Restricted feeding and dietary energy levels affect liver structure in cultured Yellowtail Kingfish (Seriola lalandi, Valenciennes) at summer water temperatures

Excess dietary lipids may be stored as lipid droplets in liver hepatocytes where they cannot be transported from the cells. Yellowtail kingfish (Seriola lalandi, Valenciennes) are cultured using formulated feeds, putting them at risk of fatty livers. This study investigated the effect of restricted feeding (apparent satiation [100%] vs. apparent sub-satiation [80%]) and three different dietary energy levels (Diet 1 [19.0 MJ kg⁻¹ gross energy], Diet 2 [20.2 MJ kg⁻¹ gross energy] and Diet 3 [18.4 MJ kg⁻¹ gross energy]) on liver structure and function of sub-adult Yellowtail kingfish (1.87 ± 0.01, mean kg ±SE) over 84 days. Fish fed to 100% satiation had significantly (p < 0.05) greater weight gain than fish fed to 80% satiation. Both hepatosomatic index (HSI; %) and vacuolization levels of liver hepatocytes were unaffected by restricted feeding, but significantly (p = 0.016 and p = 0.039, respectively) increased with an increase in dietary energy. Fish fed high-energy diets showed extensive large hepatocyte vacuolization. Despite these adverse changes, results reported elsewhere showed that increased dietary energy level improved the overall growth performance and feed utilization of sub-adult Yellowtail kingfish compared with fish fed lower energy/lipid diets. Therefore, high-energy diets have the potential to be used in the production of Yellowtail kingfish.