Reproductive biology of the lesser African threadfin Galeoides decadactylus in Gabon, Gulf of Guinea

Abstract

The lesser African threadfin Galeoides decadactylus (family Polynemidae) is one of the most captured marine fish species in Central Africa. This study examines aspects of the reproductive biology of G. decadactylus in the Libreville area of Gabon. Fish caught with encircling gillnets and bottom gillnets were collected from May 2017 to May 2018 from artisanal fishermen. A total of 776 specimens were studied, comprising 401 females (14–36 cm total length [TL]), 347 males (13–28 cm TL), and 28 individuals of indeterminate sex (12–16 cm TL). Monthly monitoring of gonadosomatic ratio, condition factor and sexual maturity stages revealed that G. decadactylus reproduces continuously but has two slight peak periods: one in the long rainy season and the other in the short rainy season. The species is protandrous, with sizes at first sexual maturity of 17.7 cm TL for males and 18.7 cm for females. Mature individuals largely dominated the catches of small-scale fishers in Gabon. Mean absolute fecundity of females was 179 447 (SD 107 240) oocytes, and mean relative fecundity was 848 (SD 323) oocytes g–1. This study provides fisheries managers with crucial knowledge, such as size at sexual maturity, that could be used as a basis for sustainable management of G. decadactylus stocks in Gabon using minimum size limits.