Abstract
Reproductive biology of the strongspine silverbiddy, Gerres longirostris Lacepede, 1801, was studied by examining 1910 individuals collected fortnightly between May 2012 and January 2014 from the western Arabian Gulf, off Saudi Arabia. The samples were identified as 470 males, 1370 females and 70 undetermined. Maximum length observed was 30 and 40 cm (total length TL) for males and females, respectively. Overall sex ratio of males to females was found to be 1: 3.1. This sex ratio was significantly different from the normally expected 1: 1 ratio (p<0.05). Males constituted more than 50% of individuals measuring less than 20 cm but this male-bias was not significant (p>0.05). Females were significantly greater than males in all size classes between 20 and 34 cm with high significant difference (p<0.05) from the expected 1: 1 ratio between sexes. In length classes more than 34 cm, 100% of the fish were females. Size at first sexual maturity was estimated at 19.1 and 19.8 cm TL for females and males, respectively; all fish were mature at 20.7 cm TL. The spawning season coincided with late spring-early summer; gonadosomatic index (GSI) was highest (8.1-8.7 and 2.7-2.8 for females and males, respectively) in the peak season, May-June. GSI seems to peak in both sexes before 2-3 months of reaching the highest temperature. GSI and water temperature (T) were best expressed by a second-degree polynomial equation for both sexes, indicating that water temperature >30.28 degrees C might not be optimal for reproduction of G. longirostris.