Determination of the reproductive biology of horse mackerel (Trachurus mediterraneus, Steindachner, 1868) by histological method in the Eastern Black Sea

In this study, it was aimed to determine the reproductive strategy and period of the horse mackerel (Trachurus mediterraneus, Steindachner, 1868) fish stocks in the Eastern Black Sea by empirical and histological (microscopic, macroscopic) methods. The length, weight, sex composition, age, reproductive characteristics, GSI, HSI, CF, gonad development stages, egg diameters, batch and relative egg productivity (fecundity) and first maturity length (LM50) of horse mackerel were investigated. 1533 horse mackerel fish collected in a 12-month period between September 2019 and August 2020 were sampled, lengths of samples varies between 8.5 cm and 18.4 cm, mean length and weight were calculated as 11.87±1.323 cm and 14.06±5.468 g, respectively. It was determined that all individuals consisted of 770 females (50.23%) and 763 males (49.77%) individuals. Age distribution was found to be between 0-IV years and the most intense age group was 1 year. The month with the highest GSI value in both female and male individuals was determined as June (D=4.68±1.991, M=3.55±1.533). Batch fecundity was estimated as 3437.14±4459.46 eggs/individual and batch relative fecundity as 124.03±100.27 eggs/g. While the average of the hydrated egg diameters was 732.71±153.72 µm, the average of the total egg diameters was determined as 414.86±98.66 µm. The first sexual maturity length (LM50) was calculated as 11.11 cm for females and 10.86 cm for males. According to the results obtained in this study, it was concluded that the spawning period of horse mackerel occurred between may and august as a result of both empirical and histological methods, and the spawning strategy was partial and asynchronous. Keywords: Trachurus mediterraneus, Reproduction, Fecundity, Gonad Histology, Eastern Black Sea