Abstract
Fish protein hydrolysate (FPH) is the enzymatic hydrolysis of protein into smaller peptide and free amino acids, which has recently captured considerable attention as a supplementary ingredient in the aqua-feed industry sector. The present research aimed to observe the physiological, biochemical, and bacteriological study of FPH-treated diets and its effects on growth, hematology, plasma biochemistry, liver and gut histopathology, and resistance to Aeromonas hydrophila infection in Pabda (Ompok pabda). Four experimental diets (35% crude protein) were formulated with graded FPH supplementation (0, 0.5, 1, and 2%). The feed physiological parameters such as expansion ratio, bulk density, water stability, and floatability were not significantly affected by dietary FPH levels (p > 0.05), except for the pellet durability index (PDI). Furthermore, the diets with 1% and 2% FPH were more palatable to fish than other treatment diets. The total bacteria (TB) in fish diets and guts followed an increasing trend with the increase in various levels of FPH in diets. The significantly highest body weight, specific growth rate (SGR), total biomass (TB), survival rate (SR), condition factor (CF), and hepatosomatic index (HSI) were noted in 2% FPH-fed fish when compared with other treatment groups (p < 0.05). The feed intake of fish was significantly increased when increasing the FPH in diets (p < 0.05). The fish fed with a 2% FPH diet had significantly higher neutrophil, monocyte, lymphocyte, red blood cell, and platelet levels (p < 0.05). The blood glucose, creatinine, total protein, and globulin were significantly lower in control fish compared to other treatment groups (p < 0.05). The histopathological observation of mid intestine tissues displayed that 2% of FPH-diet-fed fish had a well-anchored epithelial wall with well-arranged goblet cells, a long villus structure, stratum compactum, and tunica muscularis compared to other treatments of FPH. The inclusion of FPH in diets up to 2% significantly improved the liver health of fish. The fish fed with 2% FPH had a significantly lower cumulative percent mortality (16.67%) against A. hydrophila infection in the bacterial challenge test (p < 0.05). Therefore, the present results suggested that using 2% FPH in the aqua-feed industry improves the growth performance, health status, and disease resistance of Pabda fingerlings in captivity.