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Abstract Acute hepatopancreatic necrosis disease (AHPND) is an emerging disease in shrimp aquaculture which directly caused by binary photorhabdus insect-related (Pir) toxins PirABvp from Vibrio parahaemolyticus. To delineating the evolutionary origin and structure variation of PirAB, the protein sequence of PirABvp resembles from bacteria and insects were retrieved from the public database. The evolutionary relationship of PirABvp and resembles were analyzed phylogenetically. I-TASSER server was used to predict the protein-structure of PirA/B in investigated species. The cell-free supernatant obtained from the broth of V. parahaemolyticus and crude and heterologously expressed PirABvp proteins were respectively administrated to shrimp (Litopenaeus vannamei), crab (Eriocheir sinensis), European seabass (Dicentrarchus labrax), bloodworm (Nereis succinea) and mosquito (Aedes albopictus) to confirm the host range of toxin. Results showed that majority of PirAB located in a genomic island with low GC content. Phylogenetic analysis of PirB from bacteria and insects divided them into three lineages, namely Marine, Soli and Insect lineage respectively, with the majority belonging to Soli lineage. Overall, resembles of PirABvp were structurally similar to the PirABvp, but harbored three highly variable regions in receptor binding region and ligand binding sites, respectively. Shrimps bioassayed with cell-free supernatant of V. parahaemolyticus , crude and heterologously expressed PirABvp proteins resulted in 76.5%, 68.7% and 86.6% mortality, respectively. However, almost no mortality was found in crab, bloodworm, mosquito and European seabass. In summary, results indicated that PirBvp and its homologs have significant sequence divergence and remarkable variability in the receptor binding sites, which might explain why PirABvp are shrimp-specific toxins. Homology analysis of proteins revealed that there were three evolutionary directions for PirAB and the emergence of PirABvp was an ancient event that not associated with the aquaculture practices of shrimp. This study enhanced our understanding of the evolution of pirAB , which provided new insights into the origins of AHPND. However, why only shrimp is highly susceptible to PirABvp remains mysteries and need to solve in the future research. Highlights • The emergence of PirABvp was an ancient event that not associated with the aquaculture practices of shrimp. • PirB has species-specific receptor binding sites, which might affect its pathogenicity against the different host. • PirABvp has no adverse effects on other three animals and seems to be shrimp-specific toxins. [ABSTRACT FROM AUTHOR]

The outbreak of infectious bacterial diseases in aquaculture is a major concern in the industry. Among those pathogens, Aeromonas species are one of the most important bacterial pathogens of cultured animals. From May to June of 2022, an unexplained Aeromonas veronii outbreak was observed in a shrimp farm with high morbidity and mortality. To develop a risk assessment tool, the dynamics of the microbiome were monitored via absolute quantification of 16S rRNA amplicon sequencing for 18 consecutive days in a recirculating aquaculture system (RAS) for rearing water and the gut of whiteleg shrimp (Litopenaeus vannamei). A growth model was also developed for predicting the growth of Aeromonas in the shrimp gut and rearing water. The results showed that A. veronii is a dominant bacterial strain isolated from sick L. vannamei. The comparison of the bacterial community in the shrimp gut and rearing water over time showed remarkable shifts in A. veronii and probiotic Bacillus in the rearing water, with a significant decline in probiotic Bacillus. The rapid increase in A. veronii in rearing water subsequently altered A. veronii populations in the shrimp gut, with over 80% of A. veronii found on day 18. Linear regression analysis revealed a strong positive relationship between the abundance of A. veronii in the shrimp gut and the rearing water. The growth kinetic model agreed well with the observed values. Collectively, the temporal dynamics of the bacterial community in the rearing water offer valuable information for the fate of administered probiotics and pathogens. Growth kinetic models provide useful information to reduce the abundance of pathogens, which can be used as an early warning tool. These observations offer crucial insights into the dynamics of the bacterial community in shrimp and their environment, which can significantly impact shrimp health and productivity. • Absolute quantification of 16S rRNA amplicon sequencing was developed. • The dynamics of Aeromonas abundance in the shrimp gut and rearing water was record via this technology. • Predictive growth model of Aeromonas was established, which was in line with the results from observed data. [ABSTRACT FROM AUTHOR]

Abstract The present study reports on the effects of dietary glutathione (GSH) on non-specific immunity, oxidative stress resistance and detoxification in grass carp (Ctenopharyngodon idella) infected with microcystins. Six hundred and thirty juvenile grass carp with initial body weight of (5.10 ± 0.09) g were randomly distributed into six groups with three replicates each and stocked in 18 tanks (35 fish per tank), fed six diets containing graded levels of GSH for 60 days. At the end of the feeding trial, ten fish per tank were selected and injected intraperitoneally with 200 μg/kg body weight (BW) dose of pure microcystin-LR (MC-LR). The results showed that, at 0 h, 24 h of MC-LR injection, with the increase of dietary GSH content, serum lysozyme, alkaline phosphatase (ALP) and complement 3 (C3) levels, the activities and mRNA expression levels of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) in liver, and liver GSH content increased first and then decreased (P < 0.05). When dietary GSH content was 407.45 mg/kg diet, these parameters reached the highest levels (P < 0.05), and in the same dose of GSH group, in addition to lysozyme activity at 24 h was significantly higher than that at 0 h, the other indicators at 24 h were significantly lower than those before exposure (at 0 h) (P < 0.05). In contrast, serum cortisol and glucose, and liver reactive oxygen species (ROS) and malondialdehyde (MDA) contents decreased first and then increased (P < 0.05), when dietary GSH content was 407.45 mg/kg diet, the above parameters reached the lowest levels (P < 0.05), and in the same dose of GSH group their contents at 24 h were significantly higher than those before exposure (P < 0.05). In addition, before MC-LR exposure, the activities of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) had no significant difference of all groups (P > 0.05), liver glutathione S-transferase (GST) and its mRNA expression levels had a rising trend while liver glutathione reductase (GR) activities significantly decreased and then maintained a lower level with dietary GSH content increasing (P < 0.05). At 24 h of MC-LR injection, serum ALT and AST activities decreased at first and then increased while liver GST and GR activities and their mRNA expression levels increased first and then decreased (P < 0.05). Therefore, the basal diet supplemented with GSH 407.45 mg/kg could improve innate immunity, antioxidant stress ability and detoxification function of grass carp against MC-LR exposure. However, dietary excess GSH might promote oxidation, resulting in negative effect. Highlights • Dietary optimal GSH could improve innate immunity of grass carp injected with microcystins (MCs). • Dietary optimal GSH could improve antioxidant stress ability of fish. • Dietary optimal GSH could enhance detoxification function of fish against MCs. • Dietary excess GSH has negative effect on fish. [ABSTRACT FROM AUTHOR]

Selenium (Se) is an essential nutrient for crustaceans. The dietary selenium requirement of juvenile oriental river prawn Macrobrachium nipponense was evaluated. Yeast-selenium was added to basal semi-purified diet at six levels to make diets with the concentration of 0.11, 0.31, 0.47, 0.59, 0.88 and 1.17 mg Se kg − 1 . These diets were fed to juvenile prawns (initial weight 0.133 ± 0.003 g) in quintuplicate for 8 weeks. Our results indicated that the growth performance of prawn was significantly affected by dietary selenium. Prawns fed the 0.47 and 0.59 mg Se kg − 1 diets achieved the highest weight gain rate (WGR), whereas the deficiency (0.11 mg kg − 1 ) and excess (1.17 mg kg − 1 ) of Selenium inhibited their growth. Whole-body and muscle Se concentrations generally increased with the level of dietary Se. The highest concentrations in body and muscle were observed in the prawns fed the 1.17 mg kg − 1 diet, which were significantly higher than those of prawns using 0.11, 0.31, 0.47 and 0.59 mg kg − 1 diets. Selenium also affects the activity of antioxidant enzymes. The activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) were significantly higher in prawns fed with 0.31, 0.47 and 0.59 mg Se kg − 1 than other groups, whereas the maleic dialdehyde (MDA) content had the opposite pattern from GSH-Px activity. Significantly elevated glutathione reductase (GR) activity and reduced glutathione (GSH) content were found in prawns fed the 0.31, 0.47, 0.59 and 0.88 mg kg − 1 diets. The prawns fed with 0.31–0.88 mg Se kg − 1 exhibited the highest total antioxidant competence (T-AOC activity), which was significantly higher than 1.17 mg kg − 1 group. Furthermore, selenium is involved in prawn immune competence. Serum phenoloxidase (PO) and lysozyme activities in prawns fed the 0.31, 0.47, 0.59 and 0.88 mg Se kg − 1 diets were significantly higher than those fed the 0.11 and 1.17 mg Se kg − 1 diets. The minimum dietary selenium requirements for maximal growth and antioxidant ability of juvenile oriental river prawn were evaluated as 0.58–0.68 mg kg − 1 diet based on WGR and GSH-Px activity in the hepatopancreas, and 1.07 mg Se kg − 1 diet was required to maximize whole body selenium content. Statement of relevance In this study, we evaluated the minimum dietary selenium requirement for juvenile oriental river prawn Macrobrachium nipponense . Dietary selenium deficiency and excess significantly reduced growth, antioxidant ability and immunity of prawn. Our results illustrate that supplementing appropriate amount of dietary selenium is necessary in prawn culturing. The minimum dietary selenium level for maximal growth and antioxidant ability of juvenile M. nipponense is recommended as 0.58–0.68 mg kg − 1 diet based on the analyses of WGR and GSH-Px activity, and 1.07 mg Se kg − 1 diet is required to maximize whole body selenium content. This research will facilitate to the development of practical diet for prawn. [ABSTRACT FROM AUTHOR]

The present study evaluated the effect of different sources of dietary carbohydrate on the growth, immunity, antioxidant capacity, and digestive enzyme and carbohydrate metabolism enzyme activities in the juvenile oriental river prawn, Macrobrachium nipponense. The experimental diets, which comprised raw maize starch, pregelatinized maize starch, dextrin, maltose, glucose or cellulose, were fed to juvenile prawns for 56 days, respectively. We found that prawns fed with starch, dextrin or maltose achieved better growth. The highest digestive enzyme activities were noted in prawns fed with starch or dextrin. Furthermore, the prawns fed with starch, dextrin or maltose exhibited significantly higher levels of hepatopancreas hexokinase (HK) and phosphofructokinase (PFK) activities. Phosphoenolpyruvate carboxykinase (PEPCK) activity was higher in prawns fed with dextrin, maltose or cellulose, and higher glucose-6-phosphate dehydrogenase (G6PDH) activities were observed in prawns fed with starch or dextrin. We further evaluated the effect of different dietary carbohydrate sources on antioxidant capacity and immune competence. Prawns supplied with starch exhibited superior activities of superoxide dismutase (SOD), catalase (CAT), total antioxidant capacity (T-AOC), lysozyme and respiration burst, and had lower level of maleic dialdehyde (MDA). In summary, the dietary addition of starch is a promising option for juvenile prawn farming, given its positive effect on the growth, glycolysis, pentose phosphate pathway, antioxidant activity and immunity of prawns. • Prawns fed starch, dextrin or maltose achieved higher growth than those fed on glucose or cellulose. • Dietary starch induced the glycolysis and pentose phosphate pathways, and depressed the gluconeogenesis pathways of prawn. • Prawns fed on starch exhibited significantly higher digestive enzyme activities, antioxidant capacity and immunity. [ABSTRACT FROM AUTHOR]

Arachidonic acid (ARA) is involved in the growth and regulation of immunity in fish. Little research has focused on ARA in crustaceans. This study was an 8-week feeding experiment investigating the effects of dietary ARA on growth, antioxidative indices, and immune characteristics of the juvenile oriental river prawn ( Macrobrachium nipponense ). An ARA-enriched oil was supplemented into the basal diet to formulate six isonitrogenous and isoenergetic diets containing 0.02% (the control group), 0.28%, 0.54%, 0.86%, 1.22%, and 1.54% ARA dry weight. Diets were fed to juvenile prawns (mean weight: 0.104 ± 0.002 g) twice daily to apparent satiation in three replicates. Weight gain and specific growth rate of M . nipponense significantly increased with increasing dietary levels of ARA from 0.02% to 0.86% and thereafter declined. Hepatopancreas super oxide dismutase and catalase activities significantly increased with supplementation with ARA, particularly in prawns fed 1.22% and 1.54% ARA. The malondialdehyde level in prawns fed 1.54% ARA also significantly increased, and was higher than that of prawns fed ARA from 0.02% to 0.86%. Serum lysozyme activity was significantly greater in prawns fed 0.86% ARA compared with the other groups. mRNA expression of toll-like receptor signaling pathway-related genes was promoted by a dietary ARA level from 0.54% to 0.86% but inhibited with the higher ARA levels (1.22–1.54%). The mortality percentage increased after challenge with live Aeromonas hydrophila . The mortality percentage of prawns fed 1.54% ARA was significantly higher than that of prawns fed 0.28–1.22% ARA. The results suggest that the optimal dietary ARA requirement for juvenile M . nipponense is 0.82% (dry weight) based on second-order regression analysis of weight gain vs . dietary ARA level, and that 0.86% ARA could significantly enhance non-specific immunity of M . nipponense ; however, too high a level of ARA will affect the health status of this prawn. [ABSTRACT FROM AUTHOR]

The present study evaluated the effects of magnesium (Mg) on growth, antioxidant capacity, intestinal morphology and ammonia nitrogen resistance in juvenile oriental river prawn, Macrobrachium nipponense. Six semipurified diets (crude protein 401.1 g kg−1 diet; crude lipid 88.7 g kg−1 diet) containing Mg levels of 1.1, 1.4, 1.6, 2.1, 2.8 or 4.5 g kg−1 were formulated. A total of 1080 healthy juvenile prawns (0.151 ± 0.003 g) were randomly stocked into eighteen 300 L tanks (100 × 80 × 60 cm), each tank with 60 prawns. Each experimental diet was fed to prawns in triplicate twice daily (08:00 and 17:00) for eight weeks. After the feeding trial, 20 prawns from each tank were challenged with 37 mg/L ammonia nitrogen for 96 h, and the hemolymph, hepatopancreas and muscle of the rest of the prawns were collected. Final biomass was higher in prawns fed diets containing 1.6 and 2.1 g Mg kg−1 compared with those fed the diet with 1.1 g kg−1. Higher alkaline phosphatase (ALP) activity was obtained in the serum of prawns fed the 2.1 and 2.8 g Mg kg−1 diets. The highest activities of hepatopancreas superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and total antioxidant capacity (T-AOC) were observed in prawns fed 1.6–2.8 g Mg kg−1 of feed, and the lowest hepatopancreas malondialdehyde (MDA) concentrations and serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were found in these treatment groups. Similarly, the prawns fed diets with 1.6 and 2.1 g Mg kg−1 had significantly lower MDA concentrations and cumulative mortality and higher antioxidant enzyme activities after ammonia nitrogen exposure. The intestinal epithelial cells were closely attached to the membrane in prawns fed the 2.1 g Mg kg−1 diet, but they were partly detached in those fed the 1.1 and 4.5 g Mg kg−1 diets. The minimum dietary Mg supplementations of juvenile M. nipponense were determined to be 1.6, 1.9, 2.0 and 2.2 g kg−1 feed, respectively, using broken-line regression analysis based on the final biomass, SOD, ALT and ALP. • Optimal dietary magnesium (Mg) enhanced antioxidant capacity and health of juvenile Macrobrachium nipponense. • After ammonia stress, prawns fed on 1.6 and 2.1 g Mg kg−1 had lower cumulative mortality and higher antioxidant capacity. • Dietary supplementation of 1.6–2.2 g Mg kg−1 feed is recommended to promote the growth and well-being of juvenile prawns. [ABSTRACT FROM AUTHOR]

Manganese (Mn) is an essential micronutrient for animals. An 8-week feeding experiment with oriental river prawn Macrobrachium nipponense was conducted to determine the effects of Mn supplementation on growth, antioxidative indices, intestinal morphology, and gut microbiota in juveniles of this species. Manganese sulfate monohydrate was added to a basal semi-purified diet at six levels: 5.4 (control), 13, 22, 34, 73 and 150 mg Mn kg−1 diet. Each diet was fed to juvenile prawns (mean weight 0.104 ± 0.003 g), twice daily to apparent satiation, in four replicates. Prawns fed the 22 mg Mn kg−1 diet achieved the highest weight gain. The Mn concentration in muscle significantly increased with increased dietary Mn supplementation, from 5.4 to 22 mg kg−1 diet, but leveled off in animals fed greater levels. Prawns fed the 34 mg Mn kg−1 diet had the lowest malondialdehyde content. Total superoxide dismutase activity in the hepatopancreas increased significantly with an increasing level of dietary Mn in the groups fed the 5.4 (control) to 73 mg kg−1 diets, but plateaued with higher levels of supplementation. Prawns fed the 13–150 mg Mn kg−1 diets had significantly higher Mn superoxide dismutase activity than those fed the 5.4 mg kg−1 diet. Epithelial cells of the intestine were closely arranged, with clear cell definition, in the groups fed the 5.4 (control) or 22 mg Mn kg−1 diet, whereas these cells were completely separated from the basement membrane in prawns fed the 150 mg Mn kg−1 diet. The estimator of community richness (Chao1) in the intestine was significantly higher for prawns fed the 22 mg Mn kg−1 diet as compared with animals fed the 5.4 (control) and 150 mg Mn kg−1 diets. The dominant phyla in the gut of M. nipponense were Proteobacteria, followed by Firmicutes and Bacteroidetes, regardless of the level of Mn supplementation. The intestinal microbiota phylotypes significantly differed among the groups fed the 5.4 (control), 22 and 150 mg Mn kg−1 diets. We conclude that Mn supplementation in formulated feeds for this species can improve growth performance and Mn deposition in muscle, whereas diets causing Mn deficiency or excess will induce oxidant stress, and very high levels of dietary Mn could damage the intestinal morphology. The intestinal core microbiota were not affected by the dietary Mn level, although the microbiota richness was somewhat affected. Based on weight gain, the optimal level of Mn supplementation for juvenile M. nipponense is 17.59 mg kg−1 diet. • The optimal level of Mn supplementation for juvenile M. nipponense is 17.59 mg/kg diet. • Mn deficiency or excess could induce oxidative stress. • High dietary Mn may damage the intestinal morphology. • Dominant phyla in the gut are Proteobacteria, followed by Firmicutes and Bacteroidetes, regardless of the level of dietary Mn. • Microbial richness in the gut juveniles is somewhat affected by the level of Mn supplementation in the feed. [ABSTRACT FROM AUTHOR]