Dietary fish oil (FO) was replaced by olive oil (OO) in young yellowtail Seriola quinqueradiata to investigate its effects on growth, muscular fatty acid composition and prevention of color deterioration of dark muscle during storage. Yellowtail were fed one of four diets, where FO (80 g/kg diet) was replaced by OO (0, 25, 50 and 100%) for 40 days. No significant difference in growth was seen among the diet groups. In addition, these experimental diets did not affect the proximate compositions of the dorsal muscle, ventral muscle and the liver in these fish. Serum total protein, glucose and total cholesterol levels did not show significant differences; however, serum triglyceride levels were significantly higher in fish fed 50 and 100% OO diets. Fatty acid composition of ventral muscle reflected the composition of the respective diets. Dark muscle discoloration was reduced in fish fed OO diets after 12 to 18 h during storage at 4°C. Furthermore, the redness value of fresh dark muscle increased depending on the extent of FO replacement. These results indicate that the partial or total dietary replacement of FO with OO prevents discoloration of dark muscle without affecting the growth of young yellowtail after 40 days of feeding.

To improve the commercial value of cultured yellowtail, the following two experiments were conducted. In theˆrst experiment, the anti-oxidant eŠects of yuzu Citrus junos juice on prevention of dark muscle discoloration during storage in yellowtail Seriola quinqueradiata were investigated. Yellowtails were fed one of four diets supplemented with yuzu juice (0, 12.5, 25 and 50 mL/kg diets) for 40 days. Growth performance was not signiˆcantly diŠerent among the dietary groups. Dark muscle discoloration was reduced inˆsh fed yuzu juice-supplemented diets during storage at 4°C. These results indicate that yuzu juice-supplemented diets prevent dark muscle discoloration without aŠecting the growth of young yellowtail after 40 days of feeding. In the second experiment, the ac-Experimental diets Control Yuzu 12.5 Yuzu 25 Yuzu 50 Ingredients (g/kg) Fish meal 1 650 Krill meal 2 50 Pollack liver oil 3 80 a-Starch 80 Cellulose 75 Vitamin mixture 4 20 Mineral mixture 5 20 CMCNa 20 Guar gum 5 Yuzu juice 0 12.5 25 50 Water 450 437.5 425 400 Proximate composition (g/kg) 6 Crude protein 501 496 499 495 Crude fat 166 162 159 165 Crude ash 123 120 116 117