Grow-out of Yellowtail (Seriola quinqueradiata)

Grow-out

As mentioned earlier, most yellowtail culture is now carried out in floating or submersible cages. These are installed in areas where the salinity does not go below 16ppt. The optimal temperature range is between 24 and 29°C. Temperatures below 9°C and above 31°C are unsuitable for yellowtail culture.

Stocking densities range from 80–200 finger-lings/m³ in cages, depending on the size of the fingerlings. In net enclosures and ponds, much lower stocking rates of one or two finger-lings/m³ are adopted. They are generally fed on sliced or whole fish flesh. The same species used for feeding fry are used for feeding fingerlings and adult yellowtails. Even though some farmers use anchovies, it is not recommended, because continuous feeding with this fish can cause mortality as a result of the oxidation of the unsaturated fatty acids in anchovy flesh. Thiamine in anchovy flesh has been found to destroy vitamin B₁ in yellowtail. Feeding at the rate of 10 per cent body weight or 75–80 per cent satiety gives the best growth rates. The daily ration is given in two feedings for larger fish and three or four for smaller fish. The feed conversion is about 7 for fish that weigh up to1.5kg and 10 for fish up to 4kg, on a wet weight basis. On a dry weight basis, it is 2.1 and 3.0 respectively.

Though artificial diets are commercially available, very few farmers used them because of the high cost and the comparatively poor growth rates obtained. A suitable diet can be made from white fish meal making up about 70 per cent of the feed with 5–10 per cent gluten as a binder and a vitamin and mineral premix. Though the growth rate with this diet is less than with fresh fish, comparatively higher growth rates can be obtained by alternating the two types of feeds. Recent reports indicate that many farmers are now using a moist diet, prepared by mixing fish meat with a formulated powder.

Yellowtail grow rapidly in cages. Fingerlings stocked in May/June grow to 200–700g by August and 600–1600g by October. By the end of December they reach a weight of 700– 2000g. In some areas the smaller fish may be kept in the cages for a second year’s growth to about 2–3kg.