Transactions of the American Fisheries Society 114:423-429, 1985 ¸ Copyright by the AmericanFisheries Society 1985 Plasma Osmotic and Electrolyte Concentrations of Largemouth Bass from Some Acidic Florida Lakes 1 DANIEL E. CANFIELD, JR. AND MICHAEL J. MACEINA 2 Department of Fisheries andAquaculture FRANK G. NORDLIE Department of Zoology JEROME V. SHIREMAN Department of Fisheries andAquaculture University of Florida, Gainesville, Florida 32611 Abstract Five acidicclear(pH 3.7-4.9), three acidiccolored (pH 4.1-4.6), and three neutral(pH 6.9-7.3) north-central Florida lakeswere surveyed in 1983 to determineplasma osmoticand electrolyte concentrations, growth, and coefficients of condition for largemouth bass Micropterus salmoides floridanus. Plasma osmotic concentrations averaged greater than273 milliosmoles/kg in fishfrom acidiccolored and circumneutral lakes, but averaged less than 269 milliosmoles/kg in four of the acidicclearlakes. Growth and coefficients of conditionof largemouth bass > 305 mm total length in the acidic lakes weresignificantly lowerthan in the neutral lakes. Reductions in fish growth and condition,however,couldbe relatedto either acidic conditions or lake trophic status. Received April 22, 1984 Accepted February 28, 1985 A third to a half of Florida's 7,700 lakes may be sensitive to (unable to buffer) acidification from atmospheric deposition (Canfield 1983; Hendry and Brezonik 1984). Potential responses of the biota of these lakes to acidification are undetermined. Phytoplankton, zooplankton, and benthic invertebrate abundances are lower in acidic Florida lakes than in neutral ones (Cris- man and Brezonik 1980; Crisman et al. 1980; Beaver and Crisman 1981), but the acidic lakes also have lower phosphorus and nitrogen con- centrationsand this, rather than acidity, may be the primary constraint on biological production in such lakes (Canfield 1983). Acidification of northern lakes has causedfish mortality and re- productive failure (reviewed by Haines 1981), but fish survive and reproduce in some acidic Florida lakes at pH values equal to or below those of damaged ecosystems in the north (Can- field 1983). Little else, however, is known about the response of Florida fish to acidity. 1 Journal Series 5562 of the FloridaAgricultural Ex- periment Station. 2 Present address: Department of Wildlife andFish- eries Sciences, Texas A&M University, CollegeSta- tion, Texas 77843. In this paper, we examine plasma osmotic and electrolyte concentrations of naturally occurring Florida largemouthbassMicropterussalmoides floridanus from some acidic and circumneutral Florida lakes. Reductions in plasma electrolytes occurwhen fish are exposed to acidic stress (Lei- yestad and Muniz 1976; Wood and McDonald 1982). Loss of plasma electrolytes generally is accompaniedby a reduction in blood pH, an increase in hematocrit and hemoglobin, and a risein bloodviscosity and arterial pressure, which can lead to circulatory failure (Wood and McDonald 1982). We use plasma osmotic and electrolyte data, as well as data on growth and condition factors, to determine if existing acidic conditions cause physiological alterations in largemouth bass of Florida lakes. We also at- tempt a preliminary assessment of the potential vulnerability of Florida's largemouthbass pop- ulations to damageby acidification. Methods Eleven north-central Florida lakes were sam- pled once each for water chemistry and large- mouth bass between August 10 and November 7, 1983. The lakes were selected to represent three common Florida lake types: acidic clear; 423