Determining Sexual Development and Size at Sexual Maturity of Sardinella tawilis and its Implications on Management

Abstract

Reproductive biology is important in formulating management interventions for fish stocks. Limits on catch size are established based on the identified size at first sexual maturity of the target fish species, which can be accurately determined through histological analysis of gonads. The study investigated the reproductive characteristics of the endangered Sardinella tawilis and determined the size at first sexual maturity based on histological analysis. Between 2017 and 2018, 312 fish samples with different lengths were collected in Taal Lake's northern and southern basins. The length-weight relationship of S. tawilis shows that the species exhibits negative allometric growth. Female S. tawilis, characterized by larger sizes, are significantly more abundant in our catches than male individuals (mean sex ratio p<0.05) and exhibit an asynchronous oocyte development. Histological analysis of gonads showed that the size at sexual maturity for both male and female S. tawilis were at 75 to 79 mm FL, which was smaller than the reported size at sexual maturity based on morphological analysis. Smaller average and maximum lengths, as well as the size at first sexual maturity, could suggest that S. tawilis has experienced growth overfishing and a slowly degrading lake environment through time. Results highlighted the importance of ensuring that immature S. tawilis can enter sexual maturity and contribute to the population through reproduction. It is also highly recommended that the size of S. tawilis to be targeted by fisheries are individuals above 100 mm FL, which exhibited the highest proportion of spawning capable individuals.