ABSTRACT
This chapter focuses on the respiratory and osmoregulatory functions of the gill and the trade-offs that exist in gill design—which has been defined as the osmo-respiratory compromise. In most fish, the gills are the only organ that receives the entire cardiac output, all of which must pass through the lamellae where it is potentially subjected to osmoregulatory perturbations associated with the environment. If the increase in ion losses during exercise does limit the metabolic scope of a fish, it would be expected that the iongas ratio is affected differently during exercise in active versus non-active species. The sheepshead minnow is one of the most stress tolerant fishes, surviving exposures to extreme salinities and/or temperatures. When fish are exposed to a new environmental condition, the level at which acclimation at the gill is observed is indicative of the process that may be most limited by that change.
