Effects of Water Acidity on Swimbladder Function and Swimming in the Fathead Minnow,Pimephales promelas

Abstract

Swimbladder function, buoyancy-related behavior, and swimming performance were examined in fathead minnows (Pimephales promelas) following chronic (>4 d) exposure to acid-treated water (pH 5.3). When denied surface access in still water, treated fish, unlike controls (pH 7.7), failed to increase buoyancy and standard volume over "access to air" levels and had significantly higher proportions of swimbladder CO2and O2. In current, treated fish reduced buoyancy over 48 h to a lesser extent than controls and were severely limited in their ability to increase internal pressure of swimbladder gases. pH significantly affected the maintenance of a minimum buoyancy over 32 d. Upon transfer from current to still water without access to air, the rate of buoyancy adjustment over 48 h was significantly slower in treated fish. With surface access, fish of both groups filled swimbladders within 6–12 h following removal from current; however, treated fish displayed significantly lower proportions of swimbladder CO2and O2at 12 and 24 h. Both groups of fish compensated hydrodynamically for insufficient static lift with higher frequencies of pectoral fin beats, treated fish having generally higher frequencies. Swimming performance was unaffected by water pH, but treated fish lost more weight than controls. We propose that impaired swimbladder function contributes to the elimination of fathead minnows from acidified environments.