美洲鲥仔、稚、幼鱼的形态发育与生长特征

Morphological development and growth of American shad(Alosa sapidissima) at larvae,fry and juvenile stages

通过对美洲鲥(Alosa sapidissima)仔、稚、幼各发育期的连续取样,系统观察了仔、稚、幼各期的形态变化及生长发育特征。结果显示:在水温(20±1)℃下,初孵仔鱼全长(6.75±0.60)mm;2日龄仔鱼即开口摄食,进入混合营养期;4日龄仔鱼卵黄囊吸收完毕进入晚期仔鱼阶段,完全依靠外源物质获取能量,主要以鳔室、脊椎形成及各鳍的分化与形成为主要标志;培育至36d,仔鱼鳃盖后缘及脊椎骨两侧线有少量鳞片状突起,标志美洲鲥结束仔鱼期进入稚鱼期;培育至65d,仔鱼身上鳞片基本长出,腹膜闭合,美洲鲥完成变态成为幼鱼。仔鱼培育期间,除了严格控制培育水温在(20±1)℃外,2日龄仔鱼开口后就应及时投喂轮虫类开口饵料,密度为5～10ind/mL,这是苗种培育中不可忽视的重要环节。稚鱼期间在主食枝角类、桡足类的同时进行驯食。本实验采用特制缓沉饲料及时驯化转食再过渡到全部摄食人工浮性膨化颗粒饲料,驯食时间为21d,驯食是成功进行人工池塘养殖的关键所在。本研究旨在探讨提高美洲鲥早期培育过程中的成活率及成功进行池塘养殖的可行性。

The morphological development of American shad（Alosa sapidissima） in their early life cycle was observed and classified into larvae,fry and juvenile stages.The size of young fish during developmental stages was recorded.The larvae were（6.75±0.60） mm in total length at hatching.The feeding activities began at 2 days of age when water temperature was maintained at（20±1）℃,and they exhibited multiple feeding behaviors.Larval American shad finished yolk-sac absorption 4 days after hatching.At this stage,swim bladder,vertebrae and fins presented,and larvae required exogenous food.After 36 days,a few scales occurred at the back of the operculum and on the lateral lines of fish,which indicated that larvae had metamorphosed into fry.Thereafter,fry developed into juveniles after 65 days,and their bodies were mostly covered with scales and their peritoneum completely developed.Understanding the morphological development of these early life stages could contribute greatly to the subsequent successful culture of American shad.Research results indicate that temperature,water quality,and initial feeding strategy are most critical to fish farming of this species.Therefore,the following criteria are recommended：water temperature should be controlled at（20±1）℃ during the early culture of this species;larval fish should be fed with rotifers at a density of 5-10 ind/m.L on the second day after hatching;cladocerans and copepods are the most suitable foods for fry of American shad.In addition,we developed a semi-buoyant diet as an additional food supply for the fry.We succeeded in training A.sapidissima fry to feed this artificial food for 21 d until they fed commercial products（floating pellets）.Weaning of fry from the artificial food assures the success of pond culture of this species.