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Fishery Bulletin 92(2), 1994 



Table 5 



Characters helpful in separating larvae of common dolphin (Coryphaena hippurus) from pompano dolphin 

 (C. equiselis). 



' At <4.0^1.5 mm SL. 



2 At about 8.0 mm SL. 



3 Laterally on body and median fins. 



postflexion (Figs. 1 and 2). In general, our findings 

 agree with those of Aoki and Ueyanagi (1989). Lack 

 of pelvic-fin pigment in pompano dolphin is diagnos- 

 tic for separating the two species when common 

 dolphin lose lateral banding through preservation or 

 specimen deterioration. Although the 8.5-mm com- 

 mon dolphin larva illustrated in Johnson (1984) 

 lacks pelvic pigment, this specimen has bands of 

 pigment laterally on both the body and median fins. 



Number of myomeres and dorsal-fin rays separate 

 juvenile and adult common dolphin from pompano 

 dolphin (30 or 31 vertebrae and 58-66 [x=61] dor- 

 sal rays in common dolphin; 33 or 34 vertebrae and 

 52-59 [x=55] dorsal rays in pompano dolphin; 

 Collette et al., 1969; Potthoff, 1980). Great care must 

 be taken when counting the most anterior dorsal- 

 fin elements (Gibbs and Collette, 1959), however, be- 

 cause anterior dorsal rays are short and develop late 

 (Potthoff, 1980). Myomeres are difficult to count 

 without clearing and staining larvae because 

 dolphinfish are heavily pigmented. 



Early larval development of common dolphin and 

 pompano dolphin from the Gulf is similar to that in 

 the western Pacific Ocean (Aoki and Ueyanagi, 1989). 

 Developmental milestones (e.g. initial formation of 

 dorsal- and anal-fin bases, yolk-sac absorption, and 

 lateral body banding) occur at similar sizes in common 

 dolphin from both the Gulf and western Pacific Ocean. 

 We found yolk-sac absorption in common dolphin com- 

 plete by about 3.7 mm, as did Aoki and Ueyanagi 

 (1989). Off Japan, however, common dolphin do not 

 complete yolk-sac absorption until about 6 mm TL 

 (Okiyama, 1988). Aoki and Ueyanagi (1989) did not 

 discuss either maxillary or posttemporal spines or the 

 epithelial spicules noted during this study. 



Morphometries are generally greater in pompano 

 dolphin than in common dolphin from the gulf by 

 early postflexion (Table 1). Differences in mean mor- 

 phometric ratios (expressed as % SL) between spe- 

 cies from the Pacific Ocean are significant (Student's 



£-test, a=0.05) for larvae 5-10 mm; relative growth 

 of all body parts measured (except preanal length) 

 were greater in pompano dolphin than in common 

 dolphin (Aoki and Ueyanagi, 1989). 



Distribution of dolphinfish larvae (Table 2, Fig. 3), 

 juveniles, and adults is apparently limited by the 

 20°C isotherm (Gibbs and Collette, 1959). We found 

 larval dolphinfish of both species primarily at tem- 

 peratures >24°C and salinities >33 ppt, as did Fahay 

 (1975), Powles (1981), and Aoki and Ueyanagi 

 ( 1989). On the basis of water temperatures between 

 25 and 30°C (those when common dolphin larvae 

 primarily occur), we estimate a common dolphin egg 

 would hatch between 26 and 38 hours. Incubation 

 time at 25°C predicted for common dolphin eggs 

 from the Gulf was similar to that of Hagood and 

 Rothwell 1 at 26°C, but less than incubation times 

 predicted by other studies (Table 3). 



Location of dolphinfish spawning is poorly docu- 

 mented. We believe that spawning occurs in oceanic 

 waters based on the collection of preflexion larvae 

 of both species at stations primarily beyond the con- 

 tinental shelf (Appendix Fig. 3). In addition, >80% 

 of larvae of each species (Fig. 3) and 85% of stations 

 where larvae occurred were over or beyond the outer 

 continental shelf (Appendix Fig. 2). These findings 

 support information from along the Atlantic coast of 

 the southeastern U. S. that dolphinfish larvae are 

 most abundant near or beyond the 180 m depth 

 contour (Powles, 1981). In the Gulf, larvae of both 

 common and pompano dolphin were collected over 

 a similar median (Table 2), mean, and range of sta- 

 tion depths (mean: 815 m for common dolphin and 

 782 m for pompano dolphin based on our weighted 

 method of calculating these statistics). This similar- 

 ity between species in distribution of larvae is rein- 

 forced by the average depth of stations where lar- 

 vae were captured. Average station depth of capture 

 was 1198 m for common dolphin (n=216 stations) 

 and 1042 m for pompano dolphin (n=64 stations). 



