斑点马鲛仔稚鱼的形态特征

THE MORPHOLOGY AND CHARACTERISTICS OF THE SPOTTED SEER SCOMBEROMORUS GUTTATUS(BLOCH&SCHNEIDER)

本文是通过大面积调查,用浮游生物网在南海区采到的斑点马鲛仔稚鱼,观察研究的结果。采到的最小仔鱼体长4.15毫米,其外形已显现出马鲛鱼类仔鱼的一般外貌,体呈延长形,尾部较细,肛门位于体中央略前,头较短钝,肌节在48—49个左右。尾部下缘出现一列小星状黑色素。体长达4.70毫米时,前鳃盖骨出现2个小棘。当体长达5.00—5.50毫米时,背鳍膜前端出现一个黑色斑,随着鱼体的长大,此黑色斑也逐渐增多变成彼此靠近的数个色素丛。发育到第一背鳍棘出现后,黑色素丛仍分布在棘的鳍膜间。

The larvae of the Spotted seer Scomberomorus guttatus were obtained by plankton net tows from Beibu(Tonkin)gulf and Northern part of Nan Hai in 1963 and 1965.The spotted,seer is a warm water species in general they live in open seas.In the breeding season they usually aggragate in shoals and migrate towards the shallow waters along the mainland and near the estuary,where the water temperature was 23.0-26.0℃,the salinity 32.00-34.46‰and 22.0-27.0℃,the salinity 20.00-29.00‰respectively in Nan Hai and the East China sea.The adult does not exist in the Yellow sea.The smallest larva is 4.15mm.in body length,it is elongate and with a small yolk-sac and a single oil globule situated in posterior.The fin fold islower,colourless and transparent,there are a few stellate melanophores along the ventral margin of the tail region.The body length of the postlarvae is 4.70mm.There are two small spines on the preopercular,with a few stellate melanopbores situated at the ventral edge of the tail region.Specimens which are 5.25mm.in body length have a black spot on the anterior of dorsal membranous,and the preoperculum spine are four.When the body lengh is 7.50mm,the black spot is on the dorsal fold which has three clusters.The upper jaw prominently longer than lower jaw.When the upper jaw is apparently visible,the maxillary bone changes its shape as a bow.At this stage,the occipital spine appears as a small tower,the dorsal spines occurs and the black pigments can be found among the membranuous.The postlarvae are 8.75mm.in body length,the maxillary bone changes into the normal shape,and a post temporal spine appears in the shoulder region.While the juveniles reach 8.64mm.in body length,there arc a number of stellate melanophores on the top of the head and snout,the occipital spine and post tamporal spine are still evident.