| Survey on the fishes of early life history stages is an important area to carry out the studies in fish ecology and fisheries biology. But there is little published information on the identification of fish of early life history stages in the Yangtze River. Our objective is to determine diagnostic characteristics of species present in Yangtze River and its tributaries. The study consists of two parts. The first part is to develop a staging system so that the different species can be compared within the same period or stage. Early morphogenesis observations of 21 fishes were devoted to this purpose. Secondly, based on such a staging system, morphology of 105 fishes were compiled upon the collections of field sampling from 2000 to 2004 along the Yangtze River and the descriptions from scattered literatures about the early morphogenesis. In addition, spawning location, season and behavior of parental fishes were compiled as well. The useful diagnostic characteristics were extracted to develop the classifying system to discriminate the specimens to family, genus and species. The key points of the study are described as follows: 1. Early ontogeny is a dynamic process including the changes of morphology, physiology, behavior, etc, but the more common changes should be the regular transition of nutrition source. So the early life history of fishes is proposed to be divided into three periods, embryo, larva and juvenile, respectively in accordance with endogenous, exogenous nutrition and acquisition of particular adult diet. Hatching is not a suitable mark to delimit the embryonic and larval period. 2. The morphogenesis sequence is similar at family level, so that development of a standardized staging system at the family level should be possible. The embryonic period of Cyprinidae could be subdivided into 9 stages –activation, cleavage, blastulation, gastrulation, primary organogenesis, segmentation of caudal myotomes, eye pigmentation, finfold formation, an d body straightened. The larval period could be subdivided into 6 stages –one swimming bladder, differentiation of caudal fin, differentiation of dorsal fin and anal fin, differentiation of ventral fin, formation of caudal fin and formation of dorsal fin and anal fin. 3. Identification of early developing fishes should follow the next two steps. Firstly, the specimen could be identified to family level according to the striking features during different periods. Secondly, identification should be carried out among species of the same family and same stage. 4. The embryonic period should be generally subdivided into two parts, embryo with membrane or not. The key characters of embryo with membrane among families are attributes of membrane and yolk, but the identification of embryo without membrane depends on the attribute of yolk and the shape of the yolk-sac. Under the natural conditions, the developmental state is different between species as well. 5. During larval period, shape of body, pigment pattern, position and size of mouth, position of anus, shape of airbladder and existence of secondary fin were used to separate families. 5 types of body shape were defined according the ratio between body length, height, and width. 6. Interspecies identification of one family is based on meristic and morphometric characters and the pigment pattern. The useful characters include number of somites, total body length, distance from anus to the end of tail, diameter of eye, and body height, etc. 7. Some other characters, such as time of emergence, different reaches, water characters, microhabitat of early development, etc, can provide additional information on identification. The results could be more accurate if such information is available.
|
PDF Full Text Request