Acute Toxicity of Several Chemicals to the Oligochaete Dero digitata

Proliferative gill disease (PGD) is a serious problem in the farm‐raised channel catfish Ictalurus punctatus industry. Interrupting the life cycle of the sporozoan causative agent by eliminating Dero digitata worms from culture ponds would be one method of controlling PGD. Eight chemicals—sodium chloride, hydrogen peroxide, formalin, potassium permanganate, liquid copper sulfate, chloramine‐T, rotenone and Bayluscide—were tested for acute toxicity against D. digitata . Static, single compound acute toxicity tests were conducted using three replications (10 worm/replicate) of six chemical concentrations and a control. Spearman‐Karber analysis was used to calculate 24‐ and 48‐h LC50 concentrations based on active ingredient for each compound. Calculated 24‐h LC50 values were: sodium chloride 6,800 mg/L, hydrogen peroxide 13.2 μL/L, formalin 23.3 μL/L, potassium perrnanganate 5.7 mg/L, copper sulfate 7.6 mg/L, chloramine‐T 29.5 mg/L, rotenone 0.26 μL/L, and Bayluscide 0.24 mg/L. Formalin and hydrogen peroxide may be options for eliminating D. digitata populations in ponds with fish because their LC50 concentrations were consistent with safe concentrations for fish. Rotenone, Bayluscide, chloramine‐T, formalin, and potassium permanganate may be useful as a pond sterilization strategy by treating fingerling ponds prior to stocking fish each year. However, the presence of substrate and organic matter in ponds could impact the efficacy of the chemicals and D. digitata's response to treatment. Treatments should be further evaluated to determine field efficacy, procedures for use, and effects on cost of production.