Schizochytrium as a replacement for fish oil in a fishmeal free diet for jade perch, Scortum barcoo (McCulloch & Waite)

A 10-week trial was conducted to determine the response of juvenile jade perch Scortum barcoo on the replacement of dietary fish oil (FO) in a fish-meal free diet. Three iso-nitrogenous, isocaloric and isolipidic diets were formulated, each containing a different primary fat source: FO, linseed oil (LO), and a mixture of Schizochytrium and LO. The substitution of FO with the mixture of Schizochytrium and LO did not cause a difference in growth. However, there was an 8% reduction in weight gain in fish fed dietary LO, indicating that juvenile jade perch do require a minimal concentration of dietary n-3 highly unsaturated fatty acids (HUFA). Fish fed the Schizochytrium diet stored more efficient n-3 HUFA and in particular DHA in their flesh, and retained a higher fillet recovery compared to fish fed FO. In addition, we demonstrated that jade perch are able to produce both n-3 HUFA and n-6 HUFA when dietary PUFA are present. Fish fed the LO diet for 10 weeks contained the lowest amount of n-3 HUFA in fillets among dietary treatment groups. However, feeding these fish the Schizochytrium diet for an additional 4 weeks increased the n-3 HUFA content towards the same concentration of n-3 HUFA found in the flesh of fish fed FO, without affecting the sensory properties of the fillets. In contrary, feeding the Schizochytrium diet for a continuous period of 14 weeks lowered overall sensory property scores.