372 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



4. Second dorsal and anal fins are conspicuously falcate in shape, very high in front, tapering abruptly toward the rear; 



there are no enlarged bony plates along the lateral line on the caudal peduncle Lookdown, p. 379 



Second dorsal and anal fins only moderately high in front, tapering rearward gradually; caudal peduncle with weak 

 bony plates along the lateral line 5 



5. Upper anterior profile of head concave; ventral fins very small; anterior rays of soft dorsal and of anal not elon- 



gate Moonfish, p. 378 



Upper anterior profile of head convex; ventral fins as long as head or longer; anterior rays of soft dorsal and anal 

 fins elongate, threadlike Thread fin (probably the young of the Cuban jack) , p. 381 



6. There is only one well-developed dorsal fin (the soft rayed), the first (spiny) dorsal being reduced to a few short 



spines, without separate fin membranes Pilot fish, p. 372 



There are two well-developed dorsal fins though the first (spiny) is smaller than the second 7 



7. There is a detached finlet behind the dorsal fin and one behind the anal fin Mackerel scad, p. 374 



There are no finlets behind the dorsal and anal fins 8 



8. There is no finlet in front of the anal fin; and the anal is only about one-half as long as the soft 



dorsal Rudderfish, p. 373 



There is a finlet of 2 short spines in front of the anal fin, and the anal fin is nearly or quite as long 

 as the soft dorsal 9 



9. The forward part of the lateral line is scarcely arched Goggle-eyed scad, p. 377 



The forward part of the lateral line is strongly arched 10 



10. The breast is naked, except for a small patch of scales in front of the ventral fins Crevalle, p. 375 



The breast is covered with scales 11 



11. The body (to base of tail) is not more than 3 times as long as it is deep; the soft dorsal fin has only 



23 to 25 rays Hardtail, p. 376 



The body to base of tail is more than 3 times as long as it is deep; the soft dorsal fin has 30 to 35 

 rays __ Saurel, p. 377 



Pilotfish Naucrates ductor (Linnaeus) 1758 



Rudderfish; Shark pilot 



Jordan and Evermann, 1896-1900, p. 900. 



Description. — The pilotfish is one of the more 

 slender carangids (body about one-fourth as deep 

 as it is long), round-sided, about two-thirds as 

 thick as it is deep, and somewhat mackerel-like 

 in appearance though with a blunter, more rounded 

 nose and smaller mouth, while its caudal peduncle 

 is conspicuously keeled on either side like that of 

 a bonito. But its long second dorsal fin separates 

 it from all the mackerel tribe. The first dorsal 



fin is reduced to three or four short inconspicuous 

 spines, which are connected by a membrane in 

 young fish but this membrane is lost with growth. 

 The second dorsal (26 or 27 soft rays) is weakly 

 concave in outline and originates midway between 

 tip of snout and base of caudal fin. The anal fin 

 is similar to the second dorsal in form, but is oidy 

 about half as long (16 or 17 raj's), and is preceded 

 by two very short spines. It resembles the rud- 

 derfish in this but the first dorsal of the latter is 

 well developed and has 7 spines instead of only 3 

 or 4. The ventrals, situated far forward under 

 the pectorals, are about as large as the latter. The 

 caudal is large and deeply forked. The edge of 



^mm 



*S?r? : - 



'•$ 



Figure 197. — Pilotfish (Naucrales ductor), about 13 inches long, New Bedford, Mass. After Goode. Drawing by 



H. L. Todd. 



