Multi-strain Native Probiotics from the Asian Stinging Catfish (Heteropneustes fossilis) Enhance Growth, Blood Health, and Organ Morphology in the Host.

Probiotics are promising substitute to synthetic agrochemicals for improving fish health in the aquaculture system. The probiotics used in the aquaculture sector of Bangladesh are mostly imported. While these probiotics can offer benefits, probiotic-supplemented diet sometimes shows inconsistent results mainly due to incompatibility between the probiotic strains and local aquatic environment or fish species. Therefore, the development of probiotics from native fish species could be an alternative to mitigate the possible detrimental effects of imported probiotics on aquaculture production in Bangladesh. Thus, this study aimed to isolate and identify potential probiotic bacteria from the gut of Asian stinging catfish and to evaluate their efficiency in improving physiological parameters and organ morphology of the host fish. Following morphological and biochemical screening of the bacterial isolates, five isolates having potential probiotic traits were identified as Bacillus safensis (HF8), Bacillus altitudinis (HF10), Bacillus pacificus (HF19), Bacillus cereus (HF20), and Bacillus cereus (HF21) using 16S rRNA sequencing through the Barcode-Tagged Sequencing™ (BTSeq™) platform. Five probiotic bacteria, either individually or as a consortium, showed varying degrees of susceptibility to the thirteen antibiotics tested. Isolates HF8, HF19, and HF21 and the probiotic consortium demonstrated antagonistic activity against Aeromonas hydrophila, with strain HF8 exhibiting better inhibition efficiency. Application of a consortium of probiotic bacterial strains (1.15 × 10 to 2 × 1.15 × 10 CFU/kg feed) through feed supplementation significantly improved the growth of the Asian stinging catfish compared to the untreated control after 60 days of the feeding trial. Similarly, probiotic-fortified diet significantly enhanced the hepatosomatic index and relative intestine weight in the studied fish. The hematobiochemical parameters showed varying responses to the probiotic-supplemented diets. Moreover, the probiotic consortium had positive effects on the morphological parameters of the intestine and liver compared to the control. Principal component analysis (PCA) and Pearson's correlation of the histomorphology indices demonstrated a positive impact of the laboratory-based probiotic-fortified diet on the intestine of the host fish. The gonadosomatic index and developmental stages of the ovary were also improved in the fish treated with probiotic consortium compared to the group fed with normal feed. Multi-location field-level trials should be done before applying this probiotic-fortified diet at the farmers' level, which could substantially improve the commercial fish production in an ecofriendly manner.