Biochemical composition, growth, and survival of the guppy, poecilia reticulata, during chronic sublethal exposure to cadmium

The survival, growth, and biochemical composition (protein, total lipid, total carbohydrate, free reducing sugars, RNA, DNA) of the guppy, Poecilia reticulata, exposed to low sublethal concentrations of cadmium throughout its life cycle (beginning with 5-day-old juveniles) was studied. The purpose was to get some insight on the cause of metal toxic effects and evaluate the utility of monitoring levels of biomolecules as bioindicators of chronic toxicant effects on fish. The LC50 (48 h) of cadmium for 5-day-old Poecilia was 56.77 mg/L. The median lethal times (LT50) of Poecilia exposed to low cadmium concentrations (0.5-5 mg/L) ranged from 7.65 to 72.51 days, and could be accurately predicted by the mortality observed after 20 days of exposure. The whole-body dry weight increase of cadmium-exposed guppies presented a decline from that of the controls. These declines were statistically significant after 20 days of exposure to concentrations higher than 1 mg/L and after 30 days to concentrations higher than 0.5 mg/L. The percentage content in RNA was the only variable from the studied macrobiomolecules that significantly decreased when guppies were exposed to Cd concentrations higher than 0.5 mg/L for 30 days. The same trend was apparent in the ratio RNA/DNA. However, the ratio protein/RNA/DNA significantly increased after 10 days of growth to 1.5 mg/L and after 20 days to concentrations higher than 0.5 mg/L, thus having a predictive value for early-life history stages of Poecilia exposed to Cd.