Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/6/2012
Publication Date: 4/3/2013
Citation: Farmer, B.D., Mitchell, A.J., Straus, D.L., Fuller, S.A., Bullard, S. 2013. Efficacy of bath treatments of formalin and copper sulfate on cultured white bass, Morone chrysops, concurrently infected by Onchocleidus mimus and Ichthyophthirius multifiliis. Journal of the World Aquaculture Society. 44(2):305-310. Interpretive Summary: Parasite infections on fishes are commonly encountered in the wild and in aquaculture. Juvenile fish are often plagued by such parasites, which can reduce potential growth and in worst cases cause death. Formalin and copper sulfate are both commonly recommended treatments to reduce the number of parasites in fish. However, these recommendations suggest a wide treatment range as a 'catchall', but little data has been generated on specific parasites or when using repeated treatments. Formalin and copper sulfate were tested on white bass infected with two common parasites (Ich and Gill flukes). Infected fish were treated with either formalin, copper sulfate, or no-treatment. The treatments were applied five times with a day separating each treatment. The infection intensity was measured by counting the number of parasites in a sample area. The infection intensity was used to measure how effective each application of the treatments was. The infection intensity counts were done after each treatment. Overall, formalin was more effective than copper sulfate at reducing the number of parasites on the fish. Formalin required three applications to reduce the number of parasite, whereas copper sulfate required five. The scale of reduction was also greater in formalin treated fish than with copper sulfate treated fish comparatively. Copper sulfate is less expensive than formalin however, and could still be used as long as five or more applications are used. These results should guide fish farmers in what chemical, dose and duration to use when encountering similar situations in the field. Proper treatment of fish parasites should lead to more efficient production and healthier fish.
Technical Abstract: Treatment efficacy of repeated 1 h baths of formalin (100 mg/L) or copper sulfate (CuSO4) (2.1 mg/L) were evaluated against concurrent infections of Onchocleidus mimus (Mueller, 1936; Monogenoidea: Ancyrocephalidae) and Ichthyophthirius multifiliis (Fouquet, 1876; Hymenostomatida: Ichthyopththiriidae) among naturally infected juvenile white bass, Morone chrysops (Rafinesque, 1820; Perciformes: Moronidae). Twenty juvenile white bass weighing approximately 10 g each were communally stocked into each of 12, 18 L aquaria (low volume flow-through) with air-stones and 10 L of 23 deg C filtered well water. Aquaria treatments were grouped as follows: four non-treated controls, four formalin-treated, and four CuSO4-treated. Formalin or CuSO4 was applied every-other-day during the 10-d study period for each aquarium, with controls receiving ambient water. Infection intensity was enumerated 20-24 h after each treatment cycle by counting individual O. mimus and I. multifiliis within a 2.25cm2 area of the second gill arch, comprising approximately 20 gill filaments, excised from two arbitrarily selected white bass per aquarium (n = 24 white bass each treatment cycle). Intensity (the number of parasites per sample area) of O. mimus was initially 4.7 (n = 15) and by day 10 was 0.5 (n = 40), 7.7 (n = 40), and 26.9 (n = 40) for formalin-treated, CuSO4-treated and control fish, respectively. Effectiveness for formalin and CuSO4 was 98.2% and 71.2%, respectively. Neither formalin nor CuSO4 treatment had any effect on intensity of infection by I. multifiliis. The formalin treatment regimen in the present study is proposed as an effective, inexpensive and simple ‘off-the-shelf’ method for killing ancyrocephalids and reducing gill-infecting monogenoid infrapopulation size to levels that are sub-clinical and likely non-pathogenic (i.e., below levels observed on asymptomatic infected fish).