The Respiratory Development of Atlantic Salmon: II. Partitioning of Oxygen Uptake Among Gills, Yolk Sac and Body Surfaces Available to Purchase

During post-hatch development of Atlantic salmon (Salmo salar L.), O₂ uptake partitioning changes from primarily cutaneous to primarily branchial. Over 80 % of post-hatch O₂ uptake was cutaneous, with the yolk sac responsible for 33 % of total O₂ 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 O₂ uptake increased quickly as gill lamellae developed, contributing 60 % of total O₂ 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 O₂ uptake of the skin decreased through development as skin thickness increased, while that of the gills increased from 0.10 μg h⁻¹ mm⁻² to 0.23 μg h⁻¹ mm⁻².

Partitioning of O₂ 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 O₂ uptake per unit diffusion barrier of the yolk sac was less than half that of the general body surface, and O₂ uptake per unit diffusion barrier of the gills changed dramatically over development.