Biological characteristics of Ctenopharyngodon idellus in middle and lower reaches of Pearl River

In order to find out the current status of the population structure and growth characteristics of grass carp (Ctenopharyngodon idellus) in the middle and lower reaches of the Pearl River, we have investigated the grass carp population from 2019 to 2020. The results show that the body length of grass carp was 103−665 mm average: (347.89±96.73) mm. The body mass was 21.4−6 650.0 g average: (986.87±842.96) g. The population age was of 0⁺−5⁺, and the dominant age was 1⁺−3⁺, accounting for 92.8% of the total number of samples. The body length had a significant power function relation with body mass for uniform motion pattern. The growth could be described by Von Bertalanffy equation with the growth parameters: L_∞=1187 mm, k=0.128, t₀=−0.282, W_∞=31 344.51 g. The index of length growth performance (φ) of grass carp was 5.26, and the growth inflection age was 8.29. The total mortality rate, natural mortality rate, fishing mortality rate and exploitation rate were 0.58, 0.29, 0.29 and 0.5, respectively. The sex ratio (Females/Males) was 1.07: 1. The sexual maturation was mainly at Stage II. Compared with the previous data, the growth performance and fecundity of grass carp all showed a decline tendency; the population structure tended to be miniaturized. In order to promote the recovery of grass carp resources in the middle and lower reaches of the Pearl River, it is recommended to reduce the fishing intensity. Besides, the catch body length should be greater than 791 mm and the mass should be greater than 9 279.11 g.