Reproductive biology and spawning aggregation fishing of the white-streaked grouper, Epinephelus ongus, associated with seasonal and lunar cycles

Abstract

The reproductive biology of the white-streaked grouper Epinephelus ongus, which forms spawning aggregations in the Yaeyama Islands, Okinawa, was examined by gonadal histology and oocyte development analysis. Gonadal histology showed that the spawning season was determined from April to July, but there are two spawning periods associated with the specific lunar cycle, during the week after the last quarter moon in two consecutive months. The pattern of oocyte development indicated that individual females spawned more than once, but fecundity may be determinate within a single spawning period. Fecundity was correlated to body size and ranged from several hundred thousand to a million eggs. Detailed catch data analysis showed that the catches during the two spawning months accounted for about 40 % of the annual landings and the fluctuation of the catch data corresponded well to some reproductive activities related to spawning aggregation. The two stepwise increases and the peaks of the catches coincided with the occurrence of matured individuals and the onset of spawning at the last quarter moon, respectively. These findings suggest that the spawning of E. ongus was concentrated within a few days just after the last quarter moon and that aggregation fishing was also concentrated in the critical reproductive periods.