The influences of ferulic acid on the growth performance, haemato-immunological responses, and immune-related genes of Nile tilapia (Oreochromis niloticus) exposed to heat stress

Abstract

The use of food additives is an important preventive approach that has proven to maintain the health status of fish, especially under stressful conditions. The dietary ferulic acid (FA) was included in the diets at 0, 20, 40, 80, and 160 mg per kg to investigate its beneficiary aspects on Nile tilapia. After 60 days, fish were exposed to heat stress (HS), then blood and liver samples were collected. Before HS, the growth performance was linearly and quadratically affected by the inclusion of FA and reported the highest rates by 80 mg/kg diet. The hemoglobin and red blood cells were also linearly and quadratically affected by dietary FA and reported the highest levels by 40 and 80 mg FA/kg. After HS, the blood glucose, cortisol, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and malondialdehyde (MDA) values were increased with comparison to the rates before HS, and dietary FA reduced theses values either before or after HS in a dose-dependent regime (linearly and quadratically P < .05). Before HS, SOD was increased by 80 mg/kg level, while CAT was increased by 40, 80, and 160 mg FA/kg. On the other hand, MDA displayed low levels by FA, especially at 80 mg/kg level. The levels of SOD, CAT, and GPx were increased after HS, and the highest levels were displayed by FA feeding with a similar trend in MDA. However, the phagocytic (PA) and lysozyme (LZM) activities were decreased in tilapia after HS versus before HS, and dietary FA succeeded in improving PA and LZM in a dose-dependent regime. Dietary FA upregulated the expression of INF-γ, TNF-α, and IL-1β genes and downregulated HSP70 gene either before or after HS in a dose-dependent regime (linearly and quadratically P < .05). The analysis of polynomial regression revealed that dietary FA could be included at 81.25 to 98.75 mg/kg in tilapia diets. The obtained results reflect the necessity of using FA to counteract the impacts of HS on the antioxidative and immune responses in tilapia.