DIRECT CALORIMETRY OF AQUATIC ANIMALS - EFFECTS OF THE COMBINATION OFACIDIFICATION AND HYPOXIA ON THE METABOLIC-RATE OF FISH

The results of acidification on the metabolic rate of tilapia (Oreochr omis mossambicus Peters) were studied in a differential 1-liter flow-t hrough microcalorimeter (Setaram GF 108). After three days at pH 7.6 a t normoxic conditions, the pH was slowly reduced to pH 4.0 at an acidi fication rate of 3.6 pH units over 240 min. Acidification during normo xia had no significant effects on the heat production (Q over dot), th e oxygen consumption (V over dot O-2) and the oxycaloric equivalent. F urthermore, we investigated whether the combination of hypoxia and aci dification works synergistically. Fish were exposed to a graded hypoxi a load of respectively 40% air saturation (AS), 25% AS, 15% AS and 5% AS, 8 h per level, in combination with acidification at pH 4.0. No sup port for a synergism was found in this study. All tilapia survived sev ere hypoxia (5% AS) in combination with acidification (pH 4.0) due to a metabolic depression.