The scaling and potential importance of cutaneous and branchial surfaces in respiratory gas exchange in young chinook salmon (Oncorhynchus tshawytscha

Measurements were made of the surface areas of the yolk sac, the fins, the head and trunk, the gill filaments and the gill lamellae of chinook salmon (Oncorhyn-chus tshawytscha Walbaum) weighing between 0.045 g (3.7 days posthatch) and 13.4g (180 days posthatch). Cutaneous surfaces initially accounted for the vast majority (approx. 96%) of the total area available for respiratory gas exchange. As fish grew, total branchial surface area expanded at a more rapid rate than cutaneous surface area and, thus, came to represent a progressively larger fraction of total surface area. The transition was relatively slow, however, and it was not until fish reached 2.5-4.0g that branchial area exceeded cutaneous area. Although some individual surfaces (e.g. the gill lamellae) followed rather complex patterns of expansion, the overall increase in respiratory surface area with tissue mass could be described reasonably well using only two equations; one for the period prior to complete yolk absorption (<0.4g) and one for the period following complete yolk absorption (>0.4g). Mass exponents for total surface area (b=0.85) and metabolic rate (£>=0.8-0.9) were not significantly different for the larger fish. In contrast, the mass exponent for total surface area (fo=0.39) was significantly less than that for metabolic rate (£>=0.9-1.0) for fish weighing less than 0.4 g. Changes in the relative efficiencies of the various exchange surfaces during the course of larval development probably account for this discrepancy