262 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Figure 131. — Larva (European), 9 mm. After 

 Ehrenbaum. 



Figure 129. — Egg (European). After Cunningham. 



Figure 132. — Larva, 14.5 mm., off Massachusetts Bay. 



Figure 130. — Larva, just hatched, 4 mm. (European) 

 After Mcintosh. 



Figure 133. — Larva, 22.5 mm., off Cape Cod. 

 Canadian plaice, or Dab {Hippoglossoides plaltessoides) . 



This space is formed by the entrance of water 

 between the egg proper and its covering mem- 

 brane, after the eggs are shed, and it about 

 doubles the total diameter of the egg. The eggs 

 we have taken in the Gulf of Maine have averaged 

 about 2.5 mm. in diameter, but they have been 

 reported as small as 1.38 and as large as 3.2 nun. 

 in other seas, depending on the breadth of the 

 perivitelline space. 



Incubation occupies 11 to 14 days at a tempera- 

 ture of 39° F., and it seems that the eggs gain 

 weight as development proceeds, for Huntsman 

 found, in the Gulf of St. Lawrence, that the 

 newly spawned eggs floated at the surface, but 

 that eggs nearly ready to hatch drifted suspended 

 at a depth of some 10 fathoms. We have no 

 first-hand information to offer on this point. 



During the development of the egg, minute 

 black and yellow pigment cells are scattered 

 over the embryo, not aggregated into any diag- 

 nostic clusters. But the pigment gathers in five 

 definite groups very soon after hatching (which 

 takes place when the larvae are 4 to 6 mm. long) ; 

 one on the gastric region, one about the vent, and 

 three behind the vent; a pattern similar to that 

 of the larval witch flounder (p. 287) . 



The yolk is absorbed about 5 days after hatch- 

 ing, when the larva has grown to 6.2 to 7.5 mm. 



in length. The caudal rays appear shortly after 

 this, the dorsal and anal rays at about 11 to 12 

 mm., and the three vertical fins are differentiated 

 at about 15 to 18 mm. By this stage the body 

 has begun to assume the deep but very thin form 

 characteristic of all young flounders, while the 

 jaws have developed sufficiently to show that 

 the little fish belongs to one of the large-mouthed 

 species. The left eye may commence its migra- 

 tion when the larva is about 20 mm. long, while 

 Welsh found it visible above the outline of the 

 snout in Gulf of Maine specimens of 24 mm., 

 and almost at the dorsal edge at 34 mm. But 

 larvae as long as 35 mm. may still be symmetrical 

 in other seas. 



The only other Gulf of Maine species for which 

 the larval dab might be mistaken (except in its 

 very earliest stages) are the witch flounder and the 

 halibut; but the witch is longer at corresponding 

 stages of development, but ■with the distance 

 from snout to vent proportionately much shorter, 

 and the outlines of throat and abdomen are suf- 

 ficiently different to distinguish the dab from the 

 halibut (p. 253). 



The young dab drifts freely up to the time of its 

 metamorphosis, as the young of most sea fishes 

 do; close to the surface at first but sinking deeper 

 as it grows, until it seeks the bottom finally. 



