Impact of Ontogenetic Changes in Branchial Morphology on Gill Function in Arapaima gigas

Abstract Soon after hatching, the osteoglossid fish Arapaima gigas undergoes a rapid transition from a water breather to an obligate air breather. This is followed by a gradual disappearance of gill lamellae, which leaves smooth filaments with a reduced branchial diffusion capacity due to loss of surface area, and a fourfold increase in diffusion distance. This study evaluated the effects these changes have on gill function by examining two size classes of fish that differ in gill morphology. In comparison to smaller fish (∼67.5 g), which still have lamellae, larger fish (∼724.2 g) without lamellae took up a slightly greater percentage of O2 across the gills (30.1% vs. 23.9%), which indicates that the morphological changes do not place limitations on O2 uptake in larger fish. Both size groups excreted similar percentages of CO2 across the gills (85%–90%). However, larger fish had higher blood Pco2 ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usep...