Effect of fish meal substitution with trout viscera protein hydrolysate on the innate immune response of red tilapia (Oreochromis spp).

This study evaluated the effect of replacing fish meal (FM) with concentrated trout viscera protein hydrolysate (TVPH) on the immune response in juvenile red tilapia (Oreocheromis spp). Five isoenergetic and isoproteic experimental diets were prepared by substituting FM with TVPH at different substitution ratios: 0% (control, D1) 25% (D2), 50% (D3), 75% (D4), and 100% (D5). A total of 180 red tilapia were distributed in 15 tanks. Fish from three tanks were fed daily at 2% of the biomass for 25 days with one of the five diets mentioned above. At the end of the trial, the fish were counted, weighed, measured, and skin mucus and serum samples were obtained to study different parameters related to humoral immunity. The results indicate a 100% survival rate in all fish groups and did not show significant differences in terms of growth and feed efficiency. On the other hand, the fish fed diets D2 and D3 had significantly higher serum protein values. Also, fish fed the D2 or D5 diets had higher lysozyme activity and fish fed the D2 diet also had significantly higher total immunoglobulin levels than fish fed the control diet. In mucus, fish fed the D2 or D4 diets showed significantly higher mucus protein levels than control fish. However, anti-protease and bactericidal activity decreased in fish fed the D5 or D4 diets, respectively. These results demonstrate that the D2 and D3 diets positively modulate the immune response of juvenile red tilapia compared to that of fish fed the control diet.