Effects of ration size and hypoxia on specific dynamic action in the cod

We present the first data on the effect of hypoxia on the specific dynamic action (SDA) in a teleost fish. Juvenile cod (Gadus morhua) were fed meals of 2.5% and 5% of their wet body mass (BM) in normoxia (19.8 kPa Po-2) and 5% BM in hypoxia (6.3 kPa Po-2). Reduced O-2 availability depressed the postprandial peaks of oxygen consumption, and to compensate for this, the total SDA duration lasted 212.0 +/- 20 h in hypoxia, compared with 95.1 +/- 25 h in normoxia. The percentage of energy associated with the meal digestion and assimilation (SDA coefficient) was equivalent between the different feeding rations but higher for fish exposed to hypoxia. Comparing peak oxygen consumption during the SDA course with maximum metabolic rates showed that food rations of 2.5% and 5% BM reduced the scope for activity by 40% and 55%, while ingestion of 5% BM in hypoxia occupied 69% of the aerobic scope, leaving little energy for other activities.