Effect of stocking density on growth performance, digestive enzyme activities, and nonspecific immune parameters of Palaemonetes sinensis

The Protective Effect of a Dietary Extract of Mulberry (Morus alba L.) Leaves against a High Stocking Density, Copper and Trichlorfon in Crucian Carp (Carassius auratus)

This study was designed to examine the protective effects of the extract of mulberry (Morus alba L.) leaves (EML) on crucian carp (Carassius auratus) against a high stocking density, Cu exposure and trichlorfon exposure, which adversely impact fish growth performance, feed intake and fish locomotion. High stocking densities decreased the activities of amylase, lipase, trypsin, Na+/K+-ATPase and alkaline phosphatase (AKP), and increased the content of malonaldehyde (MDA) in fish digestive organs, indicating an impairment of the digestive function and a disturbance of the antioxidant status. Cu exposure increased the activities of glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) in fish digestive organs, suggesting the activation of amino acid metabolism. Furthermore, trichlorfon exposure reduced the activities of lactate dehydrogenase (LDH), glutathione reductase (GR), GOT and GPT, and the capacities of the anti-superoxide anion (ASA) and anti-hydroxyl radical (AHR) in fish muscles, indicating a disruption of the bioenergetic homeostasis and antioxidant status. Our present study indicates that dietary EML supplementation relieved the detrimental effects induced by these stressors.

Scoparia dulcis L. Extract Relieved High Stocking Density-Induced Stress in Crucian Carp (Carassius auratus)

The objective of this study was to investigate the effects of Scoparia dulcis extract (SDE) on stress induced by high stocking density and Cu and trichlorfon exposure in crucian carp (Carassius auratus). The results showed that these stressors exerted detrimental effects in fish, such as inhibition of growth performance, reduced feed intake, and interruption of fish locomotion. Under high stocking density, dietary SDE supplementation increased the content of reduced glutathione (GSH) and the activities of amylase, catalase (CAT), and glutathione reductase (GR) and decreased the content of malonaldehyde (MDA) in the intestine of crucian carp. A similar trend was presented in the hepatopancreas under Cu exposure. Dietary SDE supplementation enhanced the activities of CAT, superoxide dismutase (SOD), glutathione peroxidase (GPx), lactate dehydrogenase, glutamate-oxaloacetate transaminase, and glutamate-pyruvate transaminase in the muscle of crucian carp under trichlorfon exposure. The optimum dietary SDE supplementation levels were 4.07, 4.33, and 3.95 g kg-1 diet based on the recovery rate of weight gain (RWG), feed intake (FI), and inhibitory rate of rollover (IR) for crucian carp under high stocking density and Cu and trichlorfon exposure, respectively. Overall, dietary supplementation with SDE may be a useful nutritional strategy for relieving these stresses in aquatic animals.

Biofloc technology and immune response of penaeid shrimp: A meta-analysis and meta-regression

Biological flocs develop as heterogenious communities of detritus, heterotrophic and autotrophic bacteria, algae, fungi and a variety of other things through appropriate management of the carbon-nitrogen ratio in aquaculture farming systems. These microbial communities improve the water quality, reduce the concentrations of toxic inorganic species, and act as a source of food and immunostimulants. However, the information about their role as immunostimulants is widely variable. To obtain a clearer view of the situation, it is necessary to summarize the current literature on this topic through a quantitative review analysis: a meta-analysis. The present work aims to evaluate the effect of biofloc technology (BFT) implementation on culture water quality through meta-analysis, meta-regression, and correlation analysis. Pubmed, Science Direct, Scopus, and Google Scholar were searched from 2000 to 2022 on the influence of BFT on immunological parameters. Three hundred and thirty-four of the scientific articles used BFT for penaeid shrimp, but only 25 articles met the inclusion criterion of using BFT to evaluate its effect on the shrimp's immunity. The current analysis found that the use of BFT stimulates all the evaluated immunological parameters. Also, meta-regression with fixed data of study parameters showed that slow-release carbon sources, probiotics, and an estimated carbon/nitrogen ratio of 10 potentiated a larger effect on BFT immune stimulation. The meta-analysis demonstrated that the volumes of the settleable solids (SS) and the total suspended solids (TSS) are crucial for the effect of BFT on the shrimp immune system. When TSS was higher than 294 mg/L, the respiratory metabolism of the shrimp was compromised. The analysis found evidence of publication biases, indicating that the data had to be interpreted carefully. Nonetheless, this meta-analysis shows that the data quality was sound and the approach used was appropriate; moreover, it also showed that BFT can be an environmentally friendly alternative culture method that enhances the shrimp's immune system.

Effects of Panax notoginseng Water Extract on Immune Responses and Digestive Enzymes in White Shrimp Litopenaeus vannamei

Panax notoginseng (Burk) F. H. Chen is a traditional Chinese herbal medicine commonly used in clinical applications. This study examined the effects of the Panax notoginseng water extract (PNWE) on the immune responses and digestive enzyme activity of Litopenaeus vannamei (L. vannamei). The PNWE (50, 100, and 200 μg (g shrimp)^-1) was injected into L. vannamei to analyze the immune response parameters, including the total haemocyte count (THC), granular haemocytes (GC), semi-granular haemocytes (SGC), hialin haemocyte (HC), the respiratory burst (RB), the phagocytic ratio (PR), the phagocytic index (PI), and phenoloxidase (PO). We evaluated the activity of the intestinal digestive enzymes (trypsin, chymotrypsin, amylase, and lipase), the histopathology, and the intestine Vibrio numbers. The results showed that different concentrations of the PNWE significantly increased THC, GC, SGC, PO and RB activity, the PR, and the PI of L. vannamei while reducing the HC. In addition, the PNWE also significantly increased the chymotrypsin, trypsin, and amylase activity of L. vannamei. Furthermore, 50 µg (g shrimp)^-1 of PNWE regulated the lipase activity. Additionally, different concentrations of the PNWE significantly reduced the Vibrio numbers in the intestine without damaging the hepatopancreas and intestine tissues. These results indicate that the PNWE improves the immune responses of L. vannamei by increasing the haemocyte count and regulating intestinal digestive enzymes.

Transcriptomic analysis of male three-spot swimming crab (Portunus sanguinolentus) infected with the parasitic barnacle Diplothylacus sinensis

Diplothylacus sinensis is reported as an intriguing parasitic barnacle that can negatively affect the growth, molting, reproduction in several commercially important portunid crabs. To better understand the molecular mechanisms of host-parasite interactions, we characterized the gene expression profiles from the healthy and D. sinensis infected Portunus sanguinolentus by high-through sequence method. Totally, the transcriptomic analysis generated 52, 266, 600 and 51, 629, 604 high quality reads from the infected and control groups, respectively. The clean reads were assembled to 90,740 and 69,314 unigenes, with the average length of 760 bp and 709 bp, respectively. The expression analysis showed that 18,959 genes were significantly changed by the parasitism of D. sinensis, including 4769 activated genes and 14,190 suppressed genes. The differentially expressed genes were categorized into 258 KEGG pathways and 647 GO terms. The GO analysis mapped 13 DEGs related to immune system process and 32 DEGs related to immune response, respectively, suggesting a potential alteration of transcriptional expression patterns in complement cascades of P. sanguinolentus. Additionally, 4 representative molting-related genes were down-regulated in parasitized group, indicating D. sinensis infection appeared to suppress the producing of ecdysteroid hormones. In conclusion, the present study improves our understanding on parasite-host interaction mechanisms, which focuses the function of Ecdysone receptor, Toll-like receptor and cytokine receptor of crustacean crabs infestation with rhizocephalan parasites.

Resource recovery from fish waste: Prospects and the usage of intensified extraction technologies

Globally, the valorization of fish biowaste as a feedstock to recover valuable components is an emerging research and commercial interest area to achieve the SDG goals by 2030. Fish waste-derived biomolecules are increasingly finding diverse applications in food and other biotechnological fields due to their excellent chemical, structural and functional properties. The focus of this review is to highlight the conventional valorization routes and recent advancements in extraction technologies for resource recovery applications, primarily focusing on green processes. Biointensified processes involving ultrasound, microwave, sub- and supercritical fluids, pulsed electric field, high-pressure processing, and cold plasma are extensively explored as sustainable technologies for valorizing fish discards and found numerous applications in the production of functional and commercially important biomaterials. With challenges in recovering intracellular bioactive compounds, selectivity, and energy requirement concerns, conventional approaches are being relooked continuously in the quest for process intensification and sustainable production practices. Nonetheless, in the context of 'zero waste' and 'biorefinery for high-value compounds', there is immense scope for technological upgradation in these emerging alternative approaches. This work details such attempts, providing insights into the immense untapped potential in this sector.

Stocking density mediated stress modulates growth attributes in cage reared Labeo rohita (Hamilton) using multifarious biomarker approach

The present study was conducted for 240 days to evaluate the effects of stocking density based on growth attributes, digestive enzymes, muscular composition, biochemical and physiological responses of Labeo rohita fingerlings in tropical inland open water cages. L. rohita (30.35 ± 1.08 g) were randomly distributed into three treatments, namely low stocking density, LSD (10 m^-3), medium stocking density, MSD (20 m^-3) and high stocking density, HSD (30 m^-3) in triplicates. Fish were fed twice daily with CIFRI CAGEGROW® floating feed (crude protein-28%, crude fat-4%). Fish growth and feed efficiency were higher (p < 0.05) in LSD, however, MSD registered a higher yield. Amylase and protease activity reduced whereas lipase activity increased with increasing stocking density. Muscle crude protein and crude fat formed an inverse correlation. The fillet quality deteriorated at higher stocking densities based on Muscle pH, drip loss and frozen leakage rate. The stress biomarkers level (glucose, cortisol, superoxide dismutase and catalase) increased in serum under crowding conditions. Glutamate oxaloacetate transaminase and glutamate pyruvate transaminase in serum were significantly increased in HSD. Serum protein levels decreased with the increase in stocking densities. Body ionic imbalance (Na⁺, Cl^- and K⁺) was observed under crowding stress. Based on growth attributes and multiple biomarker responses, L. rohita @ 10 m^-3 was found to be the optimum density for inland open water cage culture.

Segment number threshold determines juvenile onset of germline cluster expansion in Platynereis dumerilii

Development of sexual characters and generation of gametes are tightly coupled with growth. Platynereis dumerilii is a marine annelid that has been used to study germline development and gametogenesis. P. dumerilii has germ cell clusters found across the body in the juvenile worms, and the clusters eventually form the gametes. Like other segmented worms, P. dumerilii grows by adding new segments at its posterior end. The number of segments reflect the growth state of the worms and therefore is a useful and measurable growth state metric to study the growth‐reproduction crosstalk. To understand how growth correlates with progression of gametogenesis, we investigated germline development across several developmental stages. We discovered a distinct transition period when worms increase the number of germline clusters at a particular segment number threshold. Additionally, we found that keeping worms short in segment number, by manipulating environmental conditions or via amputations, supported a segment number threshold requirement for germline development. Finally, we asked if these clusters in P. dumerilii play a role in regeneration (as similar free‐roaming cells are observed in Hydra and planarian regeneration) and found that the clusters were not required for regeneration in P. dumerilii, suggesting a strictly germline nature. Overall, these molecular analyses suggest a previously unidentified developmental transition dependent on the growth state of juvenile P. dumerilii leading to substantially increased germline expansion.

Total segment number predicts the state of germline development and the abundance of germline clusters in Platynereis dumerilii.

Changing environmental conditions or amputating worms do not alter the segment number threshold requirement for germline development.

The vasa‐expressing germ clusters are not required for regeneration in Platynereis dumerilii.

Genetic diversity and variation of seven Chinese grass shrimp (Palaemonetes sinensis) populations based on the mitochondrial COI gene

BACKGROUND

Chinese grass shrimp (Palaemonetes sinensis) is an important species widely distributed throughout China, which is ecologically relevant and possesses ornamental and economic value. These organisms have experienced a sharp decline in population due to overfishing. Therefore interest in P. sinensis aquaculture has risen in an effort to alleviate fishing pressure on wild populations. Therefore, we investigated the genetic diversity and variation of P. sinensis to verify the accuracy of previous research results, as well as to assess the risk of diversity decline in wild populations and provide data for artificial breeding.

METHODS

Palaemonetes sinensis specimens from seven locations were collected and their genetic variability was assessed based on mitochondrial COI gene segments. DNA sequence polymorphisms for each population were estimated using DNASP 6.12. The demographic history and genetic variation were evaluated using Arlequin 3.11. At last, the pairwise genetic distance (Ds) values and dendrograms were constructed with the MEGA 11 software package.

RESULTS

Our study obtained sequences from 325 individuals, and 41 haplotypes were identified among the populations. The haplotype diversity (H_d) and nucleotide diversity (π) indices ranged from 0.244 ± 0.083 to 0.790 ± 0.048 and from 0.0004 ± 0.0001 to 0.0028 ± 0.0006, respectively. Haplotype network analyses identified haplotype Hap_1 as a potential maternal ancestral haplotype for the studied populations. AMOVA results indicated that genetic variations mainly occurred within populations (73.07%). Moreover, according to the maximum variation among groups (F_CT), analysis of molecular variance using the optimal two-group scheme indicated that the maximum variation occurred among groups (53.36%). Neutrality and mismatch distribution tests suggested that P. sinensis underwent a recent population expansion. Consistent with the SAMOVA analysis and haplotype network analyses, the Ds and F_ST between the population pairs indicated that the JN population was distinctive from the others.

CONCLUSIONS

Our study conducted a comprehensive characterization of seven wild P. sinensis populations, and our findings elucidated highly significant differences within populations. The JN population was differentiated from the other six populations, as a result of long-term geographical separation. Overall, the present study provided a valuable basis for the management of genetic resources and a better understanding of the ecology and evolution of this species.

Effects of probiotics on digestive enzymes of fish (finfish and shellfish); status and prospects: a mini review

Digestive enzymes are found in the digestive tract of animals which assist in the breakdown of larger food molecules into more easily absorbed particles that can then be used by the body. The ability of fish to break down a diet is highly dependent on the availability of suitable digestive enzymes which mediate specific degradation pathways and on both the physical and chemical nature of food. Probiotics are known to produce helpful enzymes that aid in digestion and protect the gastrointestinal tract (GIT) of animals. When applied appropriately, probiotics improve intestinal microbial balance which also improves digestive enzyme activities, food absorption, and decrease pathogenic issues in the GIT. They work hand-in-hand with the digestive enzymes in the GIT of animals as supplements thereby improvings nutrition. This in turn leads to higher feed efficiency and growth as well as the prevention of antinutritional factors present in the ingredients, intestinal disorders, and pre-digestion. This review seeks to present summaries of the results of research findings on the application of probiotics on the activities of digestive enzymes including amylase, lipase, and protease. Further, this review points out gaps in available literature and suggests ideas that could be explored in further investigations to better understand and enhance the activities of these digestive enzymes to increase feed and nutrient utilization and the production of aquaculture species.

Genetic diversity and structure of Chinese grass shrimp, Palaemonetes sinensis, inferred from transcriptome-derived microsatellite markers

BACKGROUND

The Chinese grass shrimp, Palaemonetes sinensis, is an economically important freshwater shrimp in China, and the study of genetic diversity and structure can positively contribute to the exploration of germplasm resources and assist in the understanding of P. sinensis aquaculture. Microsatellite markers are widely used in research of genetic backgrounds since it is considered an important molecular marker for the analyses of genetic diversity and structure. Hence, the aim of this study was to evaluate the genetic diversity and structure of wild P. sinensis populations in China using the polymorphic microsatellite makers from the transcriptome.

RESULTS

Sixteen polymorphic microsatellite markers were developed for P. sinensis from transcriptome, and analyzed for differences in genetic diversity and structure in multiple wild P. sinensis populations in China. Totally of 319 individual shrimps from seven different populations were genotyped to find that allelic polymorphisms varied in two to thirteen alleles seen in the entire loci. Compared to other populations analyzed, the two populations including LD and SJ showed lower genetic diversity. Both the genetic distance (D) and Wrights fixation index (F_ST) comparing any two populations also indicated that LD and SJ populations differed from the other five populations. An UPGMA tree analysis showed three main clusters containing SJ, LD and other populations which were also confirmed using STRUCTURE analysis.

CONCLUSION

This is the first study where polymorphic microsatellite markers from the transcriptome were used to analyze genetic diversity and structures of different wild P. sinensis populations. All the polymorphic microsatellite makers are believed useful for evaluating the extent of the genetic diversity and population structure of P. sinensis. Compared to the other five populations, the LD and SJ populations exhibited lower genetic diversity, and the genetic structure was differed from the other five populations. Therefore, they needed to be protected against further declines in genetic diversity. The other five populations, LP, LA, LSL, LSY and LSH, are all belonging to Liaohe River Drainage with a relatively high genetic diversity, and hence can be considered as hot spots for in-situ conservation of P. sinensis as well as sources of desirable alleles for breeding values.

Evaluation of the effects of different stocking densities on growth and stress responses of juvenile hybrid grouper ♀ Epinephelus fuscoguttatus × ♂ Epinephelus lanceolatus in recirculating aquaculture systems

This study was aimed at evaluating the physiological and metabolic responses of juvenile hybrid grouper ♀ Epinephelus fuscoguttatus × ♂ Epinephelus lanceolatus to stocking density. Hybrid grouper juveniles (mean ± SE = 25.43 ± 2.36 g live mass) were stocked for 22 weeks in a recirculating aquaculture system (RAS) under four different densities: low stocking density (LD; 1.03 kg m^-3 ), medium stocking density (MD; 2.06 kg m^-3 ), high stocking density (HD; 3.09 kg m^-3 ) and extra-high stocking density (EHD; 4.11 kg m^-3 ). Biometric variables were recorded and plasma, liver, intestine and stomach samples were taken for biochemical analysis at the end of the experimental period. Final stocking densities were 6.27, 16.04, 23.77 and 28.32 kg m^-3 , respectively, with significant differences in growth performance. Our results showed that the best growth rates and feed utilisation occurred in the MD group. Higher plasma cortisol and glucose levels and lower triglyceride levels reflected the stress responses in the EHD group. Moreover, the activity of aspartate and alanine transaminases was elevated in the HD and EHD groups due to enhanced gluconeogenesis. The activity of the digestive enzyme pepsin significantly increased in the MD group. We found that 2.06-3.09 kg m^-3 is the most suitable starting density for culturing juvenile hybrid grouper in recirculating aquaculture systems.

Respiratory Metabolism Responses of Chinese Mitten Crab, Eriocheir sinensis and Chinese Grass Shrimp, Palaemonetes sinensis, Subjected to Environmental Hypoxia Stress

Environmental hypoxia represents a major physiological challenge for Eriocheir sinensis and Palaemonetes sinensis and is a severe problem in aquaculture. Therefore, understanding the metabolic response mechanisms of E. sinensis and P. sinensis, which are economically important species, to environmental hypoxia and reoxygenation is essential. However, little is known about the intrinsic mechanisms by which E. sinensis and P. sinensis cope with environmental hypoxia at the metabolic level. Hypoxia-reoxygenation represents an important physiological challenge for their culture. In this study, respiratory metabolism and respiratory metabolic enzymes of E. sinensis and P. sinensis were evaluated after different hypoxia and reoxygenation times. The results showed that environmental hypoxia had a dramatic influence on the respiratory metabolism and activities of related enzymes. The oxygen consumption rates (OCR) significantly increased as hypoxia time increased, while the ammonia excretion rate (AER) was significantly lower than that in the control group after 8 h hypoxia. The oxygen to nitrogen ratio (O:N) in the control group was <16, indicating that all the energy substrates were proteins. After environmental hypoxia, the O:N significantly increased, and the energy substrate shifted from protein to a protein-lipid mixture. The OCR, AER, and O:N did not restore to initial levels after 2 h or 12 h reoxygenation and was still the same as after 8 h hypoxia. As environmental hypoxia time increased, succinate dehydrogenase (SDH) gradually decreased and lactate dehydrogenase (LDH) gradually increased. Both SDH and LDH were gradually restored to normal levels after reoxygenation. Therefore, environmental hypoxia should be avoided as much as possible during aquaculture breeding of E. sinensis and P. sinensis. Further, since OCR will significantly increase after a short period of reoxygenation, secondary environmental hypoxia due to rapid consumption of oxygen should also be avoided in aquaculture.

Comparative transcriptome analysis of Chinese grass shrimp (Palaemonetes sinensis) infected with isopod parasite Tachaea chinensis

Parasitic isopods negatively affect reproduction and ingestion in several commercially important crustaceans; however, little is known about such parasite-host interactions. Therefore, we performed high-throughput sequencing of cDNA samples from Chinese grass shrimp Palaemonetes sinensis infected by parasitic isopod Tachaea chinensis and a non-infected control. We randomly assembled 46,858,882 and 41,110,746 clean reads from the parasitized and control groups, respectively. From these, we identified 1323 differentially expressed genes (DEGs) (p < 0.05), of which 702 were up-regulated and 621 were down-regulated after T. chinensis infection, respectively. The up-regulated genes were enriched in 'ribosome', 'purine metabolism', and 'pyrimidine metabolism' signalling pathways, suggesting altered host nucleotide metabolite levels, possibly through the action of intracellular parasites transported by T. chinensis. Additionally, 14 representative DEGs involved in reproduction were down-regulated after parasitisation, indicating T. chinensis causes cascading effects in P. sinensis. Overall, parasitisation appeared to affect host immune response, metabolism, and gonadal development. In conclusion, the present study improves our understanding on the molecular mechanisms underlying interactions between isopod parasites and their crustacean hosts.