BIOLOGICAL CHARACTERISTICS OF CLUPANODON THRISSA IN PEARL RIVER ESTUARY

In order to understand the biological characteristics and resource status of Clupanodon thrissa in the Pearl River, a total of 408 samples of C. thrissa were collected monthly from October 2020 to September 2021 in Guangzhou section of the Pearl River Estuary. The age composition, growth and reproductive characteristics of C. thrissa were analyzed according to the methods such as biological measurement, age structure analysis and histological observation. The results showed that the average standard length and body weight of females were (173.60±17.10) mm and (92.30±24.37) g, respectively. While the average standard length and body weight of males were (155.94±15.10) mm and (65.81±19.97) g, respectively. The population age was ranged from 0⁺ to 5⁺, and the dominant age was 1⁺—3⁺, accounting for 89.03% of the total number of samples. There was power function relationship between standard length and body weight of C. thrissa: W=1×10^–5L^3.0525 (R²=0.9057), indicating that it was uniform growth pattern. Von Bertalanffy growth equation was used to describe the growth characteristics of C. thrissa with the growth parameters: L_∞=176.14 mm, W_∞=71.70 g, k=0.62, t₀=−0.27, φ=4.28, and t_i=1.53. The sex ratio (female/male) was 2.28﹕1, and the number of female individuals was significantly higher than that of male. The trend of gonadosomatic index and hepatosomatic index is opposite, indicating that the liver may provide energy for gonad development. It was speculated that the propagation period was from March to July. The absolute fecundity ranged from 1625 to 72882 eggs, with a mean of (20361±2601) eggs, and the relative fecundity ranged from 19 to 602 eggs/g, with a mean of (190±23) eggs/g. The distribution of egg diameter frequency was unimodal, which indicated it was one-time spawning fish. Compared with privious data, the fecundity of C. thrissa showed a decline tendency, so it is necessary to strengthen the protection and utilization of its resources.