6 GEORGE V SESSIONAL PAPER No. 38a A. 1916 



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11. 



NOTES ON THE EGG AND LARVAL STAGES OF THE HALIBUT. 



^ By Professor Edward E. Prince, LL.D., D.Sc, E.R.S.C, etc., 



Dominion Commissioner of Fisheries, and International Commissioner (under the 



Fishery Treaty, 1908). 



(With one plate.) 



It is a well-known fact that the eggs of most of the important marine food-fishes, 

 with such exceptions as the herring and the smelt, produce small buoyant eggs which 

 float in the open sea, usually in the surface waters. They are so small that they 

 escape notice, though in certain areas at the proper season of the year the sea within 

 a fathom or two of the surface abounds with these floating eggs. As a rule, each egg 

 floats single and separate, though occasionally, as in the angler or goose fish (Lophius) 

 the eggs may be immersed in a long band or a mass of clear jelly-like substance and such 

 egg bands are readily discernible in the open sea. In size, these floating eggs range from 

 one-thirtieth to one-seventieth of an inch in diameter, and such vast numbers of 

 them occur in the upper waters that a fine-meshed tow-net, of silk or cheesecloth, will 

 secure great quantities; but, owing to their small size and colourless translucency, 

 they may escape the notice of an ordinary observer. It is estimated that the eggs of 

 over 250 species of marine fishes (Teleosteans) have been described, out of probably 

 80,000 to 90,000 species of fishes inhabiting the seas of the world. 



RIPE HALIBUT EGGS DESCRIBED. 



J So far as is known, the largest of all these eggs is that of the halibut, yet it has 

 niore rarely been seen than those of any other species described by fish-embryologists. 

 Ripe unfertilized eggs of the halibut have been obtaind live or six times during the 

 last twenty-five years by marine biologists, the first being discovered by the leading 

 European authority. Prof. W. Carmichael Mcintosh, of St. Andrews, Scotland, who, 

 in April, 1892, secured some ova from a ripe female halibut caught about 1.50 nnles 

 ENE. from Peterhead, Aberdeenshire. The eggs varied in diameter from one-sixth 

 to one-eighth of an inch (3.07-3-81 mm.), or more than three times the size of the 

 eggs of cod, haddock, or flounders. At the end of the same month Mr. Holt, who had 

 been Professor Mcintosh's assistant at St. Andrews, secured some halibut eggs at 

 Grimsby, but though they were ripe and translucent they sank to the bottom when 

 placed in a vessel of sea-water. Dr. H. C. Williamson later obtained ripe halibut 

 eggs, and he noted the presence of a membrane-like covering, enveloping the yolk, 

 quite separate from the external capsule of the vitelline membrane. In all cases the 

 eggs were described as spherical, translucent, and clear, exhibiting no shining oily 

 gloubles or other floating bodies in the ball of the yolk fluid. The outside capsule, as 

 Professor Mcintosh stated, was found to be extremely thin and marked with delicate 

 " cross-hatching " or short intersecting lines. Indeed they easily collapse, when placed 

 on a glass slip, after removal from water, being compressed by capillary attraction, 

 and usually bursting. Most of these pelagic eggs, though so minute, transparent, and 

 delicate, have some resistance, and can be gently rolled between the finger and thumb 

 when, as Dr. Francis Ward said of plaice eggs, " they feel hard and shot-like," but 

 the eggs of the halibut are unusually frail and collapsible. 

 38a— 2i 



