Age, growth, and gonadal characteristics of adult bighead carp, Hypophthalmichthys nobilis, in the lower Missouri River.
Bighead carp were introduced into Arkansas in 1973 to improve water clarity in production ponds. Bighead carp subsequently escaped aquaculture facilities in the early 1980's and dispersed into the Mississippi and Missouri rivers. The first documentation of bighead carp reproduction in the Mississippi River system was in 1989. The population has increased in the Missouri River as is evident in their increased proportion in the commercial harvest since 1990. The effect of this exotic planktivore on native ecosystems of the U.S. has not been examined. Basic biological data on bighead carp Hypophthalmichthys nobilis in the Missouri River are needed to predict potential ecological problems and provide a foundation for manipulative studies. The objectives of this study were to assess age, growth, and gonadal characteristics of bighead carp in the Missouri River. Adult bighead carp in our sample varied from age 3 to age 7 and length varied from 475 to 1050 mm. There was a large variation in length at age, and overall bighead carp exhibited fast growth. For example, mean back-calculated length at age 3 was 556 mm. The sample was dominated by bighead carp from the 1994 year class. There was no difference in gonad development (i.e., gonadal somatic index, egg diameter) between winter and spring samples. Length of male bighead carp and GSI were not significantly correlated; however, females exhibited a positive linear relationship between length and GSI. In each ovary, egg diameter frequencies exhibited a bimodal distribution, indicating protracted spawning. Mean fecundity was 226 213, with a maximum fecundity of 769 964. Bighead carp in the Missouri River have similar life history characteristics to Asian and European populations. They have become well established in the Missouri River and it is likely that dispersal and population density will increase.