(1892), state that cod are killed in water 

 of -1.1°. Contrast this with spawning 

 reported at this temperature (Bigelow and 

 Schroeder 1953). A. Dannevig (1930) says 

 that at the Fltfdevig Hatchery cod have been 

 held on occasion in water near -1° with 

 only partial mortality. 



McKenzie (1956) quotes a personal 

 communication from A. H. Leim to the effect 

 that a 52 centimeter cod in a tank evi- 

 denced no discomfort until the temperature 

 reached -1.2°, although respiration ceased 

 only slightly below this, at -1.5", and 

 heartbeat at -1.9°. Thompson (1943) reports 

 that cod died when transferred from 0°, 

 where they had apparently been doing well, 

 to -0.6°. He considers that the lethal 

 point lies close to -2° . 



At the other extreme, McKenzie (1935) 

 says that most of the large cod in tanks 

 died when the temperature reached 15.0* , 

 and that 20.0* was fatal to all large fish, 

 although smaller ones survived. 



Apparently the lethal temperatures 

 for cod are somewhat variable, probably 

 depending to a certain degree on what the 

 fish have been conditioned to previously 

 and how suddenly the temperature changes. 

 But generally we may conclude that under 

 appropriate circumstances some cod can sur- 

 vive from temperatures near the freezing 

 point of sea water to 20.0*. Of particular 

 interest are the relatively small variations 

 in temperature near the freezing point which 

 may cause large changes in behavior and 

 death — v. Leim's cod which appeared comfort- 

 able and died of cold all within a range of 

 0.7*. 



Sundnes (1957) reports that cod are 

 asphyxiated when the oxygen content of the 

 water is 0.80 ml. per 1. or less. 



RECAPITULATION 



Cod are indeed influenced by the 

 hydrographic conditions in the waters they 

 frequent . 



The maximum range of temperature for 

 spawning is from below 0° to about 12°, 

 with cod on European coasts spawning only 

 over the lower half of this range. There 

 is some evidence that cod leave the bottom 

 and school pelagically to reproduce, and a 



suggestion that the thermocline is the 

 preferred spawning habitat in some areas. 

 Salinity seems to have very little influ- 

 ence on spawning. 



Cod eggs can develop from below zero 

 to about 14°, and the optimum temperature 

 for the eggs and the larvae which hatch 

 from them is probably from 5° to 7*. Eggs 

 and larvae are subject to the effect of 

 salinity change, with a critical point for 

 survival perhaps in the neighborhood of 

 15°/oo, although there seems to be no natu- 

 ral upper limit. In many areas eggs and 

 larvae are found in intermediate layers of 

 water when surface salinities are not suf- 

 ficient to cause them to float, that is, 

 when they are below about 25°/oo. In the 

 critical young stages, transport by currents 

 and perhaps severe storms can be dangerous 

 to the helpless eggs and nearly helpless 

 larvae. 



Cod growth varies with temperature; 

 they grow more and apparently faster where 

 the water is warmer. This is related to 

 feeding, which takes place in roughly the 

 full range which cod can endure, with 

 smaller cod generally tending to feed more 

 than the large at higher temperatures. It 

 seems likely that reduced feeding at very 

 low temperatures is related to metabolic 

 function so that cod in very cold water 

 actually cannot feed. 



It does not seem possible to find a 

 hard and fast definition of "cod water". 

 This is perhaps because the distribution 

 of feeding cod is more dependent on the 

 distribution of the prey than it is on tem- 

 perature per se. However, whatever the 

 reason, larger fish are found in colder 

 temperatures, and the optimum on the Grand 

 Bank seems to be from 0* to about 5° , and 

 on the Nova Scotian banks the optima are 

 roughly the same. On the Labrador banks 

 and the Gulf of St. Lawrence, the optima 

 are slightly higher, as they are in the 

 Spritzbergen-Bear Island area. Cod live 

 in almost every salinity from nearly fresh 

 water to full oceanic salinity about 

 35°/oo. 



The internal temperature of the cod 

 is similar to that of the ambient water, 

 but in spite of this cod live in water of 

 a wide range of temperatures, from nearly 

 the freezing point to water considered 

 comfortable for human bathing (20°). At 



10 



