EARLY DEVELOPMENT OF ZACCO PLATYPUS (CYPRINIFORMES: CYPRINIDAE) DISTRIBUTED IN BEIJING

Pale chub Zacco platypus (Temminck Schlegel, 1846), a kind of small cyprinid fish, widely distributes in the East Asia including east part of China, Japan and Korea Peninsula. This fish is always found in rivers and streams, especially in the swiftly running waters. In breeding season, the male will express remarkable sexual dimorphism. Numerous sharp nuptial tubercles can be found on the head (especially jaws) and fins. Recently, the populations of Zacco platypus are shrinking down in many places in China due to over-capture, environment change and pollution. Under this background, understanding the life history of Zacco platypus will be very helpful for future conservation and sustainable use. Therefore, we observed the early development of Zacco platypus collected from the Huaijiuhe River in Beijing. Fertilized eggs were obtained through dry method of artificial fertilization, 10-15 fertilized eggs in the process of granule development were randomly selected. The processes and characteristics of early development have been observed and documented under the microscope. The mature eggs were spherical in shape, and the average egg diameter was 1.04 mm. At average water temperature of 23.0℃ (17.1-28.0℃), the early development from fertilization to hatch took total 73h01m and 1682.3℃h accumulated temperature. The embryonic development took 37min to develop into blastodermic disc through discoidal cleavage; and then took another more than 30min to develop into two-cell. Mulberry occurred about 4h after fertilization, multi-layer stack such as morula blastomeres, animal pole extremely high uplift. Blastula finished at 6h22min after fertilization, and embryonic development was into gastrula about 6h18min after late blastula. Blastopore formed around 19h after fertilization, and then myocomma appeared when blastopore closed. Eye capsule formed at 22h46min after fertilization. 25h27min after fertilization, tail bud appeared on the ventral posterior embryo. Tail fin formed around 29h after fertilization. The embryonic development took 1h to develop into effect of muscle after tail fin, embryo body could be seen tic regular intermittent, spherical yolk sac cylindrical front, rear section with the further growth of the caudal fin was elongate. Heart fully formed and slowly beat at 38h35min after fertilization, average heart beat was 84 times per min. The embryonic development took around 73h from fertilized egg to hatch, and then took 6.5 days to develop into flexion larvae. The development speed was slower in larvae than that in embryonic stage. Flexion larvae died in large scales may be because limited conditions of artificial cultivation and lack of energy supply when coexistence of mixed nutrition. Comparing to 21 other cyprinid species, development time of Zacco platypus was longer than that of seven species. Total development time of Zacco platypus was slightly longer than sympatric species Opsariichthys bidens, and obviously longer than Zacco temminckii. We also found the development speed before hatch of northern population was faster than southern one, but slower after hatch.