Growth, physiological and histopathological responses of red hybrid tilapia (Oreochromis sp.) fed dietary protein levels under saline groundwater conditions

It is important to define the exact protein requirement to ensure the economic and environmental sustainability of tilapia aquaculture, particularly in saline systems, where osmoregulation augments metabolic demand. This experiment used a holistic, multi-biomarker approach to identify the optimal dietary crude protein content for juvenile red hybrid tilapia (Oreochromis sp.) reared in saline groundwater (33 ppt) in concrete tanks. Isoenergeticdiets containing 25, 30, 34, and 38% crude protein were fed to the fish for a 90-day period. Although the 38% CP diet produced higher growth performance and feed efficiency, it resulted in a marked physiological trade-off, represented by a drastic reduction in survival (51.1%). Detailed hemato-biochemical and histopathological investigations revealed the hidden physiological cost of this high-protein diet: systemic dysregulation, including severe anemia, hypercholesterolemia, hepatic steatosis and necrosis, branchial damage, and activation of the intestinal immune response. In contrast, the 34% CP diet supported strong growth, maintained high survival (75.55%), and preserved homeostasis across physiological and tissue-health variables. Thus, we can deduce that a dietary crude protein level of 34% offers the balanced zootechnical performance, physiological integrity, and production sustainability for juvenile red hybrid tilapia cultured in saline concrete tanks.