Does the fishing pressure induce fish to mature early? An evaluation of the reproductive biology of Nemipterus japonicus (Bloch, 1791) from the Malabar Coast of India

Abstract In fisheries management, a comprehensive comprehension of the reproductive biology of fish species is imperative, with specific emphasis on factors such as sexual maturation, the dynamics of the reproductive cycle, and the quantitative assessment of fecundity. To elucidate the reproductive dynamics of Nemipterus japonicus captured along the Malabar coast, encompassing parameters such as the sex ratio, sexual maturation, fecundity, and reproductive periodicity, a rigorous investigation was conducted spanning the period from 2017 to 2021. Sampled individuals of N. japonicus exhibited total lengths ranging from 5.5 to 35.2 cm. The exponent value (b = 2.991) observed in this current study exhibited a high degree of proximity to 3, indicative of an isometric growth pattern. The collective sex ratio stood at 1:1.3, signifying a higher prevalence of females than males. Attainment of 50% sexual maturation (Lm50) occurred at a total length of 15 cm for males and 15.5 cm for females which is earlier than the reported length. Monthly changes in the gonadosomatic index exhibited elevated values from September to December, reaching their zenith in October. The study ascertained N. japonicus matured significantly earlier than in the last decade and the spawning season shifted to lower temperature months for better reproductive output along the south-west coast of India.