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To understand the host-gut microbial relationship, we used multidisciplinary platforms, metagenome, transcriptome, and metabolome analyses, to determine shrimp and intestinal microbial interactions upon 0, 6, 12, 24, and 48 h exposure to 107 CFU/mL of Vibrio harveyi, a shrimp pathogen. The bacterial communities in the intestine of shrimp were disrupted during exposure to V. harveyi. The abundance of Vibrio ASVs in the Harveyi and Vulnificus clades was significantly increased after exposure to the pathogen (6, 12, and 24 h) and decreased later after 48 h. Conversely, Pseudoalteromonas was found in lower abundance (6, 12, and 24 h) but significantly increased after 48 h of the bacterial challenge. Gene expression analysis revealed that genes belonging to several immune-related pathways, including the Toll pathway, the immune deficiency (IMD) pathway, and pattern recognition proteins (PRPs), were significantly upregulated. Early responses in the first 6 h after exposure were the genes involved in phagocytosis, pattern recognition proteins (PRPs), and signal transduction (spätzle and ankyrin). Late responses (12–48 h) were genes related to proteinases and proteinase inhibitors (PPIs), antimicrobial peptides (AMPs), and oxidative stress. Genes related to lipid metabolisms such as fatty acid metabolism and choline metabolism were also upregulated. Metabolomics analysis also showed an increase in phospholipids, including phosphocholine groups, in the intestine of shrimp exposed to the pathogen. Taken together, the gene expression and metabolomics analyses suggest the importance of lipid metabolism in the defense mechanism against bacterial invasion. Moreover, our metabolomic analysis showed a decrease in tryptophan and indole-3-acrylic acid, metabolites related to intestinal immune homeostasis, after bacterial infection. Our observations suggest that pathogenic Vibrio disrupted biological processes in the shrimp intestine, resulting in a decrease in indole-3-acrylic acid and its derivatives which in turn compromised intestinal immunity. In addition, shrimp responded to the bacterial invasion by activating metabolites related to eicosanoid and phospholipid biosynthesis. Our findings on the interactions between shrimp and intestinal microbiota will be an indispensable gateway to systems biology to better understand the function of shrimp gut microbiota and its influence on shrimp innate immunity.

The use of probiotics in aquaculture is a practical alternative to promote animal health and disease prevention. Meanwhile, this practice can also reduce the use of prophylactic antibiotics. The purpose of this study was to identify candidate probiotics that could control pathogen populations in host's gastrointestinal (GI) tract and stimulate host immunity in shrimp aquaculture. Bacillus aryabhattai TBRC8450, a bacterial strain isolated from the environment in a shrimp farm, has an antimicrobial activity against many pathogenic strains of Vibrio harveyi and V. parahaemolyticus. Supplementation of B. aryabhattai to Pacific white shrimp (Litopenaeus vannamei) not only decreased the abundance of Vibrio populations, but also shifted the bacterial community in the shrimp GI tract. We found that supplementation of B. aryabhattai triggered shrimp innate immunity and antioxidant activities. mRNA expression of genes encoding microbial peptides and antioxidant enzymes, including C-type lectin, penaeidin-3, heat shock protein 60, thioredoxin, and ferritin, was significantly upregulated in the hepatopancreas of shrimp fed B. aryabhattai. Furthermore, phenoloxidase activity in the hemocytes and the total antioxidant activity in the plasma were increased, indicating enhanced immune and antioxidant responses at the systemic level. In contrast, supplementation of B. aryabhattai had no effect on the total hemocyte count and superoxide dismutase activity in the plasma and hepatopancreas. Importantly, a pathogen challenge test using V. harveyi 1562 showed a significant increase in survival rates of shrimp fed B. aryabhattai compared to the control group. Our findings suggest that B. aryabhattai TBRC8450 can likely be used as a probiotic to reduce the population of V. harveyi in the shrimp GI tract and to enhance shrimp innate immunity and antioxidant capacity for vibriosis resistance in shrimp aquaculture.

Long-chain polyunsaturated fatty acids (LC-PUFAs) have been shown to promote growth and health of many larval marine animals. Producing high amounts of LC-PUFAs, thraustochytrids are potential alternatives to fish oil as feed supplement for marine larviculture. Their applications have been assessed in many larval aquatic species but not yet in larval and post-larval (PL) shrimp. Here, growth performance and health of Penaeus vannamei PL were evaluated when fed with a thraustochytrid, Aurantiochytrium limacinum BCC52274 (AL), via enrichment in instar-II Artemia. Instar-II Artemia was enriched with AL for 4 h at the ratio of 400,000 individuals: 600 mg of freeze-dried AL per 1l of 30-ppt water. The feeding experiment consisted of treatment groups fed with varied proportions (from 0 to 100%) of the number of meals offering the non-enriched and enriched instar-II Artemia. Additionally, a reference group was included, in which PL were fed only with instar-I Artemia, the stage commonly used in commercial practice. AL enrichment replenished DHA deficiency in Artemia and increased LC-PUFA content in the fed PL. Increased feeding amounts of the enriched Artemia yielded positive effects on increased biomass gain, longer average length and decreased length variation coefficient of the PL (P 0.05). These findings suggest benefits of AL on growth performance, increasing hypo-salinity tolerance and swimming strength of shrimp PL.

The recent trend for rainbow trout feeds to be higher than 15% lipid may improve feed conversion ratios (FCRs) and increase the lipid concentration of the fish. However, one disadvantage of the higher lipid concentration in fish is the potential for increased rates of lipid oxidation, which could affect fish health and contribute to off-flavors in fillets. The objective of this experiment was to determine the effects of adequate and high concentrations of dietary lipid and the antioxidant vitamin E on fish performance, fish health, and fillet product quality of rainbow trout. A 10-week feeding trial was conducted with diets containing either 15 or 30 g lipid/100 g feed, and either 300 (e) or 1500 (E) mg dl-α-tocopheryl acetate/kg feed (15e, 15E, 30e, and 30E). Fish fed 30% lipid diets had significantly higher final body weight, specific growth rate (SGR), and protein efficiency ratio (PER) than fish fed 15% lipid diets. All health parameters of fish measured in the experiment were within normal ranges of healthy fish although several parameters were affected by increasing dietary lipid concentration. Lipid concentration in fish body (whole body, fillets, and viscera) reflected dietary lipid concentration. Increasing the lipid concentration in the feed from 15% to 30% increased the fillet lipid concentration from 8.4 to 9.6 g lipid/100 g fillet. Vitamin E concentrations in fillets reflected dietary vitamin E concentration and ranged from 8.3 mg/kg (30e) to 49.1 mg/kg (15E) (P