POPULATION BIOLOGY OF TOPMOUTH GUDGEON (PSEUDORASBORA PARVA) IN THE BAO'AN LAKE Ⅳ. POPULATION DYNAMICS

The paper dealt with the population dynamics for P.parvain the 1# experimental enclosure (3.33hm2) of the Bao'an Lake. The single mark-recapture method was used to estimate the population size of the fish sampled by the trapnets (namely net weirs). The population number ranged from 13,462—81,725ind(0.40—2.45ind·m-2)during the period of October 1995 to November 1996. A large variation in year class strength was apparent. The 1996 year class was particularly strong; an extrapolated 70,089 ind of this year class was present in May, and this figure decreased to 21,631ind in November compared with 14,431ind of the previous 1995 year class at the same stage in the life history. Mean monthly instantaneous mortality rate of 1996 year class was higher in summer, and the mortality of 1994 year class sharply increased in late May, and the remaining fish of this year class died after the spawning season. Annual mortality for 1995 year class was 71.7%, and monthly instantaneous mortality rate increased during summer. The population locomotor activity level was commonly influenced by water temperature,but it may be mainly affected by spawning behavior in spring(March to May). in spring. Population fecundity of P. parva in the 1# experimental enclosure in 1996 was 4.05×106 eggs, of which 0+ age group (1995 year class) contributed 85.7%.