Ditty and Shaw Early life stages of Rachycentron canadum in northern Gulf of Mexico 



675 



(W.F. Hettler and L. Settle, pers. commun.), in coastal 

 waters 20-49 m deep (App. Table 1), and both near the 

 edge of the Florida Current and in the Gulf Stream 

 (Hassler and Rainville 1975, Eldridge et al. 1977). Off 

 North Carolina, cobia eggs are usually collected on 

 flood tides but few larvae are found in tidal inlets (W.F. 

 Hettler and L. Settle, pers. commun.). Cobia eggs and 

 larvae are usually collected in the upper meter of water 

 with surface-towed nets (Joseph et al. 1964, Hassler 

 and Rainville 1975 [implied], Eldridge et al. 1977; W.F. 

 Hettler, pers. commun.). Neither cobia study off the 

 Atlantic coast of the United States (Joseph et al. 1964, 

 Hassler and Rainville 1975) provides environmental 

 data, but eggs are successfully hatched at 19-35°/oo 

 (Hassler and Rainville 1975). 



Similarities in larval morphology provide evidence of 

 a sister-group relationship between cobia and dolphin- 

 fishes (Coryphaenidae) rather than that previously 

 hypothesized between cobia and remoras (Echeneidi- 

 dae) (Johnson 1984). Larvae of both cobia and the 

 dolphinfishes share similar patterns of head spina- 

 tion: laterally swollen pterotics; a single, simple spine 

 on the supraorbital ridge of each frontal bone (except 

 in pompano dolphin C. equiselis, which may have 

 multiple spines along the ridge; JGD, pers. observ.); 

 a small posttemporal spine; and several spines along 

 the anterior and posterior preopercule, including an 

 enlarged spine on either side of the angle. However, 

 cobia have a small supracleithral spine (Dawson 1971, 

 this study) that dolphinfishes lack. Remoras complete- 

 ly lack head spines. Both cobia and the dolphinfishes 

 have epithelial spicules, a specialization unique to lar- 

 vae of these species (Johnson 1984). We found spicules 

 visible on the integument of both cobia and the dolphin- 

 fishes by 4mm (JGD, pers. observ.) and they cover the 

 entire body surface, except the pupil of the eye. Spicule 

 composition and function, however, are unknown 

 (Johnson 1984). Larval cobia are further separated 

 from superficially similar remoras by the presence of 

 large hook-like teeth on the dentary in remoras. Cobia 

 lack these teeth. Larval cobia differ from the dolphin- 

 fishes by the lack of dorsal and anal spines and a higher 

 vertebral count in the dolphinfishes (25 in cobia vs. 

 30-34 in dolphinfishes). Dolphinfishes also usually have 

 50-1- soft dorsal rays, whereas cobia have 27-33. 



Acknowledgments 



This study was supported by the Marine Fisheries Ini- 

 tiative (MARFIN) Program (contract nos. NA90AA- 

 H-MFlll and NA90AA-H-MF727). Thanks to those 

 who loaned us specimens or provided data: Karen 

 Burns, Mote Marine Lab, Sarasota FL; John Caruso, 

 Tulane University Museum, New Orleans LA; L. Alan 



Collins and Churchill Grimes, NMFS Southeast Fish- 

 eries Science Center, Panama City FL; Wayne Forman 

 and Leroy Kennair, Freeport-McMoRan, New Orleans 

 LA; Bruce Comyns and Stuart Poss, Gulf Coast Re- 

 search Lab, Ocean Springs MS; Peter Berrien, NMFS 

 Northeast Fisheries Science Center, Sandy Hook NJ; 

 Bill Hettler and Larry Settle, NMFS" Southeast 

 Fisheries Science Center, Beaufort NC; and Karsten 

 Hartel, Museum of Comparative Zoology at Harvard. 

 Thanks also to the Southeast Area Monitoring and 

 Assessment Program (SEAMAP) and the Gulf States 

 Marine Fisheries Commission for providing specimens 

 and environmental data; to the Marine Resources, 

 Monitoring, Assessment and Prediction (MARMAP) 

 program for providing eggs collected during ichthyo- 

 plankton surveys; to Cathy Grouchy for illustrating 

 the egg and larvae; and to Joe Cope for computer 

 assistance. 



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