The objective of this project was to investigate two mechanisms that are commonly thought to be responsible for heavy metal resistance in aquatic invertebrates. Data were generated based on comparisons of growth and respiration experiments using instar III and IV Chironomus riparius under the influence of 0.0, 62.5, 125, 250, and 500 ppb zinc. Main comparisons were made between larvae that were cultured in clean water conditions and larvae from cultures that had been exposed to 10 ppb zinc for over a year and a half. Instar III larvae from clean water cultures showed significant reductions in growth and respiration rates when exposed to zinc concentrations of 62.5 ppb and greater; growth and respiration rates were significantly reduced in instar IV larvae at 125 and 62.5 ppb, respectively. Instar IV larvae from zinc cultures demonstrated increased tolerance to the metal while instar III larvae displayed no additional tolerance. To determine if the resistance was an acclimation or population adaptation phenomenon, additional growth and respiration experiments were conducted with F2 progeny of adults from zinc cultures that were reared in clean water. Results suggest that both acclimation and adaptation may be responsible for the increased tolerance to the metal. When growth and respiration data were converted to a caloric basis (calories respired per day and calories allocated as growth per day), non-tolerant individuals decreased the amount of energy assimilated per day and increased the proportion of energy respired vs. energy allocated to growth with increasing zinc concentration. Resistant individuals, as a result of changes in toxicological trends, demonstrated less dramatic versions of the previously described trends. / Master of Science