A Study of the Effect of Temperature Changes On the Respiratory Pumps of the Rainbow Trout

Abstract

1. Trout subjected to changes in water temperature (1°/3 min.) between 15° and 30° C. showed a number of responses in their ventilation and cardiac mechanisms. 2. Ventilation rate increased slowly over the range 15°-21° C., but increased more rapidly at higher temperatures (21°-26°, Q₁₀=2.34; 26°-28°, Q₁₀=4.02). Cardiac frequency fell markedly about 26° C., and this bradycardia suggests that above this temperature the ventilation mechanism is inadequate to maintain a sufficient level of blood P_o . Possibly this insufficiency results from a failure of the pumping mechanism to increase or even maintain a large minute volume at high frequencies. 3. Pressure recordings indicate those parts of the ventilatory mechanism which are mainly involved in these responses. Increases in the buccal, opercular, and mean differential pressures indicated that the volume of water pumped across the gills increased during the initial stages of warming and only at higher temperatures did frequency become involved. Variability in the balance between the buccal and opercular pumps among individual trout becomes even more apparent under temperature stress, as in some cases the opercular pumps seem to be mainly involved in the increased ventilation but not always. 4. The action of the buccal and opercular pumps seems well co-ordinated, especially at intermediate temperatures, but serious uncouplings occur at higher temperatures as indicated by the shape of the pressure waveforms and especially the appearance of double reversals in the differential pressure curve. 5. The relationship between cardiac and ventilatory cycles was not studied in great detail, but there were certainly indications of changes in coupling. However, it was clear that the two rhythms do not always become phase-locked even at high temperatures. 6. The effect of changing temperature on the physical environment of the fish is discussed in relation to these observed responses.