The Growth of Fish

Abstract

ABSTRACT For the egg of any given species of animal there exists a range of temperature within which the embryo is capable of developing into a normal healthy organism. If the temperature of incubation be raised, the velocity of development of a cold-blooded embryo is increased ; if the temperature be lowered the velocity is decreased. In both cases the result is qualitatively similar; the mutual proportions of the various tissues and organs are, as far as is known, much the same in the final products. It is improbable that the velocity of every process which occurs during development is equally affected by changes in temperature; some processes will tend to respond to a greater extent than others. If, therefore, development were simply the summation of each separate process we would expect to find that the relative size of each organ would vary with the temperature at which the egg had been incubated. Consider, for example, two cells each capable of reproducing itself in 12 hours at 10° C. but differing from each other in their temperature coefficients of growth. If a rise of 10° C. increased the rate of development of one cell by 100 per cent., and that of the other by 200 per cent., then at the end of 12 hours’ development at 20° C. there would be five cells of one type for every seven of the other, whereas at 10° C. the numbers would be equal. The very fact that marked variations in the proportionate size of organs and tissues do not apparently characterise variations in the temperature of incubation indicates that, to some extent, the velocity of development of any one type of tissue or the velocity of any one embryological process is dependent on the velocity of other parallel processes, or that they are all controlled by the velocity of one fundamental reaction. By varying the temperature of incubation of the eggs of the trout, a convenient means exists of determining how far this picture of the embryological development of a fish is true, or how far some processes can be regarded as independent reactions.