Physiology of Finfish and Shellfish (2+1)

4.4.4. Acclimation to low oxygen levels

Many fast-swimming, active fish are quite sensitive to low oxygen in the water. If the fish has been kept in relatively oxygen-poor water, it becomes more tolerant to low levels of oxygen (Figure 6.3).

This improved tolerance is probably attributable to an enhancement of the ability to extract oxygen from the water. If there was a true increase in the ability of the tissues to tolerate anoxic conditions, a fish acclimated to low levels of oxygen could be expected to survive longer than a nonacclimated fish when placed in completely anaerobic conditions. There is no evidence of such a difference (Shepard 1955). The improved oxygen extraction could result from increased volume of water pumped over the gills, increased ability to remove oxygen from the water flowing over the gills, improved oxygen transport capacity in the blood, improved function of the heart, or any combination of these.