STUDIES ON SEVERAL ASPECTS OF GROWTH OF SILVER CARP AND BIGHEAD CARP IN LAKE DONGHU, WUHAN

Silver carp, Hypophthalmichthys molitrix, and bighead, Aristichthys nobilis, form the dominant fish populations in Lake Donghu. In 1979—80, the author studied the growth of silver carp and bighead carp by back calculation, including their growth patterns, instantaneous growth rates(G), differences between males and females in growth, etc. The results showed that the growth patterns of the two species can be described by von Bertalanffy growth equation pretty well, the parameter values of which for silver carp were l∞=99.8cm., W∞=17104g., K=0.3040, t0=0.4821yr.; and those for bighead carp were l∞=117.6cm., W∞=29311g., K=0.3088, to=0.5392yr. The instantaneous growth rates for the two species declined graduallly with age and varied at the same age for their various year classes to some degree, coefficients of variation for them being correlated positively with age. There were no significant sexual differences in both length and weight increases for the two species of fish. After comparing and analysing the results of this research and relevant studies, the author explained that the occurrence of growth inflexion at the age of four or so in silver carp and bighead was determined by their size rather than by their age at that time. It was observed that the effects of growth compensation existed in various year clsses of the two populations as well as in various individuals of the same year class. And in the process of growth for the two species, the changes of their instantaneous growth rates were apparently in correspondence with the changes of their condition factors(K). The parameter walues derived in this research can be applied to fishery assessment.