EXPOSURE METHODOLOGIES AND SYSTEMS FOR LONG-TERM CHEMICAL CARCINOGENICITY STUDIES WITH SMALL FISH SPECIES

Testing waterborne chemical carcinogens in fish models requires accurate, reliable, and reproducible exposures. Because carcinogenesis is a chronic toxicological process and is often associated with prolonged latency periods, systems must accommodate lengthy in-life test periods in which compound concentrations and environmental conditions must be carefully maintained. Here, systems and approaches are described for continuous long-term exposures with small fish species. The exposure system employed has enclosed chambers with internal walls of water-resistant materials, sliding doors for easy access, a water bath to maintain temperature, and exterior venting for air. Timer-controlled, overhead fluorescent lights provide a controlled photoperiod with dusk and dawn. Test aquaria sit within water baths that maintain temperature in the exposure tanks. Exhaust vents in the exposure chambers maintain a slightly negative air pressure in each system. Treatment media are provided by multicompartmented water partitioners and a series of liquid-dispensing injectors activated independently for each treatment to ensure accurate dosing. The exposure systems utilized are designed toallow for continuous exposure to constant concentrations of a test material with safeguards incorporated that limit the effect of events that may compromise the continuous operation of the system. This system has been used to date on two 28-day preliminary studies, a 13-month chronic carcinogenicity study with the medaka (Oryzias latipes), and a 16-month study with theguppy (Poecilia reticulata) with trichloropropane(TCP).Measured TCP concentrations from routine analyses conducted three times weekly during these studies resulted in accurate and consistent treatment concentrations.The system described is a state-of-the art system for prolonged, chronic aquatic exposures and has utility in investigating carcinogens and other types of aquatic toxicants that require a high level of hazard containment and dosing control.