SENSITIVITY OF BROOK TROUT TO LOW PH, LOW CALCIUM AND ELEVATED ALUMINUM CONCENTRATIONS DURING LABORATORY PULSE EXPOSURES

Yolk-sac larvae of brook trout (Salvelinus fontinalis) were exposed to four sequential low pH and calcium (Ca) pulses, nominally ranging from pH 6.5 to 4.0 in 0.5 pH unit increments, with and without 300-mu-g/l aluminium (Al) in 28-day toxicity tests. Calcium concentrations during the pulses varied from 0.5 to 1.3 mg/l. Swim-up larvae that had begun to feed were exposed to a single pulse of the same pH and Ca concentrations with 300-mu-g/l Al. The larvae were allowed to recover for 120-h at circumneutral pH and Ca concentration that varied from 2.1 to 3.3 mg/l after each pulse exposure. Effects of the pulse exposures on survival, growth, whole-body ion concentrations, and behavioral development were monitored. Mortality of larvae was significant in all low pH and Ca treatments with Al after the first pulse and after the first low pH and Ca pulse at pH 4.0. Growth was significantly reduced among larvae exposed to the low pH and Ca pulses at pH 4.0. In general, growth was most severely affected among larvae exposed to the low pH and Ca pulses with Al at pH 6.1 and lower. Relative to controls, the low pH and Ca pulse exposures with and without Al reduced whole-body Na+, Ca2+, K+, Mg2+, P, and Cl-. Whole-body Ca2+ was most severely reduced followed by Na+, K+, Cl-, P, and Mg2+. The pulse exposures also caused delayed development and significant reductions in swimming activity and feeding of the larvae. These results support field observations that cyclic pH and Ca depressions, and concurrent increases in Al concentrations may cause mortality and have other adverse effects on natural fish populations.