Partitioning of Oxygen Uptake between Cutaneous and Branchial Surfaces in Larval and Young Juvenile Chinook Salmon Oncorhynchus tshawytscha

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Abstract
Rates of O₂ uptake across the skin and across the gills of young chinook salmon Oncorhynchus tshawytscha weighing between 92 mg (shortly after hatch) and 1.1 g (well into the fry stage) were determined at 12° C with a two-chamber, closedsystem respirometer. Cutaneous uptake accounted for most of the O₂ consumed by newly hatched alevins (up to 84%). However, the branchial contribution increased rapidly during larval development, so that by the time alevins weighed about 281 mg (halfway through the alevin stage), only 50% of the total O₂, consumed was taken up across the skin. This trend continued; by the time the alevins began exogenous feeding (≈ 400 mg), cutaneous uptake had fallen to 40% of total O₂ consumption. The relative importance of the skin declined more slowly during the fry stage and appeared to stabilize at about 30% of total uptake. About half of the increase in the proportion of O₂, taken up across the gills was due to a relative increase in branchial surface area. The other half was due to an increase in the eficiency of branchial uptake as the fish matured. In newly hatched larvae, area-specific O₂ uptake across the gills was only slightly higher than that across the skin (10.1 vs. 7.5 μg · h⁻¹ · cm⁻²), whereas in a 1-g fry roughly six times as much O₂ per unit area was taken up across the gills as across the skin (60 vs. 9.6 μg · h⁻¹ · cm⁻²).

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