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 to allow 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 the guppy (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.