The respiratory development of Atlantic salmon: II. Partitioning of oxygen uptake among gills, yolk sac and body surfaces

Abstract

During post-hatch development of Atlantic salmon (Salmo salar L.), O-2 uptake partitioning changes from primarily cutaneous to primarily branchial. Over 80% of post-hatch O-2 uptake was cutaneous, with the yolk sac responsible for 33% of total O-2 uptake. The well-vascularized yolk sac was a less effective gas exchanger than the unperfused skin of the body, suggesting that oxygen delivery is by direct diffusion to the tissues. Branchial O-2 uptake increased quickly as gill lamellae developed, contributing 60% of total O-2 uptake before the completion of yolk resorption (body mass 0.2 g) and increasing to 69-81% in fish weighing over 0.3 g. The area-specific O-2 uptake of the skin decreased through development as skin thickness increased, while that of the gills increased from 0.10 mu-g h-1 mm-2 to 0.23 mu-g h-1 mm-2. Partitioning of O-2 uptake of the skin and gills changed in concert with changes in the partitioning of the anatomical diffusion factor (ADF, mass-specific surface area per unit diffusion distance) between skin and gills, which changed from more than 95% to less than 10% cutaneous; thus, ADF is a useful rough indicator of oxygen uptake potential. Caution should be used in predicting oxygen uptake potential from ADF, however, because O-2 uptake per unit diffusion barrier of the yolk sac was less than half that of the general body surface, and O-2 uptake per unit diffusion barrier of the gills changed dramatically over development.