Effect of fish meal substitution with dried bovine hemoglobin on the growth, blood hematology, antioxidant activity and related genes expression, and tissue histoarchitecture of Nile tilapia (Oreochromis niloticus)

Our study was designed to highlight the efficacy of fish meal (FM) replacement with dried bovine hemoglobin (DBH) on the Oreochromis niloticus (O. niloticus) growth, health antioxidant activity, and antioxidant-related gene expression for 70 days. Fish (n = 225, average weight: 36.37 +/- 0.05 g) were fed diets with different replacement percentage of FM with DBH: 0 % (DBH0), 2.5 % (DBH2.5), 5 % (DBH5), 7.5 % (DBH7.5) and 10 % (DBH10), where DBH0 was kept as control diet. At the end of the feeding trial, the fish were exposed to bacterial challenge with the pathogenic bacteria Aeromonas veronii (A. veronii). Compared to the DBH0 group, there was a notable increase in the growth parameters with a lower feed conversion ratio in all DBH groups, with DBH10 recording the highest growth. The DBH (0-5 %) diets did not alter the leukogram and erythrogram of O. niloticus, whist, the DBH (7.5-10 %) diets badly affected the leukogram and erythrogram of the fish. The DBH7.5 and DBH10 diets significantly increased (p < 0.05) the levels of hepato-renal function indicators. A significant increase (p < 0.05) in the hepatic antioxidant parameters and its related gene expression in the spleen with a lower level of malondialdehyde was detected in the DBH5 and DBH7.5 groups, followed by DBH10 then DBH2.5 compared to DBH0 group. Hepatic and renal tissue architecture showed normal histomorphological structure in DBH (0-10 %), except a mild interstitial lymphocytic infiltration and melano-macrophages proliferative activation could be observed in DBH7.5 to10 %. As a result, the DBH at a percentage up to 5 % could be used as a substitution for FM without affecting the fish growth, health, hematological parameters, the oxidant/antioxidant balance, and he-patic and renal tissue architecture, which serves the sustainable aquaculture industry.