Acid-base balance in rainbow trout (Salmo gairdneri) subjected to acid stresses.

1. The respiratory properties of rainbow-trout blood were investigated in acid-stressed fish. In the first group acid was introduced into the bloodstream and in the second the carbon dioxide content of the ambient water was increased. 2. Initially the introduction of acid to the blood caused a decrease in blood pH and bicarbonate, and increases in oxygen uptake and ventilation volume. After 2-3 h these values had returned to the control levels. 3. Trout subjected to high ambient CO2 (about 10 mmHg) showed a decrease in blood pH while PCO2 and bicarbonate increased. After 8 h the trout began to show signs of compensation to the acidosis. 4. In each experiment the blood PO2 was little changed but blood O2 content was decreased and tended not to resume the control value even after several hours. 5. The results are discussed in terms of the various acid-base mechanisms thought to be available to the fish. These include branchial ion exchanges and the possible buffering roles of the extracellular and intracellular fluids.