DEET (N,N‐diethyl‐m‐toluamide) Toxicity to Channel Catfish, Ictalurus punctatus, Sac Fry

The combination of open facilities, moisture, and warm weather during channel catfish, Ictalurus punctatus, spawning season causes mosquito‐infestation problems. A common solution to mosquito problems in hatcheries is to use mosquito repellents applied to exposed skin and clothing. DEET (N,N‐diethyl‐m‐toluamide) is the active ingredient in most personal insect repellents. We determined the 24‐h acute toxicity of DEET to channel catfish fry. The toxicity test consisted of 10 sac fry in three replications of six concentrations (range: 157–478 μL/L) and a control. In addition to toxicity testing, a trial was conducted to determine the amount of active ingredient dispensed from two different applicators: a pump sprayer and an aerosol can. The 24‐h lethal concentration (LC₁₀) was 274 ppm, and the 24‐h LC₅₀ was 345 ppm. The concentration required to kill 50% of the organisms was above the 100 ppm threshold to be considered practically non‐toxic. The pump sprayer (98.11% active ingredient) dispensed 113.3 ± 0.57 mg (mean ± SEM) active ingredient per pump. The aerosol can (30% active ingredient) dispensed 526.8 ± 6.71 mg (mean ± standard error mean [SEM]) active ingredient per second. In hatcheries where air movement by fans is not sufficient to control mosquitoes, using insect repellent products containing DEET should be safe.