Biological characteristics of rock goby, Gobius paganellus (Actinopterygii: Perciformes: Gobiidae), in the south-eastern Black Sea

Background. Gobius paganellus L. is one of the most common gobiid fish in the south-eastern Black Sea. The aim of present study is to provide information on age structure and growth, length at sexual maturity, annual cycle of gonad development, and diet of rock goby in the south-eastern Black Sea. Materials and methods. One hundred seventy-five specimens of G. paganellus were sampled from two stations in the province of Rize, south-eastern Black Sea. Samplings were performed by free diving using spear gun and hand net at night time. Specimens were dissected and sagittal otoliths, stomachs, livers, and gonads were removed. Otoliths were cleaned, immersed in glycerol, and examined on black background using reflected light at low magnification to determine age. Mean size at sexual maturity (L50) (i.e., size at which 50% of fish are mature) was estimated for males and females by fitting the logistic Gompertz function to the proportion of mature fish per cm size-class. The gonadosomatic index, seminal vesicle somatic index, and hepatosomatic index were calculated on monthly basis. The quantitative importance of different prey in the diet was assessed by calculating the frequency of occurrence, the percentage number, and the percentage mass of prey. The main food index (IMF) was calculated to combine the three used methods (IMF = (0.5 (%F + %N) %W)0.5). Results. The maximum age was estimated to be 7 and 6 years for males and females, respectively. The von Bertalanffy growth parameters was estimated from the mean age-length data for males and females (males: L∞ = 13.1 cm, k = 0.34, to= –0.11; females: L∞ = 18.2 cm, k = 0.18, to= –0.07). The estimated length at sexual maturity was 5.20 and 5.50 cm for males and females, respectively. The spawning season was between March and May. Total fecundity ranged from 1550 to 5839 eggs/female, with an average of 4322 ± 1109 eggs per female. The rock goby feeds on a wide variety of prey items, particularly on gammarids, brachyurans, natantians, bivalves, isopods, and fish. Conclusion. Growth rate (K) and growth performance index (φ’), length at sexual maturity, fecundity and feeding habits of Black Sea rock goby differ from Atlantic populations.