Reproductive biology of cobia, Rachycentron canadum, from coastal waters of the southern United States

Reproductive biology of the cobia, Rachycentron canadum, is described from four coastal areas in the southern United States. Samples were obtained fro m recreational fishermen between December 1995 and November 1997 from the s outheastern United States (Morehead City, NC, to Cape Canaveral, FL), the e astern Gulf of Mexico (Ft. Myers to Crystal River, FL), the north-central G ulf of Mexico (Destin, FL, to Chandeleur Islands, LA) and the western Gulf of Mexico (Port Aransas, TX). Histological evidence of spawning occurred fr om April through September in all areas. Some female cobia (17-32%) through out the Gulf of Mexico had spent or regressed ovaries by July. Gonadosomati c index peaked between May and July throughout the region. Ovaries of femal es from all areas contained both postovulatory follicles (POF) and oocytes in final oocyte maturation (FOM) during all months of the reproductive seas on. Batch fecundity was calculated by using three different methods: oocyte s >700 pm were fixed in 1) Gilson's fixative or 2) 10% neutral buffered for malin (NBF), and 3)oocytes undergoing FOM were sectioned for histological e xamination. Mean batch fecundity ranged from 377,000 +/- 64,500 to 1,980,50 0 +/- 1,598,500 eggs; there was no significant difference among methods. Ba tch fecundity calculated with the NBF method showed a positive relationship with fork length (P=0.021, r(2)=0.132) and ovary-free body weight (OFBW; P =0.016, r(2)=0.143). Relative batch fecundity was not significantly differe nt among months during the spawning season and averaged 53.1 +/-9.4 eggs/g OFBW for the NBF method and 29.1 +/- 4.8 eggs/g OFBW for the FOM method. Al though spawning frequencies were not significantly differ ent among areas ( P=0.07), cobia from the southeastern United States and north-central Gulf o f Mexico were estimated to spawn once every 5 days, whereas cobia from the western Gulf of Mexico were estimated to spawn once every 9 to 12 days.