96 
BULLETIN OF THE BUREAU OF FISHERIES 
direct evidence, these-grounds are adjacent to Nantucket Shoals and support a large 
stock of fish. Another indication that a large part of the Nantucket adult cod are 
derived from near-by regions and not from the northward is to be had from scale 
studies which have shown that the cod to the north of Cape Cod differ materially 
from those to the southward in the early growth of their scales (p. 110). 
AGE AND RATE OF GROWTH OF COD, PARTICULARLY THOSE ON NANTUCKET SHOALS 
On the present investigation we did not specialize in a study of the factors which 
cause fluctuations in growth other than the collections of water temperatures and 
observations on the cod’s food. We were concerned, however, in determining the 
growth of the cod in various parts of its habitat along the New England coast and in 
doing this utilized three methods, namely, length frequencies, scales, and growth 
registered by recaptured tagged fish. 
Many observations have been made, especially in European waters, on the 
age and rate of growth of cod. The majority of the records obtained cover only 
the first year of growth, because most of the collections have been of young fish 
that were obviously in their first year of life. Even up to the completion of the 
second year records are not lacking, but above this age data become fewer and fewer 
as the fish grow older. 
There is no particular rate of growth nor any average size at a given age that 
will cover the cod for all parts of its range. Environmental conditions affect growth 
in some cases to a marked degree, for in general the cod in Europe appear to grow 
more slowly than off the coast of America, and growth evidently is more rapid in the 
southern part of the fish’s range than in the northern. 
There has been much discussion as to whether food or temperature is the more 
important in regulating the growth of fish and various experiments in this direction 
have been undertaken. 
Fulton (1904, pp. 170-171) believed that temperature was of first importance 
because it acted directly on the metabolism of the fish and affected the rapidity of 
digestion. He pointed out in his experiments with cod, haddock, and other species 
that fish gave up feeding altogether when the water became very cold (less than 3.8° 
C.), because under such conditions the ferments upon which digestion depends 
acted slowly or not at all. Appetite waits on digestion, and the latter may be cor- 
related with the metabolism in the tissues. Cod and haddock living in cold-water 
aquaria in the winter were sluggish and moved about very little, whereas fish kept 
in artificially heated aquaria were very active and had a good appetite. However, 
3.8° C. does not mark a critical temperature below which all cod cease feeding, for 
in some of the regions where cod live the year around, as off Labrador, Greenland, 
Iceland, and on the Grand Bank, the temperature is below 3.8° C. most of the time. 
Jensen (1926, p. 91), fishing for cod ( Gadus callarias) off the west coast of Greenland 
with hooks baited with frozen herring, caught virtually no fish during June, when the 
bottom temperature on Fyllas Bank ranged from 0.20° to 1.06° C., but made good 
catches early in July at temperatures of 0.87° to 1.68° C. and again the middle of 
the month at 2.09° to 2.74° C. and Hjort and Kuud (1929, p. 17) record that the 
Michael Sars found excellent hand-line fishing for cod on August 5, 1924, in latitude 
63° 55' N., longitude 53° W., in 67 meters, where the temperature was about 1.6° 
C. The cod had been feeding on shrimps, amphipods, crabs, and sand eels. Cod in 
this region, therefore, feed when the temperature is appreciably below 3° C. 
