The Toxicity of Bayluscide and TFM to Tubifex tubifex: Implications for Chemical Control of the Oligochaete Host of Myxobolus cerebralis, the Causative Agent of Whirling Disease

Abstract

Standard 24‐h toxicity tests were performed to determine the acute toxicity of Bayluscide (5,2′‐dichloro‐4′‐nitrosalicylanilide) and 3‐trifluoromethyl‐4‐nitrophenol (TFM) to two strains of the oligochaete worm Tubifex tubifex exposed and unexposed to Myxobolus cerebralis, the causative agent of whirling disease. In addition, microcosm trials were conducted to test the effect of three treatment levels of each chemical on the density of T. tubifex in an earthen hatchery pond. In the toxicity tests, worms that were susceptible to M. cerebralis infection were more sensitive to both chemicals than worms that were resistant to the parasite. The toxicity differences of exposed and unexposed worms within a lineage were not as great as those between lineages. Among worms that were susceptible to M. cerebralis, the concentrations of TFM that were lethal to 50% of the test organisms (LC50s) were 6.3 mg/L for worms that had been exposed to M. cerebralis myxospores and 7.3 mg/L for unexposed worms; for resistant worms, the corresponding LC50s were 8.2 and 7.7 mg/L. Among susceptible worms, the LC50s of Bayluscide were 0.060 mg/L for organisms exposed to M. cerebralis myxospores and 0.062 mg/L for unexposed organisms; resistant worms had LC50s of 0.096 and 0.106 mg/L. In the microcosm trials, Bayluscide treatments reduced worm densities by 73–82%, while the TFM treatments reduced worm densities by 34–88%. Given its rapid degradation, relatively selective toxicity, lower cost, and regulatory status, Bayluscide appears to be the best candidate for further study as a chemical control of the oligochaete host of the parasite that causes whirling disease in salmonid fishes.

Using Aquaculture as a Post-mining Land Use in West Virginia

“…These large-scale production facilities are operated by state and federal agencies to stock large areas for public recreational fishing. One problem with this type of facility is that animals in the source water are often carriers of serious diseases that are easily spread to other fish (Kowalski and Bergersen 2003;Mitchell 2002;Modin and Veek 2002). The concrete tanks are also costly to install, are not easily modified or moved, and time consuming to clean; in addition, the concrete erodes the soft fins of the fish.…”