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.

Solea aegyptiaca (Chabanaud, 1927) is one of the most common Soleid species in southern Tunisian waters. This study provides the first detailed information on the reproduction biology of S. aegyptiaca in these areas. Samples of S. aegyptiaca were collected by trawl from the Gulf of Gabes (Tunisia) between April 2013 and March 2015. A total of 1638 specimens were examined, ranging from 9.7 to 30.7 cm total length. The sex ratio was in favour of males in smaller size classes and females 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 October to February, with GSI peaking in November and December for males and females respectively, and that spawning occurs once a year from November to February. The utilization of lipid reserves, stored predominantly in the liver as well as in muscles, was depicted. The estimated average length at first maturity was 22.31 ± 0.41 cm for males and 23.19 ± 0.184 cm for females. Total fecundity of mature females ranged from 14,160–62,700 eggs per fish, showing a significant increase with size, with an average of 33,020 ± 5239 eggs per fish.

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.