Polka-dot grouper, Cromileptes altivelis, can utilize dietary fat efficiently

Polka-dot grouper, Cromileptes altivelis, a highly-prized fish in Asian live fish markets, is a slow-growing species. Long-chain (LCF) or medium-chain fatty acids (MCF) were fed to polka-dot grouper (14 g initial weight) for 8 weeks to see if growth could be stimulated. Five dietary treatments were compared: a control diet with low fat (56 g kg−1) or diets that contained either moderate (150 g kg−1) or high (300 g kg−1) supplements of fat that were added either as olive oil for the LCF or coconut oil for the MCF. Control fish performed well; they grew at 2.2 g week−1, had a dry matter feed conversion ratio of 1.0 and deposited dietary protein and energy at efficiencies of 25 and 26%. Fish fed LCF at moderate levels performed better than controls but, when fed LCF at high levels or MCF at any level, their performance was inferior to controls. We conclude that dietary supplementation with 150 g kg−1 of LCF stimulates growth and improves protein retention of polka-dot grouper whereas higher levels, or the same or higher levels of MCF, depress performance.