MIGRATIONS OF COD 
105 
He found that the formation of the closely spaced circuit took place in the late summer 
or autumn and the widely spaced circuit during the winter. Because of this, he states 
that the term “winter zone” should be abandoned and suggests using “zones of 
minimum sclerites, or resting zones.” Dannevig intimates, however (ibid., p. 22), 
that scales taken from cod living under natural conditions might have produced 
different results. Duff (1929, p. 11), who studied the peripheral circuli of cod 50 to 
55 centimeters long caught on the Sable Island Banks (Nova Scotia), found that the 
zone of broad circuli was formed on the scales from March to July, inclusive, and 
most of the narrow circuli from August to December. Such few circuli as formed 
during January and February were narrow. 
Ordinarily the widely spaced circuli on the scales of southern New England cod 
are laid down from April to September or October and the closety spaced circuli dur- 
ing the remainder of the year. Some of them, however, begin adding widely spaced 
circuli as early as February and March and the narrow circuli may start to form as 
eariy as August. Occasionally a fish is found that exhibits rapid scale growth during 
the winter as well as the summer. For example, a sample of 51 adult cod caught off 
Atlantic City, N. J., within the period from March 23 to April 2, 1928, showed the 
following peripheral growth on their scales: 39 fish had only closely spaced circuli; 
11 fish had from 1 to 4 widely spaced circuli, indicating that more rapid growth had 
begun as early as February (if not January) and the beginning of March; while 1 fish 
had 6 very wide circuli, which appeared to represent a full year’s (its fourth) growth. 
In regions where food and temperature fluctuate widely we can expect, and often 
do find, that the scales are more sharply defined as to age than in regions where more 
stable conditions obtain. J. S. Thomson (1904, p. 99) made observations on a whiting 
( Gadus merlangus ) from the time it was a month or so old (10 to 20 millimeters) in 
May, 1902, until it died in July, 1903, and was 8% inches long. The fish had been 
fed regularly during this time and the water temperature in the aquarium was fairly 
constant, although there was a marked difference between summer and winter. 
Upon examination the scales of this fish showed uniform growth, without distinct 
areas of summer and winter growth such as was registered on scales of other young 
whiting taken from the sea. Thomson believed, therefore, that it is variation in food 
supply rather than variation in temperature which influences metabolism and 
indirectly brings about the formation of annual rings on scales. Mention has already 
been made of H. Thompson’s experiments (1926, p. 4), showing increase in growth 
due to an ample food supply; of Fulton’s experiment (1904, p. 162), showing that a 
low water temperature retards feeding and, as he suggests, growth; and of Cutler’s 
experiment (1918, p. 488), from which he concludes that temperature and not food 
caused the summer and winter bands on the scales of flounders. 
Winge (1915, p. 13) throws some light on the role which the environment plays 
in the spacing of the circuli on the cod’s scales. Three of his cod which had been 
tagged August 16, 1911, off the Faroes (about 15, 16, and 17 inches long), were 
recaptured on the same ground, two on May 17 and one on May 25, 1912. Scale 
samples had been taken at the time of tagging and again when the fish were recap- 
tured nine months later. As the fish were recaptured in the same place where they 
had been tagged, it was assumed that they had not migrated away and had lived 
together under the same conditions during that time. Winge plotted curves showing 
the distance between the circuli, utilizing five scales for each fish. Not only did each 
of the five scales from the same fish exhibit the same fluctuations but the scales for 
all three fish showed that they had responded in the same way to environmental 
