Efficacy of bronopol against infection of rainbow trout (Oncorhynchus mykiss) with the fungus Saprolegnia species.

A trial was carried out to test the efficacy of bronopol against infection of rainbow trout broodstock with the fungus Saprolegnia species. Replicate groups of 20 fish were held in each of four raceways. Two groups were treated in baths containing 20 mg bronopol/litre for 30 minutes on 15 consecutive days, and the other groups were treated in a similar way with a placebo. In the treated groups the percentages of infected fish decreased during the trial from 70 per cent and 40 per cent to 0 per cent, whereas the percentages in the placebo groups increased from 45 to 74 per cent and from 35 to 55 per cent; the severity of the infection also increased in the placebo groups.