Biology of Reproduction and Histological Examination of Female Egyptian Sole, Solea aegyptiaca (Chabanand, 1927) from Wadi El-Rayan Lake, El-Fayoum, Egypt

The present study examined the reproductive biology and histological characteristics of Solea aegyptiaca in the Lower Lake of Wadi El-Rayan, El-Fayoum, Egypt. The investigation aimed to estimate biological features such as the maturity stages throughout the spawning season, gonadosomatic index (GSI), fecundity, egg diameter, and spawning, as well as histological characteristics of the ovaries, including the previtellogenesis and vitellogenesis phases. Monthly fish samples were collected from the 3rd depression of Wadi El-Rayan Lake from October 2022 to September 2023. This study revealed that the spawning period of Solea aegyptiaca extended from late December to early March. The peak GSI value in females was recorded at 10.6 in January, while the minimum value was 1.2 in August. In males, the highest GSI value was 0.17 in late December, with the lowest value recorded at 0.042 in September. The frequency distribution of egg diameters consisted of 10 groups. The first four groups represented small and transparent oocytes (previtellogenesis phase), while the second group consisted of yolky oocytes (vitellogenesis phase). In addition, a strong relationship was recorded between the absolute fecundity of fish and their length and weight. For the absolute fecundity, a range from 33,635 to 90,520 was detected in egg production, corresponding to fish weights of 55.5 and 180 grams, respectively. Furthermore, relative fecundity was directly proportional to fish length, with egg production varying from 1,367 to 2,695.25 eggs per centimeter for fish measuring between 19 and 27 cm. Similarly, relative fecundity was directly proportional to fish weight, ranging from 440 to 650 eggs per gram of gutted weight for fish between 55.5 and 180 grams. Oogenesis was divided into the previtellogenesis and vitellogenesis phases, with sub-stages including immaturation, maturation, vacuolization, yolk deposition, ripening, and spawning. Our findings suggest that Solea aegyptiaca has an extended spawning period with fractional spawning.