Macroscopic gonad staging and reproductive seasonality in the Gorean snapper, Lutjanus goreensis a gonochoristic West African Lutjanid
In Nigeria, the Gorean snapper Lutjanus goreensis is an important component of artisanal fisheries and trawl landings although substantial gap exists on some aspects of the species’ reproductive biology in the entire Gulf of Guinea. The main objective of the study was to characterize the sexual differentiation and ratio, spawning seasonality and pattern through observation of three somatic indices: gonadosomatic index IG, hepatosomatic index IH and the Relative Condition Factor (Krel), macroscopic staging and size at first sexual maturity of the species. Spawning seasonality and pattern were best determined from temporal trends of IG and macroscopic gonad stage frequencies. The fish is monogamous with sex ratio of 1 male: 1 female. Five distinct gonad maturity stages and lack of population synchrony in gonadal development were distinguished. Mean sizes at first sexual maturity were 34.61cm TL and 34.21 cm TL for females and males, respectively. Multiple spawning peaks reflected by high IG occurred in December, May to June and August indicated protracted spawning while lowest IG occurred in March-April, denoted a resting phase. The species is a multiple spawner as evinced from asynchronous development of the gonads. It showed continuous reproduction throughout the year, particularly at higher intensity during the heavy rains (May to September). While these findings imply continuous recruitment into fishery, it is recommended that for optimal exploitation, minimum capture size has to be increased above sizes at sexual maturity.