Properties of respiratory pigments in bimodal breathing animals: Air and water breathing by fish and crustaceans

Abstract

SYNOPSIS. Oxygen is nearly 30 times more available in air compared with water, whereas the carbon dioxide capacity of water is ̃28.5-fold greater than for oxygen, presenting bimodal breathing species with two very different respiratory milieus. The respiratory pigment plays a variable role in animals switching between the two media. In vertebrates the transition to air breathing involves two main strategies: a decrease in oxygen affinity and changes in other haematological parameters such as haematocrit. When appropriately analyzed, data reveal a decrease in blood oxygen affinity during transition to air. This may arise via differences in the intrinsic affinity as occurs in some amphibians, or be due to increasesin the organic phosphate: haemoglobin ratio when acclimating to air breathing. Adopting air breathing often promotes increased haematocrit. It is difficult to discern trends in haemocyanin functioning. Many but not all bimodal and air breathingspecies of crab contain haemocyanin with high affinity for oxygen. As with haemoglobin there is some tendency for blood haemocyanin concentration to increase with air breathing but bimodal species are quite variable in this regard. Different strategies for breathing air are employed by various bimodal crustaceans, some of which involve modulation of haemocyanin oxygenaffinity. The exact mechanisms are often species dependent and in all bimodal breathing organisms the role of the pigment is best appreciated when the demands of the local environment and the behaviour of the species are considered. © 1994 The American Society of Zoologists.