Dietary Potassium Supplementation Improves the Growth and Physio-Biochemical Responses of Genetically Improved Farmed Tilapia (Oreochromis niloticus) Reared inMedium-Saline Inland Waters

Abstract

Genetically Improved Farmed Tilapia (GIFT) (Oreochromis niloticus) is a promising species for inland saline waters (ISW). However, ISW is potassium-deficient compared to seawater. The growth and physio-biochemical responses of GIFT tilapia to dietary potassium chloride (1%) supplementation were evaluated after a 60-day trial. The different treatments were freshwater without KCl (FW×K0), freshwater with KCl (FW×K1), 10 ppt without KCl (10×K0), 10 ppt with KCl (10×K1), 15 ppt without KCl (15×K0), and 15 ppt with KCl (15×K1). Results demonstrated significant enhancement in growth parameters across all KCl-supplemented treatments, with the most pronounced effects in FW×K1 treatment. Dietary KCl supplementation improved the average daily gain by 18.7% and 13.0% in 10×K1 and 15×K1 treatments. Biochemical analysis revealed that increasing salinity progressively elevated oxidative stress markers in K0 treatments, with 15×K0 showing the highest superoxide dismutase (SOD) and catalase (CAT) activities. Similarly, metabolic enzymes (lactate dehydrogenase, LDH; malate dehydrogenase, MDH) and transaminases (aspartate aminotransaminase, AST; alanine aminotransaminase, ALT) exhibited significantly higher activities in high-salinity K0 treatments, indicating increased anaerobic metabolism and protein catabolism. Branchial NKA (sodium potassium ATPase) activity increased at higher salinities with 15×K0 (15.53 ± 0.82), demonstrating the highest activity among all treatment combinations. K1 treatments exhibited significantly lower NKA activity than those of the K0 groups, irrespective of the rearing salinity. KCl supplementation effectively reduced osmotic stress, thereby lowering the energetic costs of osmoregulation, metabolism, and protein resources for growth. These findings suggest that dietary potassium supplementation offers a viable strategy for enhancing GIFT production in potassium-deficient inland saline environments.