赤点石斑鱼仔稚幼鱼的形态发育和生长

Morphological development and growth of the larvae, juveniles and young fish of Epinephelus akaara

通过赤点石斑鱼各个发育期的仔稚幼鱼连续取样 ,系统地观察了仔稚幼鱼各个发育期的形态变化及生长特征 ,并进行描图。赤点石斑鱼初孵仔鱼全长 1.35～ 1.4 5mm。稚鱼第 6～ 7d长出特别伸长的背鳍第 2鳍棘和腹鳍棘 ,其长度与全长之比在第 16～ 18d、全长 11mm左右时达到最大值 ,接近 5 0 %。这一形态特点是石斑鱼属仔稚鱼期特有的。以后随着个体的生长和其他鳍棘的伸长 ,这一比例逐渐减小 ,直至小于其他鳍棘 ,这是稚鱼完成变态成为苗种的重要标志。最早完成变态的稚鱼须在孵化后第 35d ,全长 30mm以上 ,但到第 4 5d时 ,全长 2 4mm的个体也可以完成变态。即使在相同的环境条件下 ,仔稚幼鱼的个体大小差异也很大 。

The newly hatching larvae, juveniles, young fish of Epinephelus akaara were sampled every 3 5days along with growth of the fish to trance and observe the characteristics and growth. The newly hatching larvae were 1.35 1.45 mm in T.L. and might be the smallest one of the newly hatching larvae of the marine fish which artificial propagation had been carried out. The most characteristic feature of the fish (and all species belonging to the genus Epinephelus) was extraordinary prolongation of dorsal second and ventral spines appearing when the larvae were 7 8 days old and about 4 5mm inT.L. The ratio of these spines to T.L. attain its maximum (about 0.5) when the fish were 16 18days old and 11mm in T.L. Thereafter the ratio decreased along with growth of fish and elongation of other spines till the dorsal second and ventral spines were shorter than other spines and this was the important symbol moaned metamorphosis was completed. The earliest completing of metamorphosis occurred when the fish were about 35 days old and more than 30mm in T.L., but when the fish were 45days old, individuals less than 24mm in T.L. could complete metamorphosis. The individuals showed remarkable divergences in growth even under the same rearing condition and there were the later stage the more remarkable divergences. Under the condition of 25℃ 29℃ in water temperature the fish whose showed rapidest growth attained 2.5mm, 2.9mm, 5.1mm, 9.2mm, 15.7mm, 25.8mm, 28.2mm, 35.5mm, 41.2mm, 70.4mm, 83.5mm in T.L. in 3, 5, 10, 15, 20, 25, 30, 40, 54, 68 days respectively.