Adaptive Aspects of Energy Allocation

Abstract

Fishes, like all organisms, use ingested food resources (C) as building blocks in the synthesis of tissues (production, P) and as fuel in the metabolic processes that power this synthesis and other physicochemical work (R). Some of the resources are lost as waste products (E). All these aspects of metabolism can be represented in energy units (joules; 4.2 J/cal) and, since all biological systems obey the laws of thermodynamics, can be combined as follows:

$$C=P+R+E$$

(1.1)

Total metabolism (R) comprises a number of subcomponents: standard metabolism (R _S), which is recorded when the organism is at rest; routine metabolism (R _R), which is recorded in ‘routinely’ active animals; feeding metabolism (R _F), associated with animals that have just fed (sometimes known as specific dynamic action or effect), and active metabolism (R _A), which is recorded in animals undergoing sustained activity (i.e. swimming in fishes). If the energy demands additional to routine metabolism are additive, then:

$$R = {R_S} + a{R_{R - S}} + b{R_{F - S}} + c{R_{\Lambda - S}}$$

(1.2)

where a, b and c are constants expressing the fraction of time that each type of metabolism is used. P can consist of both somatic (Pg) and/or reproductive (Pr) components. Finally, E can be decomposed to faeces (F), the excretory products such as urea and ammonia (U), and miscellaneous secretions such as mucus (Muc).