Effects of dietary Spirulina platensis on growth performance, body composition, haematology, immune response, and gut microflora of stinging catfish Heteropneustes fossilis

The study was conducted to determine the inclusion effect of Spirulina platensis as a feed supplement on growth performance, feed efficiency, body composition, haematology, immune response, and gut microflora of the stinging catfish (Heteropneustes fossilis). Five iso-nitrogenous and iso-lipidic diets were prepared by replacing fish meal (FM) with S. platensis at a rate of 0, 2.5, 5, 7.5, and 10% and referred to as control, SP2.5, SP5, SP7.5, and SP10 diets, respectively. Three replicate groups of fish (average weight of 0.75 g) were reared in glass aquaria (180 L water capacity) and fed with each of the experimental diets up to satiation level twice a day, 7 days a week for 70 days. At termination, growth performance, carcass composition, immune parameters, and gut microflora were assessed. Moreover, ten fish from each aquarium were challenged with Aeromonas hydrophila and cumulative mortality was recorded for 15 days. Significantly (P < 0.05) higher weight gain, specific growth rate (SGR, % day−1), lower feed conversion ratio (FCR), and higher protein efficiency ratio (PER) were recorded in fish fed with SP7.5 and SP10 diets compared to control. Dietary S. platensis inclusion at 7.5–10% levels significantly (P < 0.05) boosted the whole-body protein and ash contents of stinging catfish, while decreasing the lipid and moisture contents compared to the control. Haematological parameters significantly (P < 0.05) improved in the S. platensis supplemented diet compared to the control. Serum lysozyme activity of fish fed with SP7.5 and SP10 diet was significantly (P < 0.05) higher compared to all other diets. Higher inclusion of S. platensis lowered post-challenge mortality and the lowest cumulative mortality (30%) was recorded in fish fed with the SP7.5 diet compared to the control (70%). Pseudomonas, Lactobacillus, and Lentibacillus were the prevalent genera in the gut microbiota found in the metagenomics study and the abundances of the above microbiota gradually increased with the level of dietary S. platensis inclusion. Based on the findings of the study, 7.5–10% inclusion of S. platensis was the most recommendable in stinging catfish diet to improve growth performance, feed utilization, body composition, haematology, immunological response, and gut microbiology. However, based on the regression analysis the optimum inclusion level of S. platensis as a feed supplement was calculated to be 9.3–9.9% in stinging catfish.