Sibship analysis revealed the reproductive strategy and current population status of the silver carp (Hypophthalmichthys molitrix) from the middle and lower reaches of the Yangtze River, China

Reproductive strategy and population status are crucial factors to understand species adaptation mechanism and to make suitable conservation decisions. In the present study, we investigated the reproductive strategy of the silver carp ( Hypophthalmichthys molitrix ) using microsatellite markers and sibship analysis on 476 offspring born in 2017 from the middle and lower reaches of Yangtze River in China. The results revealed that silver carp adopts a promiscuous genetic mating system with a balanced sex ratio 1:1 in the breeding population. Inferred partner numbers ranged from 1 to 4 for each parent, with more than half of the males (50.96%) and females (55.12%) mating with multiple partners. Sibship assignment revealed that reproductive success was relatively even among individuals for both sexes. The effective population size ( N e adj ) and census population size ( N c) in the middle and lower reaches of the Yangtze River in 2017 were 2686 and 8104, respectively, with a relatively high N e adj / N c ratio 0.33. The even reproductive success and relatively high ratio value of N e adj / N c suggest the absence of the sweepstakes reproductive success (SRS, the strategy offspring only from a few parents) in silver carp, which help maintain a relatively high genetic diversity in population. According to the result of larval (egg) resource survey, we estimated the census population of the silver carp in Yichang section, the main spawning ground, in 2017 to be 6498, which is approximately 58.71% of the historical record. Therefore, we recommend that conservation efforts for silver carp should be strengthened, especially focused on protecting the Yichang spawning ground to help restore its population.