ABSTRACT
Gas exchange, however, is required right from the start of development of the fertilised egg. This implies that gas exchange initially must occur through the cellular integument of the developing embryo, having traversed the boundary layer, chorion and perivitelline fluids of the embryo, or the surface epithelium of the hatched larva. The influence of oxygen deficiency and also of temperature on gas exchange is discussed. Finally, the development of ventilatory control and the response to hypoxic conditions are considered. Considering embryonic and larval gas exchange, convective gas transport in the blood stream can only occur after the onset of cardiac activity, establishing blood flow in the circulatory system. Gas exchange of the egg and the developing embryo is via cutaneous gas exchange. Gills, and especially the secondary lamellae, the main gas exchanger of adult fish, can only contribute to gas exchange once they have developed.
