Effects of varying protein and lipid levels, with or without the addition of L-carnitine supplementation on growth performance and nutrient utilization of Asian Seabass (Lates calcarifer) reared in recirculating aquaculture system

Abstract

In a 60-day feeding trial, the impact of supplementing L-carnitine to low protein high energy (LPHE) diets was investigated. The study focused on the growth performance, nutrient utilization, health status, and fatty acid profile of Asian seabass (Lates calcarifer) reared in a recirculating aquaculture system (RAS). Seven iso-energetic (∼4600 Kcal/kg) diets with varying levels of protein and lipid, both with and without L-carnitine supplementation viz. control- (47/10), T1(44/12), T2(41/14), T3(44/12 with L- carnitine 0.05%), T4(44/12 with L- carnitine 0.1%), T5-(41/14 with L- carnitine 0.05%), T6 (41/14 with L- carnitine 0.1%) were prepared. L. calcarifer fingerlings with an average weight of 5.2 ± 0.1 g were randomly allocated to each treatment in triplicate, with 50 fingerlings per replicate. The fingerlings were fed three times a day until they reached satiation. The findings of present study revealed significant variations (P < 0.05) in final weight, weight gain, Specific Growth Rate (SGR), Feed Conversion Ratio (FCR), Protein Efficiency Ratio (PER), and Thermal Growth Coefficient (TGC) among different treatments, demonstrating linear trends. Fish survival rates across treatments showed no significant variations (P > 0.05) and lacked both linear and quadratic trends. Dietary treatments did not have an overall significant effect (P > 0.05) on whole-body moisture and crude protein contents of seabass, showing no discernible linear or quadratic trends. However, notable differences (P < 0.05) were observed in whole-body lipid and total ash contents, displaying linear and quadratic trends. The n-6 polyunsaturated fatty acid (PUFA) and n-3 PUFA content exhibited an overall significant impact due to dietary variations, showing both linear and quadratic trends. Cholesterol, triglyceride, and cortisol contents showed statistically significant overall differences, with discernible linear and quadratic trends across treatment groups. Superoxide dismutase (SOD) and catalase (CAT) activity also demonstrated an overall significant effect, accompanied by a linear trend. In conclusion, adding L-carnitine at a 0.1% concentration to diets containing 44% protein and 12% lipids boosted both growth performance and antioxidant response of L. calcarifer.