Abstract: Aiming to systematically analyze the gonadal development and fecundity characteristics of Gymnodiptychus pachycheilus, and their relationships with environmental factors in this fish species, sampling was conducted in the mainstem and tributaries of the upper Yellow River in Qinghai Province from May to June and October to November during 2023-2025. During the domestication period, dead specimens were used for sex identification. The gonadal developmental stages were determined by visual inspection. The gonadosomatic index (GSI) was calculated using the gravimetric method, and absolute fecundity (F) and relative fecundity (F_L) were determined. The correlations between these reproductive parameters and basic biological indicators were analyzed. Results showed that the gonadal development of G.pachycheilus could be divided into six stages, and the main spawning period was concentrated from May to June. The body length of sexually mature females ranged from 263 to 380 mm. The absolute fecundity was 7 592-14 047 eggs, and the relative fecundity was 61-90 eggs per gram. The peak gonadosomatic index (GSI) of males during the spawning season reached 5.55%. The egg diameter distribution indicated that the oocyte development followed a group-synchronous maturation pattern. Fecundity showed a significantly positive correlation with body length and body weight (P<0.05). Gymnodiptychus pachycheilus exhibited moderate fecundity and a group-syhchronous spawning pattern.

Key words: Gymnodiptychus pachycheilus, gonadal development, fecundity, gonadosomatic index (GSI), reproductive biology