FECUNDITY AND REPRODUCTIVE STRATEGY OF PTYCHOBARBUS DIPOGON POPULATIONS FROM THE MIDDLE REACHES OF THE YARLUNG ZANGBO RIVER

The Ptychobarbus dipogon of the Schizothoracinae subfamily, is an endemic economic fish species in Tibet Autonomous Region, China. Due to environment deterioration and invasion of alien species the population size of this species is decreasing; a study is urgently required to determine fecundity and reproductive strategy in order to conserve this natural resource. In this study, to investigate the fecundity and its relationship of body length, weight and age, we captured 1030 individuals in the middle Yarlung Zangbo River during two separate periods, one from February to March in 2013 and the other from February to June in 2014. The results showed that the standard length (SL) of males is concentrated in the 325—400 mm range, and the SL of females is above 375 mm. Sixty five females were at stages IV and V of sexual maturity, with SL 320—500 mm, weight 411.6—1328.0 g. Using the SL 50% method, the first female sexual maturity age was estimated to be 13.0 years and about 360.90 mm, while the first male maturity age was estimated to be 13.5 years and length 354.53 mm. The distributions of egg sizes, gonadal developmental stages and gonadosomatic indexes show that this species follows a synchronous spawning pattern concentrated in the period February to March, with an absolute fecundity at 3487 eggs, with a fecundity to SL ratio of 7.2 eggs/mm and fecundity to weight of 4.3 eggs/g. The absolute fecundity is positively correlated to the SL and the weight, but not significantly correlated to age. The overall male-female ratio was 1.23 鲶1. Suggestions for its conservation have been made based on its low fecundity, late maturity and short breeding period.