STUDIES ON THE REPRODUCTIVE BIOLOGY OF HEMICULTER TCHANGI FANG

Hemiculter tchangi Fang is an endemic fish in the upper Yangtze River, and mainly distribute in Sichuan Province and Chongqing City, China. At present, more and more researches have used endemic fish as indicative species to appraise the healthy of the river which they lived. Further more, due to the loss of habitat after the completion of the Three Gorges Project and other hydroelectricity projects, it was forecasted that the population sizes of the endemic fish might decreased sharply in the future. It is very urgent to make suitable countermeasures for the conservation and resource-recovery of those endemic species. So it is very important to study the biology of those fish. This paper deals with the reproductive biology of H. tchangi. One thousand and twenty three specimens were collected during November 2005 to February 2009 from the estuary of the Chishui River, the first-order tributary of the Yangtze River, which locates at Hejiang county of Sichuan Province. The results showed that the main spawning season of H. tchangi population took place from May to September. The minimum size of mature male was 108 mm in length and 9.4 g in weight, while that of mature female was 77 mm in length and 5.3 g in weight. Both of them were 1-year-old. There was significant different between the sex ratio in spawning season and non-spawning season. The sex ratio of males and females was 1.07:1 in the population, but there were more female individuals than male in the reproductive population (X2=9.643, P0.05, n=361). The body length of the mature individuals ranged from 77 to 216 mm, and most of them ranged from 101 to 180 mm (87.3%). The body weight ranged from 5.3 to 136.5 g, and most of them ranged from 10.1 to 80.0 g (90.3%). The population included 4 age-groups, some of them had got mature at 1-year-old, but most of them matured at 2-year-old. The gonadosomatic index (GSI) began to increase in March, and it reached to the peak in July. On the contrary, it decreased to the lowest in December. The egg diameter distribution in the ovary was unimodal at mature stage indicating that the fish was a total spawner as opposed to a batch spawner. The absolute fecundity of the mature females varied from 1164 to 41030 eggs, with an average of (11010?723)eggs. And the relative fecundity to body weight varied from 24.4 to 721.4 eggs per gram, with an average of (275.1?38.4)eggs per gram. The absolute fecundity of the mature females increased with body length, body weight and age. The absolute individual fecundity was curvilinear correlative to age, and linearly correlative to body length and body weight. But the indexes of the later two were not obvious. Statistical analysis of the total absolute fecundity at different age showed that 2 and 3 year-old fish took place the majority part. It means that the supplementary population dominates the breeding population. Our fieldwork demonstrated that the estuary of the Chishui River is a good environment for feeding and reproducing of H. tchangi.