4.Discussion 4.1.Methodological constraints The metabolic data for fishes and cephalopods listed in tables 1-1and 1-2 were derived from experiments on unfed wild animals.Experiments in the absence of food are imperative to detennine the rates of respiration and ammonia excretion accurately without corrections for complex uptake/release of oxygen and ammonia by food organisms during experiments (lkeda et al,2000),but longer-term starvation of animals may influence their normal metabolism.specific dynamoc action (SDA) is a widespread phenomenon across diverse animals and is interpreted as the energy expended on ingestion,digestion,absorption and assimilation of food (Secor,2009).The magnitude and temporal variation of SDA are functions of feeding duration and meal size (Secor,2009). SDA accompanies an increase in ammonia excretion rates,but the pattern and magnitude differ greatly from those of respiration rates from one fish to the next (cf.review of Wood,2001).In a typical study on juvenile rainbow trout fed ad libitum, ammonia excretion increased 6-fold while respiration showed only a 1.7-fold increase in the 2 h after the cession of feeding (Alsop and Wood,1997).