Effects of dietary supplementation of Pseudomonas aeruginosa FARP72 on the immunomodulation and resistance to Edwardsiella tarda in Pangasius pangasius

Evaluation of Probiotic Efficacy of Bacillus subtilis RODK28110C3 Against Pathogenic Aeromonas hydrophila and Edwardsiella tarda Using In Vitro Studies and In Vivo Gnotobiotic Zebrafish Gut Model System

The indiscriminate use of antibiotics in aquaculture has led to the emergence of resistance; hence, eco-friendly, host-specific alternatives to mitigate bacterial infections have become imminent. In this study, bacteria that could possibly serve as probiotics were isolated and evaluated for their efficacy with in vitro experiments and in vivo zebrafish gut model. One isolate from each of the 23 rohu fish (Labeo rohita) was shortlisted after preliminary screening of several isolates and tested for their ability to inhibit two important warm water bacterial fish pathogens, Aeromonas hydrophila, and Edwardsiella tarda. An isolate (RODK28110C3) that showed broad-spectrum inhibitory activity against a battery of different isolates of the two fish pathogens included in this study and maintained in our repository was selected for further characterization. The culture was identified phenotypically as Bacillus subtilis and confirmed by 16S rDNA sequencing. The isolate was able to hydrolyze fish feed constituents that include starch, protein, and cellulose. Further in vitro tests ensured that the potential isolate with probiotic attributes could tolerate different gut conditions, which included a range of pH, salinity, and varying concentrations of bile salt. Exposure of 4 days post fertilization zebrafish embryos to the RFP-tagged isolate confirmed the colonization of B. subtilis in the gut of the zebrafish embryo, which is an important attribute of a probiotic. The isolate was able to inhibit both A. hydrophila and E. tarda in gnotobiotic zebrafish embryo in triplicate. The study demonstrates the probiotic characteristics of the B. subtilis isolated from L. rohita and its ability to inhibit A. hydrophila and E. tarda using in vitro conditions and in the zebrafish gut and could serve as an effective alternative to antibiotics in aquaculture.

Optimizing reproductive performance in pangasius catfish broodstock: A review of dietary and molecular strategies

Pangasius catfish, a significant player in the global whitefish market, encounters challenges in aquaculture production sustainability. Quality broodstock maintenance and seed production are impeded by growth, maturation, and fecundity issues. This review investigates the efficacy of strategic nutrient composition and molecular strategies in enhancing broodstock conditions and reproductive performance across various fish species. A notable knowledge gap for Pangasius catfish hampers aquaculture progress. The review assesses nutrient manipulation's impact on reproductive physiology, emphasizing pangasius broodstock. A systematic review analysis following PRISMA guidelines was conducted to identify research trends and hotspots quantitatively, revealing a focus on P. bocourti and fertilization techniques. Addressing this gap, the review offers insights into dietary nutrients manipulation and genetic tool utilization for improved seed production, contributing to pangasius catfish aquaculture sustainability.

Photoperiod manipulation improves growth performance, haematological indices and economic returns of Indian butter catfish, Ompok bimaculatus (Bloch, 1794)

Photoperiod manipulation is emerging as an effective approach for regulating physiological functions in fish. This study aimed to assess the impact of photoperiod on the growth performance, haematological responses, and economic returns of the endangered and highly valued Indian butter catfish, Ompok bimaculatus. Fish with an average body weight of 28.60 ± 4.78 g were randomly placed in six FRP tanks, each measuring 120 × 45 × 60 cm3. Each tank contained 20 fish exposed to a light intensity of 1500 lx under different photoperiods [24:0 light: dark (L: D), 15 L: 9D, 12 L: 12D, 9 L: 15D, 0 L: 24D and a natural photoperiod (control)], and fed at a daily rate of 2% of their body weight twice daily for 60 days. The fish in the 15 L: 9D photoperiod exhibited the highest final weight (g), percentage weight gain, specific growth rate (SGR) and survival rate, while the lowest was displayed in 24 L: 0D photoperiod group. The feed conversion ratio (FCR) was at its lowest in the catfish subjected to the 15 L: 9D photoperiod. Regarding haematological parameters, the 15 L: 9D photoperiod group showed higher total erythrocyte count, total leukocyte count, haemoglobin levels, and haematocrit values compared to the other groups. Conversely, the 0 L: 24D group, which experienced prolonged darkness, exhibited the lowest values in these parameters. Moreover, the 24 L: 0D, 9 L: 15D, and 0 L: 24D groups displayed a lower mean corpuscular volume (MCV) but higher mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) when compared to the control group. The economic analysis revealed that O. bimaculatus reared in a moderate photoperiod (15 L: 9D) displayed better growth, feed utilization, and overall health. This finding suggests that adopting a 15 L: 9D photoperiod can lead to enhanced production and improved economic returns for farmers culturing this high-value catfish in the future.

Effect of photoperiod on serum biochemistry, electrolytic balance, acute phase response and histopathology of butter catfish, Ompok bimaculatus (Bloch, 1794)

The present study was executed to evaluate the effect of photoperiod on serum biochemical parameters (glucose, cortisol, ALT, AST and LDH), electrolytic balance (Sodium and potassium), acute phase response (CRP) and histopathology (liver, kidney and skin) of an endangered high valued catfish, Ompok bimaculatus. Catfish (21.00 ± 1.53 cm and 30.00 ± 2.31 g) from the acclimatized stock were randomly distributed to six 120 × 45 × 60 cm3 FRP tanks (n = 20 fish per tank) and exposed to 1500 lx light intensity under different photoperiods [24:0 light: dark (L: D), 15L: 9D, 12L: 12D, 9L: 15D, 0L: 24D and a natural photoperiod (control)], and fed at a daily rate of 2% of bodyweight, twice a day for 60 days. Serum glucose, cortisol and enzymes including aspartate transaminase (AST), lactate dehydrogenase (LDH), alanine transaminase (ALT), and acute phase reactant, such as C-reactive protein (CRP) increased significantly (P < 0.05) in continuous light (24L: 0D), continuous dark (0L: 24D) and short day (9L: 15D) photoperiods, whereas in 15L: 9D and 12L:12D photoperiods, those were in decreasing trend. Serum electrolytes, i.e. potassium level was elevated and sodium level was declined in 24L: 0D, 0L: 24D and 9L: 15D photoperiod groups. Moreover, significant histological alterations in the liver, kidney and skin tissue were also evidenced in the experimented catfish. Typical polygonal hepatocytes with normal blood vessels in liver and normal organization of kidney were seen in catfish of 15L: 9D group. Histological analysis of other groups displayed nuclear degeneration, karyorrhexis, karyolysis, melanomacrophages, nuclear hypertrophy, sinusoid dilation and vacuolar degeneration in liver and hyaline droplets accumulation, granular degeneration, fragmentation of glomerulus and focal necrosis of epithelial cells in kidney. Additionally, general structure of the skin was observed in control group as well as in 15L: 9D group. Contrarily, in 24L: 0D group increased number of mucous cells and vacuoles was observed in the skin of butter catfish. In 9L: 15D and 0L: 24D photoperiods, O. bimaculatus exhibited ruptured epithelial cells, enlarged alarm cells, fat cells, necrotic cells and vacuoles in the skin tissue. The present study depicted that 15L: 9D photoperiod can induce better health of catfish, O. bimaculatus, which, in turn, can help farmers to increase the production of this high valued catfish in future.

Antibacterial Activity of Rainbow Trout Plasma: In Vitro Assays and Proteomic Analysis

The objective of this study was to investigate the bactericidal activity of blood plasma from cultured rainbow trout obtained from two different fish farms. Plasma from trout naturally infected with the bacterial pathogen Flavobacterium psychrophilum was found to inhibit the growth of Aeromonas hydrophila in vitro. Incubation of A. hydrophila in bacteriostatic trout plasma resulted in agglutination and growth retardation, without causing massive damage to the cell membrane. The proteome of the plasma with high antimicrobial activity revealed an abundance of high-density apolipoproteins, some isoforms of immunoglobulins, complement components C1q and C4, coagulation factors, lectins, periostin, and hemoglobin. Analysis of trout proteins retained on A. hydrophila cells revealed the presence of fish immunoglobulins, lectins, and complement components on bacteria whose growth was inhibited, although the native membrane attack complex of immunised trout plasma did not assemble effectively, resulting in a weak bactericidal effect. Furthermore, this study examined the bacterial response to trout plasma and suggested that the protein synthesis pathway was the target of antimicrobial proteins from fish blood. Taken together, these findings illustrate the advantages of the affinity approach for understanding the role of plasma proteins in host defence against pathogens.