Reproductive biology of wahoo (Acanthocybium solandri) in the waters off eastern Taiwan

Length and weight data and gonads of 482 (223 female and 259 male) specimens of wahoo (Acanthocybium solandri) caught by the eastern Taiwanese offshore longline and troll fisheries were collected at Shinkang Fish Market from December 2005 to December 2008. Size of the specimens ranged from 47.5 to 148.4 cm FL (fork length) or 0.6 to 27.0 kg RW (round weight). Chi-square tests found a generally homogenous sex ratio of 1:1 among months and 5-cm length intervals, except for the months of August 2006, June 2007 and June 2008, and the length interval of 105.0-109.9 cm. The overall sex ratio was not different from 1:1. Monthly variations in gonadosomatic index, mean diameters of oocytes, and histological examination provided the basis to define the stages of gonadal development. The results showed that spawning season was from Match to August with a peak between April to July. The predicted length at 50％ maturity was 98.9 cm for females and 85.8 cm for males, and smallest size of maturity was 86.3 cm for females and 71.3 cm for males. On the basis of the proportion of females with postovulatory follicles, spawning frequency was estimated at 6.00 days for mature females and 2.80 days for mature and reproductively active females, implying that reproductively active wahoo spawned almost every three days. On the basis of the proportion of males with spermatozoa and the feature of sperm duct, spent frequency was estimated at 2.70 days, implying that reproductively active wahoo spawned almost every three days. The average batch fecundity was 81.3 ± 8.4 (S.E.) ten thousand oocytes, or the average relative fecundity was 123.8 ± 9.2 (S.E.) oocytes per gram of body weight. Relationship between batch fecundity and fork length, round weight, or gonad weirgt was , , and , respectively, indicating that batch fecundity would increase with fork length, round weight and gonad weight.