Sofia Priyadarsani Das

Probiotics have gained wide popularity as environmentally sustainable replacement for antibiotics in aquaculture due to their ability to up-regulate the host immune competence and boost disease resistance. However, considerable knowledge is yet to gain regarding differential efficacies and mechanisms of actions of Single-strain vs multi-strain probiotics. In the present review, the differences between the immunomodulatory potentials of Single-strain and multi-strain probiotics in fish and shellfish were thoroughly compared, with focus on immune gene expression of immunity markers and alteration of gut microflora. Single-strain probiotics usually mount a targeted immune response by enhancing the expression of particular immunity parameters, whereas multi-strain probiotics generally interact synergistic to induce more general and enhanced immune response and greater microbial diversity in the gut. Molecular basis and mechanisms underpinning probiotic mediated immunomodulation were also comprehensively documented in this review. Although recent evidence demonstrate that multi-strain probiotics tend to offer a broader and consistent immune defence against pathogens than Single-strain formulations, the efficacy of probiotic supplements is often context-specific, depending on the rearing environmental condition, dosage, strains compatibility etc. The combination of probiotics and biofloc system has been proposed as a promising and eco-friendly technology for the development of the sustainable aquaculture and animal welfare. Finally, existing research gaps and future directions have also been discussed for sustainable aquaculture.

Anabas testudineus, a significant nutritious food fish species, is experiencing substantial population decline due to several anthropogenic activities and urbanisation. Thus, population genetic structure of 156 A. testudineus samples from seven different geographical region of India was analysed using mitochondrial D-loop marker. We identified 22 haplotypes across these populations, with haplotype 5 and 8 commonly shared among populations. The overall haplotype and nucleotide diversity was found to be 0.879 and 0.074 indicating the presence of significant genetic diversity. AMOVA analysis revealed that within-population variance accounted for 3.53% of genetic variation, whereas among-population variation accounted for 96.47%. Pairwise FST ranged from 0.15581 to 0.99875. Significant genetic differentiation was observed among all populations except between the UP and MN population. Furthermore, the FST was observed to be 0.965, signifying the presence of notable genetic diversity. These findings are important for efficient conservation programs thereby preserving species' genetic diversity and productivity.

The gastrointestinal microbiota is crucial for the health and physiology of aquatic organisms, influencing their nutrition, metabolism, and immune responses. This review compares the diversity and function of gut microbial communities in finfish and shellfish, highlighting differences between freshwater and marine species as well as variations within shellfish taxa. We examine how these microbes aid in digesting complex dietary substrates, assimilating nutrients, and synthesizing essential metabolites, all of which are vital for host health. The structure of these microbial communities is shaped by a complex interplay of environmental factors, such as water temperature, salinity, and pH, and host-specific factors, including genetics and diet. A comprehensive understanding of these interactions is key to improving gut health and nutrient use in aquaculture. This review also identifies future research directions, focusing on the use of probiotics, prebiotics, and dietary interventions. These strategies, combined with multi-omics approaches, have great potential to enhance the sustainability of aquaculture by improving growth performance, feed conversion efficiency, and disease resistance in farmed aquatic species.

Extracellular vesicles (EVs) are functional substances secreted by microbes and host cells, and it has been discovered that they participate in the interactions between different microorganisms. Our recent findings indicate that Limosilactobacillus reuteri-derived EVs have the potential to improve the intestinal microbiota of Oplegnathus fasciatus fish and inhibit pathogenic bacteria. Previous research has reported that the host intestinal cells play a regulatory role in the intestinal microbiota. This suggested that to investigate the mechanisms through which L. reuteri-derived EVs regulate the intestinal microbiota, a system that excludes interference from host intestinal cells should be established. In this study, an in vitro cultured intestinal bacteria system, without host factors, was used to simulate the intestinal microbiota of O. fasciatus fish. After adding L. reuteri-derived EVs to the system, the changes in the microbiota were analyzed. The results showed that L. reuteri-derived EVs effectively reduced the abundance of Vibrio spp. In the results of the in vitro experiments, it was also observed that L. reuteri-derived EVs have the ability to inhibit Vibrio alginolyticus. We further sequenced the small RNA contained in L. reuteri-derived EVs and found that these small RNAs can interfere with genes (LysR, pirin, MIpA/OmpV, CatB, and aspartate-semialdehyde dehydrogenase) related to the growth of V. alginolyticus. Taken together, the results indicate that in the absence of host involvement, the small RNAs present in L. reuteri-derived EVs have the function of inhibiting pathogenic bacteria and exhibit the potential to regulate the intestinal microbiota.

Cirrhinus mrigala (mrigal) is one of the Indian major carps widely cultured in the whole Indian subcontinent. Population genetic structure of this species from Peninsular Rivers of India is lacking. Among DNA markers, microsatellites are excellent tools to evaluate genetic variation of populations. In this study, genetic variation of six peninsular riverine mrigal populations was evaluated using seventeen microsatellite loci. In analyzing 288 samples, the number of alleles ranged from 4 to 27; observed heterozygosity from 0.595 to 1.00, expected heterozygosity from 0.586 to 0.959 and inbreeding coefficient (FIS) ranged from -0.034 to 0.02. Exact test for Hardy Weinberg disequilibrium revealed that one locus was not in equilibrium across the rivers except one. The AMOVA analysis revealed the main source of genetic variation to be within the population (94.54%) than among the populations (5.46%). The Nei’s genetic distance and structure analysis depict river Narmada and Mahi populations are different from the four east coast rivers. The overall Fst (0.05462) data showed moderate differentiation among the six populations. The results of this study provide essential information to resource recovery and help in delineating populations for fishery management. Besides, the data will provide a valuable baseline for further investigations on the geographic distribution of this commercially important fish species.

The walking catfish Clarias magur (Hamilton, 1822) (magur) is an important catfish species inhabiting the Indian subcontinent. It is considered as a highly nutritious food fish and has the capability to walk to some distance, and survive a considerable period without water. Assembly, scaffolding and several rounds of iterations resulted in 3,484 scaffolds covering ∼94% of estimated genome with 9.88 Mb largest scaffold, and N50 1.31 Mb. The genome possessed 23,748 predicted protein encoding genes with annotation of 19,279 orthologous genes. A total of 166 orthologous groups represented by 222 genes were found to be unique for this species. The Computational Analysis of gene Family Evolution (CAFE) analysis revealed expansion of 207 gene families and 100 gene families have rapidly evolved. Genes specific to important environmental and terrestrial adaptation, viz. urea cycle, vision, locomotion, olfactory and vomeronasal receptors, immune system, anti-microbial properties, mucus, thermoregulation, osmoregulation, air-breathing, detoxification, etc. were identified and critically analysed. The analysis clearly indicated that C. magur genome possessed several unique and duplicate genes similar to that of terrestrial or amphibians’ counterparts in comparison to other teleostean species. The genome information will be useful in conservation genetics, not only for this species but will also be very helpful in such studies in other catfishes.