Reproductive traits of the obtuse barracuda Sphyraena obtusata Cuvier, 1829 in the Gulf of Mannar, south-east coast of India

The reproductive biology (sex ratio, maturity and fecundity) of the obtuse barracuda Sphyraena obtusata Cuvier, 1829 was investigated based on 698 specimens (323 females and 375 males) sampled along the Pamban Coast in the Gulf of Mannar during the years 2018 and 2019. The total length of the samples ranged from 11.8 to 41.6 cm and the overall sex ratio (male:female) was 1:0.86. The length at first maturity (Lm(50)) was estimated to be 31.26 cm for females and 31.12 cm for males. Monthly changes in the gonadosomatic index (GSI) values and reproductive phases revealed a protracted spawning, extending from September to February with a peak in January. However, the presence of mature females throughout the year indicated year-round spawning behaviour of the species in the region. Detailed histological studies of the ovary further confirmed that the species is a continuous batch spawner. The estimated absolute batch fecundity ranged between 20,520 and 2,22,422 oocytes and the relative batch fecundity ranged from 261 to 754, with an average of 505 ova per gram body weight of fish. The ova size ranged from 0.03 to 0.84 mm (Mean +/- SE: 0.43 +/- 0.04). Fecundity positively correlated with the total length and total weight of the fish, indicating larger females produced a greater number of ova compared to the smaller ones.