MIGRATIONS OF COD 
97 
Undoubtedly there is some correlation between temperature and the desire of 
the cod to take food, but we know comparatively little on this subject with respect 
to the various “races” of Gadus callarias. Certainly we coidd expect Labrador cod, 
living in a temperature of, say, —1° to +5° C. to behave differently than Nantucket 
cod living in a temperature of 2° to 15° C. Yet even the latter fish do not cease 
feeding in the winter when the temperature drops below 3° C. 
Along the New England coast an examination of cod stomachs at different 
seasons has shown that more food is eaten in summer than in winter. This, of course, 
may be due as much to a falling off in the food supply as to a loss of appetite due to 
a low temperature, for in February, 1928, off Delaware Bay, we found that instead 
of the cod being on their regular feeding grounds in 4° to 5° C. water they were 
around and inside the bay feeding on sand eels ( Ammodytes ) in about 2° C. water. 
Cutler (1918, p. 488) kept flounders and plaice in water of various temperatures, 
made observations on the scales, and concluded that the amount of food did not 
affect the production of summer and winter bands, but that the formation of wide 
sclerites (generally produced during rapid growth) was due to high water temperatures 
while low temperatures resulted in narrow ones. 
Winge (1915, p. 18), in his work on cod scales, sums up the effects of temperature 
and food on the growth of the cod, as follows: “Everything seems to indicate that 
the rate of growth of the cod is highly dependent upon conditions of temperature in 
the water, although perhaps in the main indirectly through the effect of temperature 
upon the quantity of nourishment.” 
Some light is thrown on the effects of temperature in retarding or increasing 
the rate of growth of cod fry by observations made in Norwegian waters. Dannevig 
(1925, p. 7) cites a rearing experiment carried out by Capt. G. M. Dannevig in 1886. 
At that time newly hatched cod larvae placed in a pond, grew from a length of 
3 millimeters on April 26 to an average length of 10 millimeters by May 31. A 
second experiment of the same sort, but made later in the spring, was carried out 
near Arendal on May 25, 1909, where Dannevig (1919, p. 45; 1925, p. 8) released 
about 100,000 1 to 2 day old cod larvas (4 millimeters long) in the station’s rearing 
pond in water having a temperature of 9.5° C. The larvae grew as follows: June 12 
they averaged about 20.5 millimeters (2 fish); June 16, 27.5 millimeters (2 fish); 
and on June 18, 24.5 millimeters (8 fish). The temperature in the pond on June 16 
was 20° to 21.4° C. and must have been considerably warmer than that which obtained 
during the experiment in 1886. This difference is reflected in the rate of growth, 
for whereas the cod in 1886 averaged only 10 millimeters in length at 35 days old 
(April 26 to May 31), those reared in warm water in 1909 had reached a length of 
about 25 millimeters in 25 to 26 days (May 23-24 to June 18). Although other 
factors, such as the food supply, may have had some influence in bringing about 
this difference in rate of growth, it seems obvious that temperature played the most 
important part. 
H. Thompson (1926, p. 6) is inclined to believe that the amount of food more 
than temperature decides the rate of growth, although haddock and gadoids which 
he had under observation in aquaria had a lessened desire for food from January to 
March. He concluded that, in general, captive haddock living in water of about the 
same temperature as at sea but supplied with a regular diet grow about twice as fast 
as they would under natural conditions. 
