Reproductive biology of the Bloch's gizzard shad, Nematalosa nasus (Teleostei: Clupeiformes) in the coastal waters of the Persian Gulf

This study was conducted to determine the reproductive biology of Nematalosa nasus for a period of 18 months from September 2016 to April 2018 in the coastal waters of the Persian Gulf. In total, 618 specimens (331 males and 287 females) were collected as bycatch in the shrimp bottom trawl net. Fork length ranges from 95-160mm (mean 135±0.7mm) and 95 to 169mm (mean 139±0.8mm) in males and females, respectively. The overall sex ratio showed that the males were dominating (1.15:1). Also, the size-specific sex ratio showed that the number of males was more dominant in fork length classes less than 135mm, and females generally dominated at lengths greater than 150 mm. Monthly variations in the Gonad Somatic Index (GSI) and morphological maturity stages of ovary indicated that Bloch's gizzard shad had a long spawning season with two distinct peaks in autumn and winter (from September to February). The smallest females mature Bloch's gizzard shad were found in the size classes 120-124mm of fork length and the Lm50% was estimated at 150mm.