Metabolic rate is widely regarded a

Metabolic rate is widely regarded as a universal currency in animal biology and ecol-
ogy, providing an objective measure that can be used in attributing a cost to different
activities and specifically helping to assess what animals do against some optimal behaviour. In their seminal paper, Brown et al.(2004) pro-posed that, ‘Metabolism provides a basis for using first principles of physics, chemistry,and biology to link the biology of individual organisms to the ecology of populations communities, and ecosystems’. From an ecological perspective, attributing a biologi-
cally meaningful cost to specific activities under different environmental circumstances
helps to inform a wider understanding of the selective advantage of making trade-offs
between different activities.
For fishes, understanding the balance of costs and benefits is complex. Most fishes
are ectothermic, with body temperatures and therefore metabolic rates affected by their
local thermal environment. Although movement in an aquatic environment is less costly
when compared with terrestrial or aerial animals (Schmidt-Nielsen, 1972), understand-
ing the balance of costs and benefits is further complicated by the patchy and relatively
(assumedly) unpredictable distribution of resources,e.g. food and oxygen, in space and
time, making it effectively impossible to predict, from basic principles, how a fish is
likely to respond to a given external environmental situation or internal physiological
state or need.