FISHES OF THE GULF OF MAINE 



149 



HATCHET FISHES. FAMILY STERNOPTYCHIDAE 



These are deep, thin, flat-sided little fishes, with 

 various spiny projections, large oblique mouths 

 with small teeth, large eyes which are directed up- 

 wards in some of them but sidewise in others, and 

 ventral fins placed far back. Some of them have 

 an adipose fin behind the rayed dorsal, but others 

 do not. All of them are silvery, and all of them 

 have series of large and conspicuous luminescent 

 organs on the lower part of the body. They are 

 to be found in the mid-depths in all oceans, some- 

 times in great abundance. 



Silver hatchetfish Argyropelecus aculeatus 

 Cuvier and Valenciennes 1849 



Jordan and Evermann, 1896-1900, p. 604, as A. olfersi 

 Cuvier, 1829. 



Figure 68. — Silver hatchetfish (Argyropelecus aculeatus). 

 After Brauer. 



Description.- — This little fish is of so bizarre an 

 appearance that once seen it could hardly be mis- 

 taken for any other species yet known from our 

 Gulf, or for any that is likely to stray thither, 

 unless one of its own tribe. 49 Its body is very 

 thin sidewise, with its forward part a little less 

 than three-fourths (70 percent) as deep as it is 

 long from snout to base of tail fin, but with the 

 ventral contour bending upward abruptly about 

 midway of its length in characteristic contour, so 

 that the rear half is much less deep than the for- 

 ward half. This break in the ventral contour is 

 marked by two short bony spurs, which are out- 



*• The several known species of Argyropelecus resemble one another so 

 closely that their Identification calls for a specialist. They have been re- 

 viewed by Schultz, Proc. U. 8. Nat. Mus., vol. 86, 1938, pp. 147-153. The 

 most detailed description of this particular hatchetfish, with the best Illus- 

 tration (copied here as fig. 68) Is by Brauer, Wlss. Ergeb. Deutschen Valdicta 

 Tlefsee-Exped., vol. 18, Pt. 1, 1908, p. 110, fig. 47. 



growths from the pubic bones, and there is a short 

 single spur (outgrowth from the pectoral arch) in 

 front of them in the mid ventral line. 



The eyes are large, so high up that the space 

 between them on the top of the head is very 

 narrow, and they are directed more upward than 

 sidewise. The mouth is noticeably large, with 

 wide gape, and it is so strongly oblique that the 

 upper jaw is nearly vertical. 50 The tips of the two 

 jaws are about even one with the other when the 

 mouth is closed, and both jaws are armed with a 

 large number of tiny sharp teeth. The dorsal fin 

 is short, about midway of the fish, and of two 

 parts, separated by a deep but short notch. The 

 forward subdivision is in the form of a hard, 

 triangular plate (apex rearward) supported by 8 

 or 9 hard spines, the rearmost of which is the 

 stoutest and longest. The rearward subdivision 

 is supported by 9 soft rays, that are bifid toward 

 their tips. The adipose fin is long and low. The 

 pectorals are as long as about two-fifths the 

 greatest height of the body. The ventral fins, 

 each with 6 soft rays, stand close behind the break 

 in the ventral contour of the body, and they are 

 connected with the anal fin by a thin transparent 

 ridge. The anal, commencing about under the 

 rear end of the base of the soft rayed part of the 

 dorsal, is notched midway of its length ; its forward 

 part is supported by 7 rays close together, the rear 

 part by 5 shorter rays spaced more widely. The 

 caudal fin is forked. A noticeable feature is that 

 the ventral edge of the deep forward part of the 

 body, from the pectoral spur to the pubic spines, 

 is sharp, with a series of 12 hard, plate-like scales 

 or scutes, that extend for some distance up the 

 sides, each slightly overlapping the next rearward, 

 and the profile is saw-edged between the ventral 

 and anal fins. 



The hatchetfishes are provided with a complex 

 system of conspicuous light-producing spots. The 

 species aculeatus has one row of 12 very low down 

 along each side of the deep forward part of the body ; 

 also, a second row higher up consisting of 6 in front 

 of each pectoral fin, 2 along the base of the pectoral, 

 6 between pectoral and ventral fins, 4 between the 

 ventral and the anal fins, 6 along the anal, and 4 

 very small ones between anal and tail fins. There 

 is also one light-organ a little below and behind 



1 Most of the published Illustrations of Argyropelecus fall to show this. 



