Acute Toxicity of Copper-Zinc Mixture to Rainbow Trout (Oncorhynchus mykiss) and its Impact on the Bacterial Flora of the Digestive Tract

Abstract

Investigations were carried out on acute toxicity of copper-zinc mixture to rainbow trout (Oncorhynchus mykiss) and on the abundance of bacteria in the digestive tract. The data obtained showed that the exposure duration evidently influenced the value of median acutely lethal concentration (LC50). The greatest differences were observed between 24-hour and 96-hour values, while 72-hour and 96-hour values were quite close. The abundance of total heterotrophic and proteolytic bacteria was greatest in controls and lowest in high concentrations mixture exposure. The abundance of total heterotrophic bacteria in the digestive tract from highest-exposure fish were two orders of magnitude lower compared to control fish. In these experiments, the cultivable total coliform bacterial densities actually increased following the addition of toxicant, possibly as a result of the release of organic carbon from poisoned copper-zinc sensitive organisms.