FISHES OF THE GULF OF MAINE 



515 



summer a difference of only a few fathoms in the depth at which the eggs or young 

 larviB are suspended means a difference of several degrees of temperature. 



The eggs are buoyant, spherical, transparent, with narrow perivitelline space 

 (in plaice eggs, which overlap them in dimensions, the perivitelline space is broad), 

 without oil globule, and 1.07 to 1.25 mm. in diameter. As noted elsewhere (pp. 429 

 and 443) , there is danger of confusing newly spawned witch eggs with those of cod or 

 haddock, for they overlap in size and in season; but identity as witch or as gadoid 

 is easily recognizable after a few days' incubation, for black pigment is to be seen in 

 the latter soon after the embryo is visible as such but does not appear in the witch 

 until after hatching, such embryonic pigment as is visible in the egg being of a faint 

 yellowish color. 



Incubation occupies 7 to 8 days at temperatures varying from 46° to 49° F., 

 and the newly hatched larva is about 4.9 mm. long with larger yolk sac than our 

 other flatfishes. Within a few days after hatching, when the larva is 5 to 6 mm. 

 long, the yellow and black pigment becomes aggregated into 5 transverse bands 

 on body, yolk (now much reduced in size), and fin fold — that is, 1 at the region 

 of the pectoral fin, 1 at the vent, and 3 on the long slender postanal part of 

 the trunk. The yolk is entirely absorbed in about 10 days after hatching; at a 

 length of 15 mm. the caudal rays have begun to appear, at 21 mm. those of the 

 vertical fins are well advanced, and at about 30 mm. they are complete in their final 

 number. Up to this stage the eyes are still symmetrical or nearly so, but in larva? 

 of about 40 mm. the left eye has moved to the dorsal surface of the head, while at a 

 length of 40 to 50 mm. the migration of the eye is complete and the young fish takes 

 to the bottom. 



The witch is perhaps the most easily recognizable of Gulf of Maine flatfishes 

 throughout its larval stage. Prior to the appearance of the caudal rays the trans- 

 verse pigment bars are diagnostic, and thereafter it is characterized by the curiously 

 concave ventral profile of the throat region and by its comparatively long slender 

 trunk, while the great number of dorsal and anal rays, coupled with the small mouth, 

 make identification easy after the fins are formed. The witch grows to a larger 

 size before metamorphosis than any other of the right-handed, small-mouthed 

 species found in the Gulf of Maine. 



Measurements of the young, American as well as European, show that the 

 pelagic stage lasts from four to six months. The result of their remaining near the 

 surface so long, combined with the protracted spawning season, is that larva? of 

 various sizes may be towed throughout the summer in the Gulf of Maine, as appears 

 from the following table of our catches on the Grampus: 



