Phenotypic plasticity in life-history characteristics of the invasive redbelly tilapia (Coptodon zillii) in Shuikou Reservoir, Minjiang River, China

In recent decades, the redbelly tilapia ( Coptodon zillii ) has become one of the most serious invasive alien fish species worldwide. The successful invasion of this fish may largely depend on the plasticity of its life-history traits. In order to explore the life-history traits of the invasive population of C. zillii , we chose Shuikou Reservoir of Minjiang River, China, as a typical invasive habitat, and 1,041 specimens were collected monthly from March 2023 to February 2024. Life-history traits were systematically investigated. The results showed that the entire population consists of individuals from age 1 to age 6, with the highest percentage (95.10%) of younger individuals at 1–2 years old. The sex ratio of males to females was 1.05:1. The equation of the length-weight relationship was W = 0.048* L 2.938 , and the parameters of von Bertalanffy growth equation were L ∞ = 32.937 cm, W ∞ = 1381.010 g, k = 0.131, and t 0 = -2.056. The breeding season ranged from March to November, and the minimum sexually mature standard lengths of females and males were 8.7 and 9.0 cm, respectively. Mean absolute fecundity was 3854.38±254.43 eggs, while mean relative fecundity to standard length and body weight were 301.95±16.94 eggs/cm and 60.44±3.56 eggs/g, respectively. These results indicated that the population of C. zillii in Shuikou Reservoir presented characteristics such as a high proportion of young individuals, low growth rate, long spawning season, high fecundity, and smaller size at first maturity compared with the native and other invasive populations. Both opportunistic and equilibrium life-history strategies might have contributed to their successful invasion, and there is a potential risk of further population expansion.