Interaction of Low pH and starvation on Body Weight and Composition of Young-of-Year Smallmouth Bass (Micropterus dolomieui)

Abstract

Effects of overwinter starvation on the body composition of young-of-year smallmouth bass (Micropterus dolomieui) were examined in laboratory and field studies. Interactive effects of starvation and low pH and body composition were examined in the laboratory. Changes in body composition associated with starvation were similar in laboratory and field studies: on a dry weight basis, the amount of water, ash, Ca, K, and Na increased progressively in both laboratory and wild fish. The amount of Cl per unit dry weight showed a moderate increase in the laboratory fish and a large decline in the wild fish. The effects on starving fish of 6-wk chronic exposures to nonlethal pH levels of 4.0-7.0 were examined in the laboratory. No pH effect was noted for levels greater than 5.0. Losses of water, ash, Ca, K, Cl, and Na increased as the pH declined. There was no consistent effect of pH on rate of loss of ash-free organic matter. The results suggested that starvation may reduce the tolerance of young smallmouth bass to low pH through progressive weakening of the osmoregulatory system.