EGG AND LARVAL STAGES OF HALIBUT 21 



SESSIONAL PAPER No. 38a 



proved the diagnosis incorrect. Thus, Dr. H. M. Kyle, an able original worker in 

 this field of research, described two larval flat fishes, 12 and 14 mm. in length, re- 

 sipectively, secured in August in the Moray Firth, Scotland, and regarded as probably 

 larval halibut, though it was also thought that they might prove to be young pole-dab 

 (P. cynoglossus). The description and published drawings (Plate iii, Journ. Mar. 

 Biol. Assoc, Plymouth, vol. vi. No. 4, December, 1903) attrrcted the attention of 

 specialists and resulted in favour of the latter determination, and Dr. Kyle, in a 

 final foot-note (ihid., p. 621), said: " At first I was disposed to regard them definitely 

 as young halibuts, but from a drawing sent to him, Mr. E. W. L. Holt is inclined to 

 regard them as pole-dab." Similarly, the staff of the United States biological steamer 

 Albatross, regarded four specimens of flat fish as halibut which had been eaiuured 

 dO or 70 miles off the New Jersey coast (39 :45 N. lat., 73 :49 W. long.) about the end 

 of May, 1887, at the surface of the sea; but they were clearly not halibut, from 

 certain diagnostic features which they presented. Thus they showed coloured trans- 

 verse bands, and the dorsal fin possessed about 80 rays, though the fish were only 17 

 mm. long (seven-tenths inch), whereas the halibut does not exhibit a transverse 

 arrangement of pigment spots until it is much larger, 27 mm., or over an inch long, 

 and rarely fewer than 100 fin rays in the dorsal fin. The two species of halibut now 

 recognized, viz., Hippoglossus hippoglossus Linn, (or H. vulgaris Flemming) has 90 to 

 103 rays in the dorsal fin, and Platysomatichthys hippoglossoides Walb., has 96 to 108 

 rays in the same fin. Conjointly with other features, if any specimen has 100 

 rays or more it is unquestionably a halibiat. But the number of joints or vertebrae 

 in the backbone is even more distinctive, for H. hippoglossus has usually fifty, and 

 P. hippoglossoides has sixty-two vertebral' elements, and the anal fin, it may be added, 

 has seventy-one to eighty-three rays in the former and sixty-seven to seventy-nine in 

 the latter species. The well-known specimen of supposed halibut procured by Dr. 0. 

 G. S. Peterson, of the Danish Zoological Station, in the waters of Christiansund is 

 now known, like that of Dr. Kyle, to be almost certainly a specimen of the witch oi 

 pole dab. It was 32 mm. (1§ inch) in length and had 104 rays in the dorsal fin, eighty- 

 eight in the anal, and twenty-two in the caudal, and the gill cover exhibited a row of 

 spines. This last feature is one which demonstrates the specimen not to be a halibut. 

 Dr. Peterson's larger specimen obtained in Greenland in 1893 in May and measuring 

 51 mm. (over 2 inches) in length has seventy rays in the anal fin, but the halibut has 

 more rays — not less indeed than seventy-three rays in P. hippoglossoides^, and eight.v- 

 two to eighty-three in H. hippoglossus. 



'lOUNG LARVAL HALIBUT DESCRIBED. 



It is due to the accomplished Dr. Jos. Schmidt, the Danish biologist, that the 

 youngest stage of the halibut obtained up to the present has, been determined. The 

 specimen was 13-5 mm. long, over half an inch (or -531 in.) and it had still the worm- 

 like form and symmetrical upright position of llo early larva (PI. I. fig. 1), All 

 the flat fishes (Heterosomata) undergo a transformation before they lie permanently 

 on one side with both eyes on the same surface. " Plat-fish larvae," as Dr. Ward says,, 

 "begin by swimming near the surface in an upright position like the larvae of other 

 fishes. Next, they flatten from side to side, and gradually approach the bottom, to 

 end up by lying on their right or left sides as the case may be. . . . Plaice, soles, 

 bounders, dabs, lemon soles, and halibut, after they have flattened, all lie on their left 

 side, while turbot and brill lie on their right side." One eye moves to the other side 

 as the transformation proceeds, so that both eyes are found on one side of the fish in 

 the permanent flattened condition. Thus the halibut, when it hatches out of the egg, 



1 Dr. Gilpin, of Halifax, gave the number as seventy-four or seventy-five rays (loc. cit., v 

 21) for Nova Scotia specimens. 



