebrate classes, the oral ejection of upper digestive tract contents by vomiting or regurgitation is used to void food contaminated with toxins or containing indigestible material not voidable in the feces. Vomiting or regurgitation has been reported in a number of invertebrate marine species (Exaiptasia diaphana, Cancer productus, and Pleurobranchaea californica), prompting consideration of whether cephalopods have this capability. This "hypothesis and theory" paper reviews four lines of supporting evidence: (1) the mollusk P. californica sharing some digestive tract morphological and innervation similarities with Octopus vulgaris is able to vomit or regurgitate with the mechanisms well characterized, providing an example of motor program switching; (2) a rationale for vomiting or regurgitation in cephalopods based upon the potential requirement to void indigestible material, which may cause damage and ejection of toxin contaminated food; (3) anecdotal reports (including from the literature) of vomiting- or regurgitation-like behavior in several species of cephalopod (Sepia officinalis, Sepioteuthis sepioidea, O. vulgaris, and Enteroctopus dofleini); and (4) anatomical and physiological studies indicating that ejection of gastric/crop contents via the buccal cavity is a theoretical possibility by retroperistalsis in the upper digestive tract (esophagus, crop, and stomach). We have not identified any publications refuting our hypothesis, so a balanced review is not possible. Overall, the evidence presented is circumstantial, so experiments adapting current methodology (e.g., research community survey, in vitro studies of motility, and analysis of indigestible gut contents and feces) are described to obtain additional evidence to either support or refute our hypothesis. We recognize the possibility that further research may not support the hypothesis; therefore, we consider how cephalopods may protect themselves against ingestion of toxic food by external chemodetection prior to ingestion and digestive gland detoxification post-ingestion. Reviewing the evidence for the hypothesis has identified a number of gaps in knowledge of the anatomy (e.g., the presence of sphincters) and physiology (e.g., the fate of indigestible food residues, pH of digestive secretions, sensory innervation, and digestive gland detoxification mechanisms) of the digestive tract as well as a paucity of recent studies on the role of epithelial chemoreceptors in prey identification and food intake.

Environmental rearing conditions are key determinants of changes in immune gene expression patterns in shrimp midgut

The super-intensive BioFloc Technology (BFT) system has been highlighted as a promising eco-friendly alternative to the traditional shrimp rearing systems. To gain insight into the impact of environmental rearing conditions on shrimp intestinal immunity, we assessed the expression profile of key immunological genes in the midgut of Litopenaeus vannamei shrimp reared in two contrasting culture systems: the indoor super-intensive BFT and the outdoor intensive Green-Water System (GWS). From the 30 analyzed genes, the expression levels of 25 genes were higher in the midgut of shrimp reared in BFT than in GWS. The main functional categories represented in BFT-shrimp were the prophenoloxidase-activating system, immune signaling, antimicrobial peptides, and RNA interference pathway. Comparatively, only the RNAi pathway gene Dicer-1 (LvDcr1) was more expressed in animals from the GWS group. However, despite the differences in gene expression, the total midgut bacterial abundance was similar between the experimental groups. Altogether, our results suggest that the microbial-rich environment offered by the BFT system can be acting as an immunostimulant by altering the immune expression profile of the midgut. The gene expression level found in GWS animals could be related to the chronic presence of the IMNV in the Brazilian Northeast. Knowing the effects of environmental stress factors on the intestinal immune defenses can provide an in-depth understanding of the relationship between cultivated shrimp and the major pathogens affecting the shrimp industry.

How to get rid of ingested microplastic fibers? A straightforward approach of the Atlantic ditch shrimp Palaemon varians

Microplastic fibers represent a significant share of the global marine micrcroplastic pollution, particularly in coastal areas. In controlled laboratory experiments, we offered fluorescent microplastic fibers (40-4400 μm lengths, median 150 μm) and spherical microplastic beads (9.9 μm Ø) together with commercial fish food to the Atlantic ditch shrimp Palaemonetes varians. The shrimps ingested fibers and beads along with the food. Upon ingestion, the beads and the shortest fibers (up to 100 μm) passed from the stomach into the gut and were egested within the fecal strings. The longer fibers first remained in the stomach but were regurgitated, i.e. extruded through the esophagus, within 12-14 h. Regurgitation is an evolutionary adaptation of particular crustacean species and other invertebrates to remove large and indigestible food particles from the stomach. Accordingly, the process of regurgitation attained a new task nowadays, i.e. the elimination of anthropogenic filamentous microplastic debris from the stomach to avoid harm. This behavioral feature may represent a selective advantage in view of the continuously increasing environmental plastic pollution.

Changes in precipitation may alter food preference in an ecosystem engineer, the black land crab, Gecarcinus ruricola

Gecarcinid land crabs are ecosystem engineers playing an important role in nutrient recycling and seedling propagation in coastal forests. Given a predicted future decline in precipitation for the Caribbean, the effects of dehydration on feeding preferences of the black land crab Gecarcinus ruricola were investigated. G. ruricola were offered novel food items of lettuce, apple, or herring to test for food choice based on water and nutritional (energetic) content in single and multiple choice experimental designs. The effect of dehydration was incorporated by depriving crabs of water for 0, 4, or 8 days, leading to an average body water loss of 0%, 9%, and 17%, respectively, (crabs survived a body water loss of 23% + 2% and 14-16 days without access to water). The results were consistent between the single and multiple choice experiments: crabs consumed relatively more apple and fish and only small amounts of lettuce. Overall, no selective preferences were observed as a function of dehydration, but crabs did consume less dry food when deprived of water and an overall lower food intake with increasing dehydration levels occurred. The decrease in feeding was likely due to loss of water from the gut resulting in the inability to produce ample digestive juices. Future climatic predictions suggest a 25-50% decline in rainfall in the Caribbean, which may lead to a lower food intake by the crabs, resulting in compromised growth. The subsequent reduction in nutrient recycling highlights possible long-term effects on coastal ecosystems and highlights the importance of future work on climate relative behavioral interactions that influence ecosystem function.

The gastric sieve of penaeid shrimp species is a sub-micrometer nutrient filter

Unlike that of vertebrates, the penaeid shrimp stomach is of ectodermic origin and is thus covered by a cuticle that is sloughed upon molting. It is composed of two chambers, here called the anterior and posterior stomach chambers, ASC and PSC, respectively. The PSC contains a filtration structure variously called a pyloric filter, filter press, gastric filter or gastric sieve (GS), and the last of these will be used here. The GS resembles an elongated, inverted-V, dome-like, chitinous structure with a midline ridge that is integral to the ventral base of the PSC. The dome surface is covered with a carpet-like layer of minute, comb-like setae bearing laterally branching setulae. This carpet serves as a selective filter that excludes large partially digested food particles but allows smaller particles and soluble materials to enter hepatopancreatic ducts that conduct them into the shrimp hepatopancreas (HP), where further digestion and absorption of nutrients takes place. Although the GS function is well known, its exclusion limit for particulate material has not been clearly defined. Using histological and ultra-structure analysis, we show that the GS sieve pore diameter is approximately 0.2-0.7 µm in size, indicating a size exclusion limit of substantially less than 1 µm. Using fluorescent microbeads, we show that particles of 1 µm diameter could not pass through the GS but that particles of 0.1 µm diameter did pass through to accumulate in longitudinal grooves and move on to the HP, where some were internalized by tubule epithelial cells. We found no significant difference in these sizes between the species Penaeus monodon and Penaeus vannamei or between juveniles and adults in P. vannamei This information will be of value for the design of particulate feed ingredients such as nutrients, therapeutic drugs and toxin-absorbing materials that may selectively target the stomach, intestine or HP of cultivated shrimp.

Litopenaeus vannamei stylicins are constitutively produced by hemocytes and intestinal cells and are differentially modulated upon infections

Stylicins are anionic antimicrobial host defense peptides (AAMPs) composed of a proline-rich N-terminal region and a C-terminal portion containing 13 conserved cysteine residues. Here, we have increased our knowledge about these unexplored crustacean AAMPs by the characterization of novel stylicin members in the most cultivated penaeid shrimp, Litopenaeus vannamei. We showed that the L. vannamei stylicin family is composed of two members (Lvan-Stylicin1 and Lvan-Stylicin2) encoded by different loci which vary in gene copy number. Unlike the other three gene-encoded antimicrobial peptide families from penaeid shrimp, the expression of Lvan-Stylicins is not restricted to hemocytes. Indeed, they are also produced by the columnar epithelial cells lining the midgut and its anterior caecum. Interestingly, Lvan-Stylicins are simultaneously transcribed at different transcriptional levels in a single shrimp and are differentially modulated in hemocytes after infections. While the expression of both genes showed to be responsive to damage-associated molecular patterns, only Lvan-Stylicin2 was induced after a Vibrio infection. Besides, Lvan-Stylicins also showed a distinct pattern of gene expression in the three portions of the midgut (anterior, middle and posterior) and during shrimp development. We provide here the first evidence of the diversity of the stylicin antimicrobial peptide family in terms of sequence and gene expression distribution and regulation.