Reproductive biology of the rock goby, Gobius paganellus (Actinopterygii: Perciformes: Gobiidae), on the southern Tunisian coast (Gulf of Gabes)

Abstract

The rock goby Gobius paganellus is one of the most common gobiid fish on the southern Tunisian coast and this study provides the first detailed information on its reproductive biology in the Gulf of Gabes. A total of 356 males (8.9–14 cm total length, TL) and 273 females (9.1–14.3 cm TL) were analyzed. Specimens were dissected and their gonads and livers were removed. Mean size at sexual maturity (TL₅₀; i.e., length at which 50% of the fish are mature) was estimated for males and females by fitting the logistic Gompertz function to the proportion of mature fish per centimeter size class. The gonadosomatic index, the seminal vesicle-somatic index (SVSI), the hepatosomatic index, and the condition index were calculated on a monthly basis. In the entire population, the sex ratio was unbalanced, males dominating among larger size classes. The reproductive period started in October and lasted until March, and the spawning season was between January and March. Monthly changes in the SVSI showed that during the pre-spawning period they have a proliferation phase, followed by a regressive phase during the post-spawning period. The use of lipid reserves, stored predominantly in the liver as well as in muscles, was important during the reproductive season. The estimated length at sexual maturity was 11.44 ± 0.25 cm for males and 10.37 ± 0.23 cm for females. Total fecundity ranged from 5280 to 14,320 eggs per fish, with an average of 8565 ± 608 eggs per fish.