Gills of antarctic fish

We review the literature on the way the structure of icefish gills relates the physiology of these haemoglobin-less fishes. Vascular casting confirmed earlier reports that the only special feature of the gills is the large size of the blood vessels, especially the prominent and continuous marginal channels Isolated perfused gill arches were used to study the effects of changes in afferent and efferent pressure on gill resistance and tritiated water influx in Chionobathyscus dewitti. Increasing perfusion rate did not change gill resistance, but there were moderate proportional increases in water influx. Reducing efferent pressure increased gill resistance but did not affect water influx. In both C. dewitti and Cryodraco antarcticus gills perfused at constant flow rate, noradrenaline produced concentration-dependent decreases in gill resistance and, with high concentrations, increases in water influx. Fixation while perfusion continued was used to compare blood space dimensions in control, noradrenaline-treated and unperfused gills. Noradrenaline caused large increases in the thickness of the lamellar blood space and increased lamellar height, despite a greatly reduced afferent pressure. This suggests that modulation of pillar cell active tension might be involved in control of lamellar perfusion. The possible relationship between gill water fluxes and lamellar recruitment is discussed.