Technical Abstract: In the spring when channel catfish, Ictalurus punctatus, hatcheries are in full operation, the associated moisture and warm temperatures provide a haven for mosquitoes. Large swarms of biting mosquitoes in a hatchery can make the tedious work of egg-picking (i.e., removing dead and fungus-infested eggs from egg masses) and feeding fry almost unbearable. Besides causing undesirable working conditions—for workers sensitive to mosquito bites, blisters, bruises, or large inflammatory reactions can occur—mosquitoes also harbor viruses or other diseases that can be transmitted to humans, including West Nile Virus. In many hatcheries, a few strategically placed fans for air movement can remediate the mosquito problem. However, during certain years and in some hatcheries, additional control is needed. Several chemical repellents are available for mosquito control, but their toxicity to catfish fry is not known. The objective of this study was to screen chemical mosquito repellents and a common synergist for their toxicity to hannel catfish sac fry.