428 



BULLETIN OF THE BUREAU OF FISHERIES 



It is intei-esting to note that on the whole cod spawn in rather colder water 

 in the Gulf of Maine (stiU more so in the Gulf of St. Lawrence and on the New- 

 foundland Banks) than on the other side of the North Atlantic or about Iceland, 

 where the chief production of eggs takes place at temperatures of 40° to 45°. 



The salinities in which cod spawn in the coastwise waters of the Gulf of Maine 

 depend on the precise locality, depth, and season. Probably none spawn in water 

 fresher than 32 per miUe " nor saltcr than 32.8 per miUe, either on the Ipswich Bay 

 grounds or on the Massachusetts Bay grounds, and as far as our records go they 

 point to a salinity of about 32.6 per mille as typical for the spawning of the cod 

 on Georges Bank. This is water much less saUne than ripe cod seek in European 

 seas,'^ and necessarily so, the Gulf of Maine being decidedly fresher at all times 

 (p. 443) than the Norwegian Sea or than the waters around Iceland. 



On the Massachusetts Bay spawning ground the density of the water is high 

 enough to insure the flotation of the eggs throughout the breeding season, but in 

 Ipswich Bay the spring freshets often so freshen the surface that late-spawned cod 



FiQ. 213.— Diagram of the pigmentation of the youngest larvae of cod (a) and American pollock (b). After'Schmidt 



and haddock eggs may fail to rise to the uppermost water layers, a phenomenon 

 which hinders the operations of the hatchery but which does not militate against 

 the successful incubation of the eggs in nature, since they would merely float 

 suspended at some deeper level. This subject is discussed at greater length in 

 connection with the haddock (p. 443). 



The cod is one of the most prolific of fishes, so much so that a female 39 or 

 40 inches long may be expected to produce about 3,000,000 eggs and one of 41 

 inches at least 4,000,000. Earll estimated the number in a 52H-inch fish weighing 

 51 pounds at 8,989,094, with 9,100,000 in a 75-pounder. 



The eggs are buoyant, transparent, without oil globule, and 1.16 to 1.82 mm. 

 in diameter. Gulf of Maine eggs, artificially fertihzed and measured by Welsh, 

 averaged about 1.46 mm. in diameter. 



" The surface may be much fresher in spring, but not the bottom water in which the fish are lying. 

 " 34.5 to 35 per mille, according to Damas. 



