254 
BULLETIN OF THE BUKEAU OF FISHEEIES 
it would appear that the growth rate of the cisco in these lakes depends primarily 
on some factor other than that of the productive capacity of the lake as that capacity 
is estimated from the concentration of bound C0 2 in its waters. If it is assumed 
that the various stocks do not differ greatly in their hereditary capacities for growth 
and that environmental conditions are in general comparable, then it may be expected 
that the amount of growth in the various populations will depend in large measure 
upon the availability of food. The determining factor is then the amount of food 
available to each individual fish. If the poorest growth occurs in the lake that 
produces the greatest amount of food, it may be assumed that here in all probability 
the number of feeding individuals is so great and the competition for food so strong 
that these individuals cannot secure a sufficient amount of food to maintain their 
normal rate of growth. On the other hand, if a relatively rapid growth occurs in a 
lake with a scanty basic supply of food it may be assumed that the feeding popula- 
tion in that lake is so small that in spite of the scarcity of food the individuals are still 
able to secure sufficient nourishment to maintain rapid growth. 
This conception of a dependence of growth upon density of population is based 
primarily upon the assumption that there exists a competition for food. If food is 
present in a quantity greater than the maximum which the population can utilize 
for purposes of maintenance and growth, then an increase in the density of the popu- 
lation should not affect its growth rate until that point is passed where the food avail- 
able becomes less than the maximum quantity which the population can use. From 
this point on a continued increase in the density of population involves a decrease 
in the ration of the individual fish and reduces the amount of individual growth. If 
the density of the population becomes sufficiently great, there is finally reached the 
point at which the food supply suffices only for purposes of maintenance and there 
is no excess for growth. 
The evidence that investigators have presented to show a relationship between 
density of population and rate of growth in fishes has been of two sorts: (1) Change 
in rate of growth accompanying transfer from a thickly populated to a sparsely popu- 
lated region, and (2) change in rate of growth accompanying changes in the density 
of the population within the same region. 
European investigators have conducted numerous experiments that show the 
effect on growth rate of transplanting young plaice from the overcrowded coastal 
nursery grounds to less densely populated areas with more abundant food. The 
classic of all such experiments is the Danish work of transplanting young plaice from 
the overcrowded nursery grounds at the entrance of the Limfjord to the thinly popu- 
lated areas of the inner broads. Although three-fourths of the fish are retaken within 
the year following the time of their liberation, their increase in size is so great that a 
continuation of these transplantation operations, which were begun in 1892 , has 
proved profitable up to the present time. 17 
Borley ( 1912 ) gave the results of experimental transplantation of plaice from the 
English coastal waters to the Dogger Bank. He believed that there was “at least a 
doubling of the growth” (in length). In the same paper Borley reviewed the results 
of similar experiments by Dutch and Danish investigators. Lee and Atkinson ( 1912 ) 
also reviewed the results of earlier transplantation experiments. A good general review 
of European plaice transplantation experiments may be found in Blegvad’s paper 
published in 1933 . 
17 There was no transplantation in 1917. Johansen (1928) summarized the results of the transplantation operations in the 
Limfjord up to that time. 
