Reproductive biology of thin sharpbelly, Toxabramis swinhonis Günther, 1873 in a shallow lake (Biandantang Lake) along the middle reach of the Yangtze River basin (China): implications for fisheries management

The reproductive biology of Toxabramis swinhonis, one of the most abundant bycatch species in freshwater fishery in China, was first reported based on 783 specimens collected in Biandantang Lake, central China from October 2016 to September 2017. The overall sex ratio (female/male) was 1.03:1, not significantly different from the expected value 1:1. Nevertheless, sex ratio varied with seasons: 1.32:1 in the early stage of the spawning season (March–April), while 0.46:1 in the later stage (July–August). The monthly succession of the average gonadosomatic index (GSI) and percentages of mature individuals co-indicated that T. swinhonis was a spring-summer (March–August) spawner. Further, the bimodal distribution of the size of eggs from one gravid ovary and histological analysis of mature gonads suggested that T. swinhonis was a multiple spawner with indeterminate fecundity and high degree of spawning asynchronicity. The sizes and ages at first maturity for females and males were 84.47 and 81.86 mm, and 1.62 and 1.56 yr, respectively. The batch fecundity (FB) of this species varied in a wide range from 2006 to 73592 eggs per fish with a mean value of 26487.15 ± 2675.61 (S.E.) eggs and increased with the increasing of the gonad weight (WG), eviscerated weight (WE), total length (LT) and age (A). Overall, T. swinhonis in Biandantang (BDT) Lake is characterized by high fecundity and prolonged spawning season, resulting in easy population explosion. Thus, to remove T. swinhonis moderately or release predator fish discreetly to control its population is proposed considering its reproductive characteristics.