Growth and Production

Abstract

Growth is the change in size of the fish. It can be measured as growth in length, in weight or in the total energy content of the fish. Although these measures of growth are usually highly correlated, the correlations between them are not perfect. A period of linear growth need not be accompanied by a growth in weight; a change in the total energy content can take place when both weight and length are unchanged. Both weight and energy content can decline sharply, but shrinkage of the linear dimensions of the fish is slight. If growth is measured in terms of energy, then the concept of a balanced energy budget (Chapter 4) can be used to define growth as the difference between the energy assimilated and the energy expended in respiration, that is:

GROETH=IN—OUT

(Ursin, 1979). This formulation cannot be used to define growth in weight or length, although it is easier to measure growth in these terms.