Branchial Acid and Ammonia Fluxes in Response to Alkalosis and Acidosis in Two Marine Teleosts: Coho Salmon (Oncorhynchus kisutch) and Starry Flounder (Platichthys stellatus)

Metabolic acidosis, whether endogenous (exhaustive exercise) or exogenous (ammonium sulfate infusion), had qualitatively similar effects on net ammonia flux (JₙₑₜAm) and net transfer of acid-base equivalents (Jₙₑₜ^H⁺) in salmon and flounder. Intravascular infusion of ³⁵S-labeled ammonium sulfate resulted in a rapid and large increase in JₙₑₜAm in both ospecies, although JₙₑₜAm was about three times greater in salmon than in flounder. Rates of 35SO4 clearance in salmon were 50-60 times those in flounder, and 35SO4 was distributed in a much smaller space than in flounder. Exhaustive exercise also led to increases in both JₙₑₜAm and Jₙₑₜ^H⁺ and again fluxes were 2-3 times greater in salmon than flounder. In both treatments the blood acid-base disturbance was corrected more rapidly in salmon than in flounder. Metabolic alkalosis (sodium lactate infusion) also elicited qualitatively different responses from salmon and flounder. In salmon, there was a net base excretion (i. e., a positive Jₙₑₜ^H⁺), and, except for a slight, although significant, reduction 4-8 h after infusion, JₙₑₜAm was unchanged. In contrast, Jₙₑₜ^H⁺ remained unchanged in flounder, despite a nearly 50% reduction in JₙₑₜAm, which persisted for 8 h after infusion. As was the case for acidosis, the blood acid-base disturbance was corrected more rapidly in salmon than in flounder. The different responses may be related to differences in the morphology (e.g., surface area) and/or permeability characteristics of the gills.