Evaluation of the toxicity of 8 insecticides in Salmo salar and the in vitro effects against the isopode parasite, Ceratothoa gaudichaudii

A comparison was carried out between trichlorfon (Neguvon), dichlorvos (Nuvan 1000), fenthion (Baytex), propoxur (Baygon), fenitrothion (Folithion), azamethiphos (Alfacron 50 WP), cyfluthrin (Solfac) and deltamethrin (K-Othrina EC) to evaluate the efficiency of commercial insecticides against Ceratothoa gaudichaudii and their safety to the host fish, Salmo salar. To evaluate the toxicity of the products to salmon, groups of 20 fish (average weight 100 g each) were mantained in tanks of sea-water and exposed to 3 concentrations of each product for a period of 60 min. Mortality was then determined. The surviving fish were changed into tanks with clean sea-water and checked after 24 h. A control group of 20 fish was mantained without treatment. Parasites were obtained from normal infected salmon and kept in sea-water at 15 °C. The efficiency of every product was tested at 3 concentrations and 2 exposure times in groups of 20 parasites of 2 sizes. Mortality of parasites was determined after 15 and 60 min of exposure to the products. The surviving parasites were then transferred to clean sea-water and observed 15, 20 and 24 h after treatment. Every tested concentration was repeated 3 times and one control group was mantained for each parasite size. Only trichlorfon, dichlorvos and fenthion were not toxic to fish at the tested concentrations. The first 2 products were 100% effective against both size of the parasite at concentrations of 300 and 3 ppm for 60 min of exposure, respectively.