Reproductive parameters of the chub mackerel, Scomber japonicus (Houttuyn, 1782) from the East Mediterranean Sea, Egypt

This study aimed to explore the reproductive biology and histology of Scomber japonicus from the Mediterranean Sea, Egypt. For this purpose, a total of 511 specimens were collected monthly from Alexandria landing site from the catches of purse-seine nets during 2017-2018. Throughout the reproductive cycle, four maturity stages were determined for males and females (Immature (I); Maturing (II); Ripe and spawning (III), and Spent stage (IV)). Females were predominant the sex ratio (1 Male: 1.19 Female). The maturity stages with Gonado-somatic Index (GSI) and ova diameter, illustrating the fractional spawning mode of S. japonicus with an extended spawning (March-June) and a maximum GSI peak in April-May for both sexes. Likewise, Female Hepato-somatic index (HIS) exhibited significant rise during spawning time. The mean absolute fecundity was 28762.98±15431.04 oocytes per ovary showing positive correlations with both total weight (0.974) and total length (0.95). The relative fecundity ranged from 420 to 2553 egg/cm for length (TL), and from 76 to 379 egg/g for total weight, showing significant correlation with total length (0.906), and insignificance with total weight (0.398). The length at maturity was 19.7cm and 19.5cm for males and females, respectively. The histological investigations confirmed the spawning time via yolky stages with a partial mode of asynchronous oocytes. These data are updated and provided insights about the reproductive strategy of S. japonicus and its future fishery management in the area.