Reproductive biology of Gymnocypris przewalskii in Quanji River, Qinghai Province

Background During 2023, monitoring efforts using passive integrated transponder (PIT) tags revealed intriguing grouping behaviors within the spawning populations of Gymnocypris przewalskii in Qinghai Lake.

Objective This study aimed to investigate the reproductive biology characteristics of G. przewalskii populations following the emergence of grouping phenomena.

Methods Between May and August 2023, a sample size of 552 G. przewalskii specimens was gathered from Quanji River. Extensive reproductive biological analyses were performed, including examination of gonadal tissue, determination of initial sexual maturity lengths, assessment of egg diameter distributions, calculation of gonadosomatic indices, estimation of fecundity, and establishment of age structures.

Results The mean body length of the sampled G. przewalskii was (224.5±20.4) mm, with an average body mass of (179.5±62.1) g. Within this cohort, 253 female individuals averaged (240.4±28.7) mm in body length, and (140.9±76.9) g in body mass, while 299 males measured (188.8±63.0) mm in body length, and weighed (159.3±55.6) g on average. Females spanned ages 4 to 11 years, with 4 years old and 5 years old predominating at 78.6%, whereas males ranged from 3 to 6 years old, with 3 years old and 4 years old comprising 86.5% of the sample. Utilizing the L₅₀ methodology, the onset of sexual maturity was established at 167.5 mm for females and 154.6 mm for males. Average egg diameters across stages Ⅱ−Ⅴ were (0.98±0.05) mm, (1.45±0.02) mm, (1.63±0.05) mm, and (1.88±0.05) mm, respectively. Spawning activity peaked in June and July, classifying G. przewalskii as anadromous spawners. Female maturity coefficients rose steadily from May, peaking in July before declining in August. Absolute fecundity varied between 720.0 and 16080.0 grains per female, averaging (4261.4±3343.38) grains, with relative fecundity ranging from 9.1 to 131.4 grain/g and averaging (29.4±10.3) grain/g. For females, absolute fecundity (AF) was logarithmically related to body length (L), with the equation AF=14985lnL−76978 (R²= 0.7688, P<0.0001 ); absolute fecundity (AF) was also logarithmically related to body weight (W), with the equation AF = 5078.9lnW−20610.0 (R²= 0.848 0, P<0.0001 ). Female body length (Y_♀) had a strong correlation with body weight (W_♀) (R² =0.9085, P<0.0001 ), with the equation Y_♀=0.015 3W_♀²−5.2191W_♀+516.6300; male body length (Y_♂) also had a strong correlation with body weight (W_♂) (R²=0.8653, P<0.0001 ), with the equation Y_♂=0.0015W_♂²−0.2068W_♂ +53.7840. Otolith sections of G.przewalskii were irregular horseshoe-shaped, with the central area appearing darker under transmitted light, nearly circular; the outer area of the central zone exhibited irregular alternating light and dark rings under transmitted light.

Conclusion After the grouping phenomenon appeared in the migrating population of G. przewalskii in Qinghai Lake, the migrating population in Quanji River did not show obvious characteristic changes. This study provides scientific evidence for the conservation and sustainable use of G. przewalskii in Qinghai Lake.