Distribution of Oxygen Tension in the Blood and Water Along the Secondary Lamella of the Icefish Gill

1. Measurements of the gill area of two specimens of Chaenocephalus aceratus indicate that the resistance to water flow and overall exchange area are even less than had been supposed from work with other icefish. 2. Measurements of the oxygen tensions in the water and in blood entering and leaving the gills are used to determine the expected distribution of O2 tensions along a typical secondary lamella profile. The advantage of counter-current over co-current flow is clearly indicated by such analyses. 3. The absence of complications due to the O2 dissociation curve of the blood facilitates an extension of the analysis to different theoretical secondary lamellar profiles. It is shown that profiles similar to those usually found in fish gills are more efficient in maintaining O2 transfer. 4. Although the percentage utilization of O2 in the water passing through the gills is relatively low, the effectiveness of oxygenating the blood is very high in the icefish gill.