A PRELIMINARY STUDY ON THE REPRODUCTIVE BIOLOGY OF COREIUS GUICHENOTI (SAUVAGE & DABRY DE THIERSANT, 1874) IN THE MIDDLE AND LOWER STREAM OF JINSHA RIVER, CHINA

Coreius guichenoti (Sauvage & Dabry de Thiersant, 1874) is an endemic and commercially important fish in the upper Yangtze River, and its spawning grounds are mainly distributed in the main stem of the middle and lower reaches of the Jinsha River (which belong to the upper streams of the upper Yangtze River) and its tributary, the Yalong River. However, due to dam cascade in the Jinsha River and Yalong River, the spawning and feeding habitats of C. guichenoti have changed dramatically, leading to a significant decline in the population of endemic fish over last decade. To protect the fish resource ofC. guichenoti, many protective plans, including captive breeding, have been designed and implemented. It is very important to study their reproductive biology to provide basic information for captive breeding. Thus, based on the parent fish of C. guichenoti collected at the Jiaopingdu spawning ground from 2013 to 2014, and at the Jinanqiao-Qiaojia river located in the middle and lower reaches of the Jinsha River from 2006 to 2014, the reproductive biology of C. guichenoti was studied. The results showed that the minimum total length, weight, and age of mature females were 330 mm, 441 g and 4 years, respectively, while those for the mature males were 352 mm, 396.6 g and 3 years, respectively. The age and total length at which 50% of the individuals reached sexual maturity were 4.32 years and 406 mm for females, and 4.44 years and 412 mm for males, respectively. The sex ratio between male and female in the Jiaopingdu spawning ground was 1.37﹕1, which was not significantly different from 1﹕1, and the age structure of sexually mature individuals were 4—7 years in female and 3—7 years in male. The mean gonadosomatic index (GSI) displayed the highest value of 10.55% for female and 3.45% for male in 6-year-old for both genders. The average egg diameter ofC. guichenoti was 0.16 cm, and the egg diameter distribution displayed two groups of ooctes within the same ovary. The absolute fecundity of mature female varied from 4055 to 137900 eggs with an average of 22817 eggs, while the relative fecundity ranged from 5 to 73 eggs per gram with an average of 20 eggs per gram. Moreover, the absolute fecundities for the 75.68% individuals were between 10000 eggs and 30000 eggs, while the relative fecundities for the 70.27% individuals were between 15 and 20 eggs per gram. The absolute and relative fecundities of mature female increased with the total length and body weight, and the relationships between the total length and body weight and the absolute fecundity or relative fecundity could be represented by an exponential function (absolute fecundity) or quadratic function (relative fecundity). The research results can provide important basic data support for the protection of C. guichenoti fish resources in the Yangtze River Basin.