First Report on the Reproductive Biology of the Redtail Scad Decapterus kurroides Bleeker, 1855 in Iligan Bay, Southern Philippines

This study provided the first report on the reproductive biology of the redtail scad, Decapterus kurroides. The reproductive activity of the redtail scad was assessed to characterize its sex ratio, spawning period, length at maturity, and fecundity. Meanwhile, remote sensing data on environmental variables were accessed from Giovanni online data system. Fish samples were collected monthly from October 2017 to September 2018 from both commercial and municipal landed catches. Male D. kurroides was found to have a larger size than the female in terms of mean total length and mean body weight, but it did not differ significantly from the female (t = 1.31, df = 1,348, p = 0.19). Collected male and female samples were mostly in the 15.1 – 18.0 cm size class. Overall sex ratio exhibited female dominance (1.2:1), which significantly deviated from the 1:1 ratio (x2 = 8.17, p = <0.05). As expected for tropical fish, spawning of D. kurroides occurred year-round, with peak spawning in December and minor spawning events in March and August, as reflected in the monthly percent occurrence of different gonad maturity stages and gonadosomatic index evolution. Among the environmental variables evaluated, sea surface temperature appeared to have more influence on the spawning of D. kurroides followed by chlorophyll-a concentration. Females matured at a length of 17.2 cm, while males matured at a length of 17.6 cm. Absolute fecundity ranged from 6,416 to 197,672 eggs per female with a mean of 61,733 ± 3,955 and increased proportionally with gonad weight. Information from this study may be used to formulate effective management strategies for the resource.