THE REPRODUCTIVE-BIOLOGY OF AN ENDEMIC CYPRINID, ZACCO-PACHYCEPHALUS,IN TAIWAN

Reproductive parameters including body weight-length relationship, con dition factor, gonadosomatic index (GSI) and fecundity of an endemic c yprinid, Zacco pachycephalus, were studied from October 1991 to Januar y 1993. Although the condition factor was similar between both sexes, GSI values of female (3.72 to 14.24%) were significantly larger than t hat of males (0.21 to 2.23%) during the major breeding season. The num ber of yolky eggs per fish ranged from 459 to 2059. Ovum size distribu tion, annual GSI value, and recruitment of juvenile fish indicated tha t Z. pachycephalus conducted two major spawning activities in spring ( February to April) and summer (June to August). The larger GSI value a nd number of yolky eggs in spring compared to those in summer implies that Z. pachycephalus has evolved a reproductive style by investing mo re energy in spring to avoid the damage of summer freshet on its recru itment success. The mating behavior of Z. pachycephalus is similar to that of other Zacco fishes.