Age, growth, mortality and recruitment of thin sharpbelly Toxabramis swinhonis Günther, 1873 in three shallow lakes along the middle and lower reaches of the Yangtze River basin, China

Despite being the most dominant and widespread small fish species in the lakes along the middle and lower reaches of the Yangtze River basin, Toxabramis swinhonis has been paid little attention by fisheries scientists and little is known about its population characteristics. For this reason, we estimated age, growth, mortality and recruitment of this species based on three shallow lakes, Biandantang Lake, Shengjin Lake and Kuilei Lake (BDT, SJH and KLH, respectively) in this region. A total of 13,585 (8,818 in BDT, 2,207 in SJH and 2,560 in KLH) individuals were collected during monthly sampling from July 2016 to September 2017. The results revealed that the age structures of T. swinhonis consisted of four age groups (0(+)–3(+)), with 0(+)–1(+) year old fish comprising more than 98% of the samples. Allometric growth patterns were displayed by fish from all sampling sites and the von Bertalanffy growth functions estimated were L(t) = 173.25 (1 – e(−1.20 (t + 1.09))): BDT; L(t) = 162.75 (1 – e(−1.20 (t + 1.08))): SJH and L(t) = 215.25 (1 – e(−1.20 (t + 1.12))): KLH, respectively. The rates of total mortality (Z), natural mortality (M) and fishing mortality (F) at BDT, SJH and KLH were computed as 5.82, 5.50 and 4.55 year(−1); 1.89, 1.87 and 1.75 year(−1); 3.93, 3.63 and 2.80 year(−1), respectively. Meanwhile, growth performance indices (φ′) were 0.68 (in BDT), 0.66 (in SJH) and 0.62 (in KLH), which indicated that T. swinhonis were overfished slightly in all study areas. Area-specific recruitment patterns were similar to each other, displaying evidence of batch spawning, with major peaks in April and August, accounting for 92.21% (BDT), 88.21% (SJH) and 88.73% (KLH) of total recruitment, respectively. These results showed that brief generation-time, fast growth rate, relatively high natural mortality rate and strong reproductive capacity (r-strategies) are reasons why this species became the most dominant species in many lakes of China.