金钱鱼(Scatophagus argus)体色发育及黑斑的形成过程

鱼类的体色图案作为外部形态最显著的特征之一,在动物生存与物种间的交流中起着重要作用。为探究金钱鱼（Scatophagus argus）体色发育及黑斑的形成过程,首先对成年金钱鱼鳍条中色素细胞进行显微观察,采用Olympus体视解剖镜观察了金钱鱼从胚胎色素形成期到仔鱼后期体表色素细胞的种类与分布特征,并跟踪观察了金钱鱼从稚鱼期到成鱼期主要图案黑斑的形成过程,同时对成年金钱鱼的黑斑和非黑斑皮肤进行透射电镜切片观察。结果显示,构成金钱鱼体色共四种色素细胞,分别为：黑色素细胞、黄色素细胞、虹彩色素细胞和红色素细胞,黑色素细胞在胚胎发育阶段最早发生,黄色素细胞和红色素细胞次之,而虹彩色素细胞发生最晚,直到仔鱼后期阶段才观察到。金钱鱼体色仔鱼期（0-24 dph）出现了有趣的变化过程：在0 dph（day post hatching）仔鱼体色较浅到1 dph仔鱼体色明显加深,而2-7 dph仔鱼的躯干部体色出现明显的褪黑现象,在8-24 dph阶段金钱鱼体色又出现了明显的复黑现象,并且在24 dph时通体发黑,在30 dph时虹彩色素细胞在皮肤中的大量出现并形成隐约可见的色素条带,直到幼鱼阶段（50 dph）形成清晰的黑色纵带条纹后不断演变成多个黑斑并在成年金钱鱼中稳定沉积的过程。透射电镜结果发现皮肤中黑色素细胞和虹彩色素细胞数量最多,分布最广。黑斑形成的关键原因是黑素小体和黑色素细胞大量聚集,虹彩色素细胞在其周围大量聚集并形成明显的包围界限。追踪观察了金钱鱼从胚胎色素发育、前期仔鱼、后期仔鱼、稚鱼、幼鱼和成鱼共六个阶段的色素沉积和体色变化过程,为金钱鱼野生群体的年龄鉴定提供了参考,并为进一步的金钱鱼体色改良提供理论指导。

DEVELOPMENT OF BODY COLOR AND FORMATION PROCESS OF BLACK SPOTS IN SPOTTED SCAT (SCATOPHAGUS ARGUS)

The body pigmentation on fish is one of the prominent features of their external morphology, and plays an important role in the survival and the communication among aquatic animals. To explore the development of pigmentation of black spots in spotted scat (Scatophagus argus), microscopic observation on pigment cells in the fin rays of the adult spotted scat was conducted with Olympus stereoscopic dissecting microscope. Types and distribution of pigment cells on surface of spotted scat from the embryonic pigmentation stage to the late larval stage were analyzed. The progress of main black spots of the fish from juvenile to adult stages was observed. In addition, spotted and non-spotted skins of the fish were examined in transmission electron microscopy. Four types of pigment cells were recognized, including melanocytes, xanthophores, iridophores, and erythrophores. Melanocytes occurred first in the embryonic development stage, followed by xanthophores and erythrophores, and iridescent pigment cells came last and disappeared in the late stage of larvae. Interesting variation occurred in the larvae (0-24 dph):in 0-1 dph, body color changed from light to dark, the trunk color of the larvae was obviously depigmented in 2-7 dph; and the pigment restored in 8-24 dph and the whole body became black in 24 dph. At 30 dph, many iridophores appeared in skin and formed dim pigment bands, clear dark vertical stripes started to show in the juvenile stage (50 dph) and finally they turned steadily into multiple black spots in the adult stage. As shown in transmission electron microscopy, most melanocytes and iridophores were widely deposited in the skin as the results of bulky accumulation of melanosomes and melanocytes, around which iridophores deposited and encircled. The course of pigment deposition and body color changes of the spotted scat could be recognized in six stages:embryonic pigment development, early larvae, late larvae, juveniles, juveniles, and adult fish. This study provided a reference for the age identification of wild populations of spotted scat and a theoretical guidance for the manipulation of body color of the spotted scat.