FISHES OF THE GULF OF MAINE 229 



(spinous) dorsal is much shorter than the second (soft rayed) , if present (it may be 

 reduced to a series of very short spines or may be lost altogether in old age), and 

 that they either lack the dorsal and anal unlets so characteristic of the mackerel 

 tribe, or at most have but one of each. They differ further from the mackerels 

 in the number of vertebra? (only 22 to 23 as against upward of 30) , as well as 

 in the facts that the premaxillary bones are protractile (fixed in the mackerels) and 

 that the anal fin is preceded by two free spines that may either take the form of a 

 permanent finlet or may be lost in old age. Warm seas support a host of species 

 but none of them is more than an accidental stray to the Gulf of Maine. 



KEY TO GULF OF MAINE POMPANOS 



1. Body very much compressed, nearly or quite half as deep as long, or even deeper 2 



Body moderately stout, not more than one-third as deep as long 4 



2. Back and belly rounded; pectoral fin reaches not over two-thirds the way back toward 



the base of the caudal True pompanos (genus Trachinotus) 



Back and belly sharp edged; pectoral fin reaches at least halfway back toward the base 

 of the caudal 3 



3. Soft dorsal 84 and anal fins are low and taper evenly from front to rear Moonfish, p. 235 



The soft dorsal and the anal fins are both very high in front and taper abruptly toward 



the rear : Lookdown, p. 236 



4. There is only one well-developed dorsal fin (the soft rayed) , the first (spiny) dorsal be- 



ing reduced to a few short inconspicuous spines Pilotfish, p. 229 



There are two well-developed dorsal fins, though the second (soft) is much larger than 

 the first (spiny) 5 



5. There is a detached finlet behind the second dorsal fin, and one behind the anal fin 



Mackerel scad, p. 232 



There are no finlets behind the dorsal and anal fins 6 



6. There is a small finlet of two stout spines in front of the anal fin, and the latter is 



nearly as long as the second dorsal 7 



There is no finlet in front of anal fin (in young fry it is represented by two spines so 

 short they are apt to be overlooked) , and the anal is at least one-third shorter than 

 the second dorsal Rudderfish, p. 230 



7. Breast entirely scaly Hardtail, p. 234 



Breast naked except just in front of the ventral fins Crevalle, p. 233 



85. Pilotfish (Naucrates ductor Linnaeus) 

 Rudderfish; Shark pilot 

 Jordan and Evermann, 1S96-1900, p. 900. 



Description. — The pilotfish is stouter than the common mackerel (about one- 

 fourth as deep as long) — to take a familiar comparison — with blunter, rounded 

 nose, smaller mouth, and eye situated farther forward. Its long second dorsal 

 separates it from all the mackerel tribe, but its caudal peduncle is slender and 

 keeled on either side like that of a bonito. The first dorsal is reduced to four short 

 inconspicuous spines, which are connected by a membrane in young fish but this 

 is lost with growth. The second dorsal (26 or 27 soft rays) is slightly concave in 



91 tn the adult the first dorsal is reduced to a few short isolated spines, but in young fry some of these spines are elongated. 



