394 BULLETIN OF THE BUREAU OF FISHERIES 



In the case of any fish producing buoyant eggs the tendency of the latter to 

 rise insures (unless it be counteracted by active vertical circulation of the water) 

 that development shall take place in the temperature of the surface layer, not of 

 the deeper lying water in which they are spawned. In most parts of the Gulf of 

 Maine, too, where the surface is much warmer than the underlying water strata 

 in summer, it follows that buoyant eggs produced as much as a few fathoms down 

 incubate, and the larvae at hatching find themselves in temperatures considerably 

 higher than those in which spawning takes place. The silver hake is no exception 

 to this rule. While we have towed its eggs in June when the surface was still only 

 about 42°, most of the egg records, with all the rich catches, were made in temper- 

 atures ranging from 51° to 63°; and at the few localities where we have taken 

 newly hatched larva? (less than 4 mm. long), the upper stratum of 5 fathoms or so, 

 where hatching may be assumed to have taken place, has invariably been warmer 

 than 50° and usually warmer than 55°, with the temperature of the immediate 

 surface 60° or higher in most cases. Such evidence suggests that incubation does 

 not proceed normally in water cooler than about 50°, and that development is most 

 successful in temperatures as high as 55° to 60°. Thus, though the silver hake 

 may spawn in low temperatures, a comparatively warm surface layer is necessary 

 for the later stages in its propagation. This is interesting in its application to 

 the Gulf of Maine for it offers a reasonable explanation of the failure of this fish 

 to breed successfully along the New Brunswick shore of the Bay of Fundy, where 

 active vertical circulation maintains surface temperatures as low as 50° to 55° 

 throughout the summer. On the other hand, however, the failure of the eggs 

 to develop in the hatchery at Woods Hole points to 65° to 70° as the upper limit 

 to successful incubation. 



Spawning takes place in comparatively low salinities in the Gulf of Maine, 

 with a vertical range at the "egg" stations of from about 31.5 to about 32.5 per 

 mille, while 33 per mille may be set provisionally as the maximum salinity in which 

 any silver hake eggs develop in the Gulf, water far less saline than that in which 

 the European silver hake spawns and in which its eggs develop. 



Our frequent captures of silver hake larvre at many localities (fig. 195) prove 

 that it not only spawns freely in the Gulf of Maine but that the eggs develop, and 

 that the southwest part of the Gulf at any rate (p. 395) is a favorable nursery for 

 them. Furthermore silver hake have been the subject of our richest haul of young 

 fish, a 15-minute haul at 20 fathoms with a net one meter in diameter off Cape Cod 

 on July 22, 1916 (sta. 10344) having yielded approximately 25,000 larvae of 3 to 

 7 mm. 



We know of no estimate of the number of eggs a single female may produce. 

 The eggs are buoyant, transparent, about 0.88 to 0.95 mm. in diameter, with a 

 single yellowish or brownish oil globule of 0.19 to 0.25 mm. Incubation is rapid; 

 Kuntz and Radcliffe assumed 48 hours at Woods Hole, but its duration has not been 

 determined for the cooler water in which the eggs are produced naturally in the 

 Gulf of Maine. The larva? are about 2.8 mm. long at hatching, slender, with com- 

 paratively small yolk sac, and recognizable by the facts that the vent is located close 

 behind the latter on one side near the base of the larval fin fold as in the cod family, 

 not at its margin as in most larval fishes, and that the trunk behind the vent is 



