Reproductive pattern and length at first sexual maturity of the whiting (Merlangius merlangus, Nordmann, 1840) in the Black Sea

Samples of whiting (M. merlangus) (n = 1545) were collected using bottom trawl in the southern Black Sea during 2017–2018 and were subjected to reproductive biology assessments. These assessments included the gonadosomatic index, macroscopic and microscopic gonad phases, oocyte diameter distributions, batch fecundity, microscopic analysis of oocytes, and histology. The assessment results revealed a significant difference in sex ratio the samples (female: 877, male: 668). Analyses of the gonadosomatic index (GSI), along with macroscopic and microscopic phase evaluations, indicated that the most intense reproductive periods occurred in May and November, with two peaks observed during the studied year. Examination of oocyte structures and diameter distributions in histological sections taken from the ovaries each month showed that the whiting in the southern Black Sea exhibited multi-spawning behavior and had determinate fecundity. Additionally, the monthly batch fecundity (FB) and relative batch fecundity (FBR) of spawning whiting were calculated throughout the year. The average FB was 17823 ± 21,353 hydrated oocytes, while the FBR was 243 ± 143 hydrated eggs per gram. The length at first maturity for males and females were 12.80 cm and 13.72 cm, respectively. In light of the study's results, it is recommended to develop a new fisheries management strategy aimed at contributing to the sustainability of whiting stocks in the Black sea. This strategy should consider the most efficient spawning periods identified in this study, as well as other reproductive strategies, and focus on preserving larger individuals that can enhance egg production within the stocks.