Sesame Oil Cake as a Partial Soybean Meal Substitute in the Practical Diets of Juvenile Asian Seabass ( Lates calcarifer ): Nutritional Performance, Physiological Responses and Nutrigenomic Regulation

ABSTRACT The increasing reliance on imported soybean meal (SBM) in aquafeeds has intensified the search for locally available and sustainable alternative protein ingredients. This study evaluated sesame oil cake (SOC), an underutilized agro‐industrial by‐product in Bangladesh, as a partial replacement for imported SBM in diets for juvenile Asian seabass, Lates calcarife r. Five approximately isonitrogenous and isolipidic diets containing 0%, 5%, 10%, 15% and 20% SOC were formulated with progressive reductions in SBM. Juveniles (4.25 ± 0.27 g) were distributed among 15 tanks, with 20 fish per tank and three replicate tanks per treatment and fed for 60 days. Growth performance remained comparable with the control up to 15% SOC, whereas 20% SOC reduced final weight, weight gain, specific growth rates, and survival rate, while impairing feed conversion and protein utilization. Whole‐body crude protein was significantly lower in all SOC‐fed groups than in control. Higher SOC inclusion reduced haemoglobin, haematocrit and mean corpuscular haemoglobin, although most leukocyte indices remained stable. Fish fed 20% SOC also exhibited lower circulating total protein and lipase activity and elevated cholesterol, triglycerides, aspartate aminotransferase (AST) and alanine aminotransferase (ALT), indicating altered metabolic and hepatic function. Liver architecture was largely preserved at 5% and 10% SOC, whereas hepatocellular vacuolation and hypertrophy became apparent at 15%, with additional morphological alterations observed at 20%. At the transcriptional level, 20% SOC was associated with reduced expression of brain GH , hepatic GHR and IGF‐I and increased expression of skeletal‐muscle MSTN1 and hepatic SOD , whereas IGF‐II , MSTN2 and GPX showed no statistically significant treatment differences. Overall, SOC could be incorporated at up to 15% of the diet without compromising growth performance; reduced whole‐body protein deposition and hepatic alterations at higher inclusion levels warrant consideration. These findings demonstrate the potential of locally available SOC to partially reduce dependence on imported SBM in practical diets for juvenile Asian seabass.