Physiology of Finfish and Shellfish (2+1)

4.1.5. Metabolic Rate - Temperature Effects

Animals get the energy to sustain life by oxidizing reduced carbon compounds in food, therefore metabolic rate can be measured experimentally by determining an animal's rate of oxygen consumption (mg O₂/kg body weight/hr). Fish can be placed in underwater chambers where their uptake of O₂ can be accurately recorded, moreover the temperature can be varied and the fish can be made to swim. On this type of experimentation, rests our knowledge of how the metabolic rate of fish varies. Fish are poikilotherms. They don't regulate their body temperature, thus have variable metabolic rates dependent on the temperature of their body at the time. Basal metabolic rate (BMR) in mammals is the rate of oxygen consumption at a resting state. The concept of BMR is not appropriate for fish because the metabolic rate in a resting fish will vary depending on the ambient temperature. Standard Metabolic Rate (SMR) is the metabolic benchmark in fish. It is the metabolic rate of a resting fish at a specified temperature in the middle of its normal range. Therefore a trout's SMR₁₅ would be the resting metabolic rate of a trout at 15^oC. There is natural law called Q₁₀ = 2: chemical reactions tend to double with every 10^o C increase in temperature of the reactants. In poikilotherms, this is translated into biochemical events and in turn into metabolism. The metabolic rates of fish roughly double with every 10^o C increase in temperature, except at the extreme ends of their temperature tolerance.