discontinuity layer. Poulsen observes that 

 cold temperatures in the months preceding 

 spawning may have considerable effect in 

 delaying the maturation of the gonads, and 

 A. Dannevig's (1947) conclusions concerning 

 the 1938 year class in the Transition Area 

 agree. 



Various theories about preferred and 

 optimum temperatures have been advanced 

 without supporting evidence. Damas (1909) 

 states that European cod spawn at tempera- 

 tures from 2° to 6° and that the optimum is 

 probably above 4°. An American opinion 

 (Anonymous 1932b) is that cod on our coasts 

 prefer temperatures between 3* and 5°, and 

 that they gather ready to spawn it about 

 2.5°. 



A few instances of captive cod spawn- 

 ing in tanks or live cars have been recorded, 

 and these cite temperatures from as low as 

 -1.1* (Bigelow and Schroeder 1953), to a 

 range of 0° to 5* (A. Dannevig 1919), to 

 voluntary spawning at 5.5* (Anonymous 1911). 



On the American side of the Atlantic, 

 in the ocean, spawning temperatures are 

 reported variously as from 0.6° to 8.9° 

 (Bigelow and Schroeder 1953), 0.56° to 10.1° 

 (Fish 1929), 8« to 12° (Tremblay 1942), and 

 7° to 12° (McKenzie 1934b). It should be 

 understood that some of these authors were 

 describing individual groups of fish and do 

 not claim that these are spawning ranges 

 for all cod in the Northwest Atlantic. 



Schmidt (1926) reports little or no 

 spawning at Iceland below 6*. Spawning at 

 6° is recorded for one year on the Norwegian 

 coast and in the fjords by Hjort and Peter- 

 sen (1905), although they mention that this 

 was an exceptionally warm year. Sund (1935> 

 describes cod seen in pelagic spawning con- 

 centrations on echosounding traces at 

 Lofoten from 3° to 6.5°. 



In the Barents Sea the maximum accumu- 

 lation of cod eggs at the surface is found 

 in areas where the bottom temperatures are 

 0* to 2" , although Rass (1936) considers the 

 possibility of pelagic spawning in upper 

 layers where a more moderate 3° to 4* is 

 found. He speculates that the difference 

 between the spawning temperatures off the 

 Murman coast and those along the Norwegian 

 coast (see above) may be a possible indica- 

 tion of a racial difference in the stocks 

 of cod. 



Poulsen (1931) describes spawning in 

 Danish inner waters where the preferred 

 temperature seems to be 3° to 7°, although 

 extremes of 2" and 8° have been observed. 



To sum up, actual observations of cod 

 spawning in captivity prove that tempera- 

 tures from -1.1° to 5.5° are physiologically 

 possible. Indirect evidence from distribu- 

 tion of eggs on the surface, concentrations 

 of fish in the spawning season, etc., indi- 

 cate a range of from 0.6° to 12° in the 

 Northwest Atlantic, and from about 0° to 

 6.5* in the Northeast Atlantic, with the 

 extremes of all observations be.>g from 

 -1.1° to 12". There is some evidence that 

 cod will leave the bottom and school pelag- 

 ically to spawn at a suitable temperature. 

 Not to be neglected is the idea of some 

 Scandinavian workers that variation in tem- 

 perature in the water column rather than 

 temperature per se may be the determining 

 factor. 



Salinity, oxygen and pH 



Damas (1909) states that cod on Euro- 

 pean coasts spawn at about 34°/oo - 35°/oo 

 salinity, while Bigelow and Schroeder (1953) 

 think it is probable that no American cod 

 spawns at less than about 32° /oo nor more 

 than 32.8°/oo, giving a figure of about 

 32° /oo for Georges Bank. Damas, however, 

 cites 35.16°/oo for the Grand Bank. One 

 anonymous source (1932b) says that cod 

 "prefer" 33°/oo to 34°/oo on American 

 coasts. In general we may agree with Bige- 

 low and Schroeder that American cod spawn 

 at lower salinities than do European, with 

 the exception of Baltic cod, which spawn at 

 about half the usual oceanic salinity. 

 Whether the matter of salinity at spawning 

 time is strictly coincidence or whether 

 salinities may induce or delay spawning 

 seems to be an unanswered question. 



Sund (1935) cites an instance in which 

 cod were found spawning pelagically in layers 

 of water which had appreciably lower concen- 

 trations of oxygen and lower pH than the 

 adjoining layers above and below, but gives 

 no values . 



EGGS AND LARVAE 

 Temperature 



A relation between temperature of 



