Respiratory responses to hypoxia in fish

Abstract

Hypoxia is discussed in the widest sense, i.e., as the conditions under which cells suffer a lack of oxygen. From a consideration of the transfer of oxygen from the water to the cellular sites as a series of resistances, it is suggested that hypoxia can result from an increase in resistance anywhere along the chain, and possible types of hypoxia in fish are defined from this point of view.More detailed discussion is given in relation to (1) interference with gas transfer at the gill surface; (2) reduction in the blood O2 carrying capacity; (3) modifications in the cardiac and ventilatory frequencies and in the coupling between these two rhythms, and (4) the time course of the hypoxic stimulus.It is concluded that most of the increase in knowledge of hypoxia during the past ten years can be fitted into known theoretical frameworks, but there is still a great need for measurements of oxygen tension at all levels in the respiratory chain; attention needs to be directed to both diurnal and seasonal variations and especially to long-term changes in those environmental conditions which tend to result in hypoxia. © 1973 by the American Society of Zoologists.