Laboratory stocks of mosquitofish (Gambusia affinis) were acutely exposed to copper (0.16–0.24 mg/L) or cadmium (6.7–9.5 mg/L) for 48 h using a static renewal system. Allozyme genotypes at three polymorphic loci: phosphoglucomutase‒2 (PGM‒2), glucose phosphate isomerase‒2 (GPI‒2), and isocitrate dehydrogenase‒2 (ICD‒2) were resolved using a modified starch gel (13%) electrophoretic technique. Differential survivorship of allozyme genotypes was analyzed using a Wilcoxon matched pair signed‒rank test. Copper significantly (p < 0.05) decreased the overall survivorship of fish heterozygous at the GPI‒2 locus. The frequency of the (ab) genotype was significantly higher in the dead fraction of the test populations than in the surviving fraction. The frequencies of the (aa) genotype and the (a) allele at the ICD‒2 locus were significantly higher in female fish surviving exposure to copper than in nonsurviving females. The frequencies of the (bb) genotype and the (b) allele at the GPI‒2 locus were significantly higher in fish surviving exposure to cadmium than in nonsurvivors. These results indicate that some electrophoretically detectable allozymes are more sensitive than others to the toxic effects of environmental pollutants. This suggests that the genetic structure of natural populations should be considered for use as a biological monitor of environmental pollution.

Laboratory stocks of mosquitofish (Cumbusia uffinis) were acutely exposed to copper (0.16-0.24 mg/L) or cadmium (6.7-9.5 mg/L) for 48 h using a static renewal system. Allozyme genotypes at three polymorphic loci: phosphoglucomutase-2 (PGM-2), glucose phosphate isomerase-2 (GPI-2), and isocitrate dehydrogenase-2 (ICD-2) were resolved using a modified starch gel (13%) electrophoretic technique. Differential survivorship of allozyme genotypes was analyzed using a Wilcoxon matched pair signed-rank test. Copper significantly ( p < 0.05) decreased the overall survivorship of fish heterozygous at the GPI-2 locus. The frequency of the (ab) genotype was significantly higher in the dead fraction of the test populations than in the surviving fraction. The frequencies of the (aa) genotype and the (a) allele at the ICD-2 locus were significantly higher in female fish surviving exposure to copper than in nonsurviving females. The frequencies of the (bb) genotype and the (b) allele at the GPI-2 locus were significantly higher in fish surviving exposure to cadmium than in nonsurvivors. These results indicate that some electrophoretically detectable allozymes are more sensitive than others to the toxic effects of environmental pollutants. This suggests that the genetic structure of natural populations should be considered for use as a biological monitor of environmental pollution.

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The in vitro effects of copper and cadmium on fish enzyme activity were assayed by combining the metals with the biochemical stains used to resolve these enzyme systems on starch gels. The effects of copper and cadmium on the activity of PGM‐2, GPI‐2 and IDH‐2 enzymes in mosquitofish were assayed using stain‐metal mixtures containing 2.0 ml 0.1 m CuSO4 · 5H2O or 0.1 m CdSO4. Enzymes whose activities were effected by copper in this initial test were resolved using a series of stain‐metal mixtures containing copper at lower concentrations to determine effect threshold concentration ranges and to determine concentration ranges that might produce differential effects on activity among allozymes of a single protein. Interspecific differences in the effect of copper on the activity of PGM‐2 enzyme variants were examined for 17 fish species from seven locations. Copper was found to effect the activity of PGM‐2, GPI‐2, and IDH‐2 enzymes in mosquitofish and intraspecific and interspecific differences existed in the copper sensitivity of enzymes in a number of the fish species tested. Allozyme phenotypes at the PGM‐2 locus in mosquitofish observed on test gels (0.9 mg Cu/L) suggests that two isoalleles, one copper‐tolerant and one copper‐sensitive, are present at this locus.