Effects of autochthonous strains mixture on gut microbiota and metabolic profile in cobia (Rachycentron canadum)

Intestinal Tissue, Digestive Enzyme, and Antioxidant Enzyme Activities in the Early Development Stage of Endangered Brachymystax tsinlingensis

This work explores the digestive system characteristics of Brachymystax tsinlingensis during early developmental stages and aims to solve the problem of high lethality of fry during the transgression period, which is crucial for the artificial propagation and population conservation of endangered fishes. This study was carried out on intestinal tissue, digestive enzymes, and antioxidant enzyme activities in the early development stage of Brachymystax tsinlingensis. Ten random samples during endogenous nutrition (7, 10, and 11 days after hatching), mixed nutrition (13 and 19 DAH), and exogenous nutrition (31, 33, 39, 45, and 73 DAH) were collected by histological and biochemical analysis methods. The results showed that the intestine of Brachymystax tsinlingensis already has four layers initially at 7 DAH, and the intestinal gland tissue is evident at 73 DAH. The contents of total protein (TP) and the activities of lipase (LPS) and trypsin (TPS) were maximal at 39 DAH, and the activities were 3.20 ± 0.26 mg/mL, 2.52 ± 0.69 U/g, and 2717.45 ± 295.26 U/mg, respectively. Catalase (CAT) and glutathione peroxidase (GSH-PX) activities both showed the lowest values at 39 DAH, which were 0.57 ± 0.11 U/mg and 3.35 ± 0.94 U/mg, respectively. The activity of amylase (AMS) and the content of malonaldehyde (MDA) increased, and the highest values were reached at 45 DAH (1.32 ± 0.41 U/mg) and 73 DAH (1.29 ± 0.43 nmoL/mg), respectively. Superoxide dismutase (SOD) and GSH-PX activities both showed a peak value at 7 DAH (126.58 ± 20.13 U/mg and 6.47 ± 1.86 U/mg). Overall, the changes in intestinal tissue, digestive enzymes, and antioxidant enzyme activities at 39 DAH of Brachymystax tsinlingensis are inseparable from different vegetative stages during the developmental period, and these results can provide a reference for the proliferation and cultivation of Brachymystax tsinlingensis resources.

Association between Turbot (Scophthalmus maximus) Fish Phenotype and the Post-Larval Bacteriome

Over the past decade, an increasing number of studies have emphasized the importance of the host microbiome in influencing organismal health and development. Aligned with this understanding, our study aimed to investigate the potential association between the turbot (Scophthalmus maximus) phenotypic traits and the post-larval bacteriome. Turbot post-larvae were sampled from twenty randomly selected production cycles thirty days after hatching (DAH) across multiple post-larval production batches over a three-month period (April to June). Fish were selectively sampled based on five phenotypic traits, namely, normal, large, small, malformed, and depigmented. Our results showed that small-sized post-larvae had significantly higher bacterial phylogenetic diversity in their bacterial communities than all other phenotypes. A more in-depth compositional analysis also revealed specific associations between certain bacterial taxa and fish phenotypes. For example, the genera Aliivibrio and Sulfitobacter were enriched in small-sized post-larvae, while the family Micrococcaceae were predominantly found in larger post-larvae. Furthermore, genus Exiguobacterium was linked to depigmented larvae, and genus Pantoea was more prevalent in normal post-larvae. These observations underscore the importance of further research to understand the roles of these bacterial taxa in larval growth and phenotypic differentiation. Such insights could contribute to developing microbiome modulation strategies, which may enhance turbot post-larval health and quality and improve larviculture production.

Functional and mechanistic studies of a phytogenic formulation, Shrimp Best, in growth performance and vibriosis in whiteleg shrimp

Climate change and disease threaten shrimp farming. Here, we studied the beneficial properties of a phytogenic formulation, Shrimp Best (SB), in whiteleg shrimp. Functional studies showed that SB dose-dependently increased shrimp body weight and decreased feed conversion ratio. We found that SB protected against Vibrio parahaemolyticus as evidenced by survival rate, bacterial load, and hepatopancreatic pathology in shrimp. Finally, we explored the likely mechanism by which SB affects growth performance and vibriosis in shrimp. The 16S rRNA sequencing data showed that SB increased 6 probiotic genera and decreased 6 genera of pathogenic bacteria in shrimp. Among these, SB increased the proportion of Lactobacillus johnsonii and decreased that of V. parahaemolyticus in shrimp guts. To dissect the relationship among SB, Lactobacillus and Vibrio, we investigated the in vitro regulation of Lactobacillus and Vibrio by SB. SB at ≥ 0.25 μg/mL promoted L. johnsonii growth. Additionally, L. johnsonii and its supernatant could inhibit V. parahaemolyticus. Furthermore, SB could up-regulate five anti-Vibrio metabolites of L. johnsonii, which caused bacterial membrane destruction. In parallel, we identified 3 fatty acids as active compounds from SB. Overall, this work demonstrated that SB improved growth performance and vibriosis protection in shrimp via the regulation of gut microbiota.

Bacterial diseases in marine fish species: current trends and future prospects in disease management

The fisheries sub-sector of aquaculture-i.e., the pisciculture industry, contributes significantly to a country's economy, employing a sizable proportion of the population. It also makes important contributions to household food security because the current demand for animal protein cannot be fulfilled by harvesting wild fish from riverines, lakes, dams, and oceans. For good pond management techniques and sustaining fish health, the fisherfolk, and the industry require well-established regulatory structures, efficient disease management strategies, and other extended services. In rearing marine fish, infections resulting from disease outbreaks are a weighty concern because they can cause considerable economic loss due to morbidity and mortality. Consequently, to find effective solutions for the prevention and control of the major diseases limiting fish production in aquaculture, multidisciplinary studies on the traits of potential fish pathogens, the biology of the fish as hosts, and an adequate understanding of the global environmental factors are fundamental. This review highlights the various bacterial diseases and their causative pathogens prevalent in the pisciculture industry and the current solutions while emphasising marine fish species. Given that preexisting methods are known to have several disadvantages, other sustainable alternatives like antimicrobial peptides, synthetic peptides, probiotics, and medicinal treatments have emerged to be an enormous potential solution to these challenges.