the trial period 11.7 kJ of energy was released to sustain routine meta-
bolism. From the information given in Figure 5, a fish of condition 2.23
would be expected to derive 43.8% of its energy from fat catabolism and
56.2% of its energy from a protein source. Thus of the 11.7 kJ of energy
required for maintenance, 5.1 kJ would be supplied from a lipid source and
6.6 kJ from a protein source. This, in terms of total tissue mass, represents
130 mg. of lipid and 280 mg of protein or a total of 410 mg of tissue. It can
be estimated that approximately 1,760 mg. of water associated with the
tissue would be simultaneously lost (Figure 6) thus giving a total fresh
mass loss of 2.17 g: a reasonable comparison to the measured loss of 2.02 g.
Similar comparative estimates for various other temperatures are given in
Table 1. The reasonably close values demonstrate that tissue composition as
derived from careful condition factor analysis is a useful and fairly accurate
predictive method to determine composition for detailed respirometry or to
establish the pattern of utilization of catabolic fuels during metabolism
without killing the experimental fish.
1.8 2.0 2.2 2.4 2.6 2.8Relative condition factorFigure 6. The relationship between water content and tissue content for Tilapia rendalli
of varying relative condition factor (after Caulton 1978b).