An experiment was performed to evaluate the in vitro and in vivo efficacy of potassium permanganate (KMnO4) against Flavobacterium columnare. In vitro, F. columnare treated with KMnO4 at 2 mg/L for 8 h exhibited a 70% reduction in colony‐forming units (CFU). A minimum KMnO4 concentration of 10 mg/L was needed to inhibit bacterial growth. An acute and systemic experimental infection was produced in channel catfish Ictalurus punctatus by waterborne exposure to the bacteria after mechanical cutaneous abrasion to remove mucus and epithelium. At 22 h postchallenge, an 8‐h treatment with KMnO4 at 2.3 mg/L (2.0 mg/L above the average KMnO4 demand of 0.3 mg/L) was initiated. This did not reduce mortality in experimentally infected fish. The infection model utilized in the experiment was evaluated by examining the clinical signs and histopathology of infected fish. Fish in the model showed columnaris signs similar to those of a natural infection, including skin depigmentation and ulceration and gill necrosis. Histologically, the skin had severe ulcerative necrotizing dermatitis and the muscles had severe necrotizing myositis. The gills had severe multifocal necrotizing branchitis involving the lamellar and filament epithelium, pillar cells, and central venous sinus. Heavy bacterial aggregates of long rods were associated with the necrotic cellular debris. The identity of the bacteria isolated from the challenged fish was confirmed by polymerase chain reaction. The results suggest that KMnO4 is beneficial for reducing F. columnare load in the water column and possibly on fish, but the therapeutic value of KMnO4 is limited in fish with an acute and systemic columnaris infection. Further research is warranted to investigate the value of KMnO4 as a therapeutic agent for fish with a milder columnaris infection and as a treatment to prevent further spread of columnaris in a fish population.

The red-rim melania Melanoides tuberculata, a subtropical and tropical snail, is a nonindigenous species that has become established and is spreading in the United States. Of concern is the potential of the red-rim melania to displace native snail populations and to transmit trematodes that cause serious problems. One of these, a fish gill trematode, Centrocestus formosanus, has negatively affected U.S. commercial and wild fish stocks, including some endangered species. The snail has an operculum that can protect it from desiccation and can remain viable for days on dry fisheries equipment. Thus, contaminated fisheries equipment is suspected as one of the ways the snail is being moved from place to place. A study was conducted to find chemical treatments that would kill 100% of the red-rim melania. Thirteen different chemicals and chemical combinations were evaluated at different concentrations and for various exposure periods. Roccal-D-Plus, Hydrothol 191, niclosamide, and Virkon showed promise in 24-h exposures at concentrations of 20 mg/L active ingredient (AI), 80 mg/L AI, 2 mg/L, and 1,600 mg/L AI, respectively. Additionally, Roccal-D-Plus killed all snails exposed to 2,000 mg/L for 1 h and to 600 mg/L for 16 h. Roccal-D-Plus has a history of use as a disinfectant for fishery equipment.

The acute toxicity and highest nonlethal concentration of praziquantel (LC0) were determined in the laboratory for grass carp Ctenopharyngodon idella and golden shiner Notemigonus crysoleucas, two cyprinids known to harbor the Asian tapeworm Bothriocephalus acheilognathi. Praziquantel is an anthelmintic used to treat fish with tapeworms. The 24‐h and 96‐h LC50 values were 55.1 and 49.7 mg/L for golden shiners (1.3 g) and 63.4 and 60.6 mg/L for grass carp (9.1 g). The 24‐h and 96‐h LC0 values were 50.0 and 45.0 mg/L for golden shiners and 60.0 and 60.0 mg/L for grass carp.