Evaluation of growth and energy storage as biological markers of DDT exposure in sailfin mollies Original Research Article

Direct and indirect measures of growth and energy storage were evaluated as indicators of subchronic 1,1,1-trichloro-2-(o-chlorophenyl)-2-(p-chlorophenyl)ethane (o,p′-DDT) exposure in juvenile sailfin mollies (Poecilia latipinna). Three-day-old mollies were exposed to 0, 1, 10, 25, 50, 75, and 100 μg/liter o,p′-DDT for 21 days. Tissue residues, percentage weight gain, RNA and DNA content, RNA:DNA ratio, percentage total lipid, percentage triglyceride, percentage total protein, and triglyceride:total lipid ratio were measured following exposure. Mortality was concentration and time dependent, with 100% mortality at 75 and 100 μg/liter. Among controls and remaining treatments, tissue residues (0.50 to 363 ng/mg dry wt), percentage weight gain (116 to 596%), percentage total lipid (2.84 to 4.33%), and percentage triglyceride (1.01 to 3.22%) were significantly different. Tissue residues were positively correlated with concentration, while percentage weight gain, percentage lipid, percentage triglyceride, and triglyceride:total lipid ratio were negatively correlated with concentration. Direct measures are likely to remain the method of choice for evaluating effects of toxicants on growth in laboratory exposures because of their relative simplicity and reliability. However, indirect measures of energy storage, such as triglyceride:total lipid ratio, rather than direct measures of various lipid fractions may be more reliable indicators of the energetic cost of toxicant stress.