真鲷人工繁殖与苗种培育的初步试验

THE PRELIMINARY STUDY ON ARTIFICIAL PROPAGATION AND FRY CULTURE OF PAGROSOMUS MAJOR

广东遮浪海区真鲷于10月至翌年3月繁殖.成熟亲鱼用LRH-A和HCG注射均可自然产卵.其仔鱼以轮虫作开口饵料.后逐步改喂卤虫无节幼体和鱼虾肉浆碎片.其成活率仔鱼期高,由仔鱼期向稚鱼期转化时成活率降低.经205天培育,其平均体长为135mm.平均体重100g.

The breeding season of Pagrosomus major in the Zhelang sea area of Guangdong is from Oct. to Mar. in next year. The flourishing period is from mid-November to mid-January. So long as the maturity degree of brood fish is qualifed, to inject the spawners with LRH-A of 30--40ug/kg or HCG of 1000 - 1500 lU/kg (the dose for injecting the milter being half of that for the spawner), whether injecting once or twice (the time interval being 24-48 hours), the result of natural propagation may be gained, when the water temperature is 18. 5- 19- 5 C,. the response hour is 18-20 hours.The fertilized eggs of Pagrosomus major float on the water surface. The unfertilized eggs sink at the water bottom. When the water temperature is 18-19- 5 'C. the specific gravity of seawater is 1.023. Under the normal water quality, the larvae will hatch out in 40-41 hours. Whether hatching in stagnant water or in slightly flowing water, comparatively high hatching rate may be gained. The Larva just hatched out is 2. 3-2- 6 mm in Length. It lies on its back or lies on its side on the water surface After 2-3 days, the larvae scatter in the water layers and begin to eat the small-sized Brachionus plicatilis. After 25 days in growing, when the larvae are 7 - 8 mm in length. It is begun to feed them the nouplius of Artemia salina. After 40 days in growing, when the larvae are 12-13 mm in length. It is begun to feed them the bits of fish meat or shrimp meat. Brachionus plicatHis and Artemia salina are preferable to be soaked for 4-6 hours in unsaturated fatty acid so as to raise the 20: 5W3 and 22.- BW3 of unsaturated fatty acid.The survival rate of the larvae within 5 -10 days in growing may be as high as 80% or above. The survival rate of the larcae within 15-20 days in growing begins to drop. After 30-35 days in growing, when they are 8-10 mm in length and transform form the larval stage into the young fish stage, because of the forming of canine teeth, the larvae cruelly eat one another, the survival rate drops to around 45% - 50%. Thereafter the survival rate rises gradually. After 100 days in growing, when they are 45 mm in length, so Long as the water quality is fresh, the management is suitable and the operation is correct, the survival rate may be steady.This time, through 205 days' culture, the average body length of Pagrosomus major reaches 135mm, the overage body weigth reaches 100 g. In the culture period, after 30 days in growing the growth rates of the body length and body weight of Pagrosomus major all increase linearly with the increase of their monthly age. The interrelation between the body length and body weight is a function of power: W = 0. 000867 L2.433or logW = 2. 433. log - 3. 062 (W in g, Lin mm).