Reproductive biology of the black goby, Gobius niger (Teleostei: Gobiidae), in the Gulf of Gabès (Tunisia, Central Mediterranean)

Abstract

The black goby Gobius niger (Linnaeus, 1758) (Gobiidae) is one of the most common gobies in southern Tunisian waters. This study provides the first detailed information on the reproductive biology of the G. niger in these areas. Samples of G. niger were collected by trawl from the Gulf of Gabès (Tunisia) between February 2009 and January 2010. A total of 1055 specimens were examined, ranging from 6.4 to 15.7 cm total length. The sex-ratio was in favour of males, especially in larger size-classes. The macroscopic analysis of the gonads and the progression of the monthly values of the gonadosomatic index (GSI) indicated that the reproductive season extended from March to June, with GSI peaking in May, and that spawning occurred from April to June. The utilization of lipid reserves, stored predominantly in the liver as well as in muscles, was important during the reproduction season. Monthly changes of the seminal vesicle somatic index showed that during the pre-spawning period they had a proliferation phase, followed by a regressive phase during the post-spawning period. Total fecundity of mature females ranged from 4280 to 14000 eggs per fish, showing a significant increase with size, with an average of 8522 ± 689 eggs per fish. The total length at 50% maturity was 10.13 ± 0.3 cm and 9.69 ± 0.18 cm for males and females, respectively.