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

Bronopol found effective against Sarolengnia fungus infection in brown trout

source: E Branson
Veterinary Record vol 151 no18, November 2 2002
starts p539, 3 pages long

Saprolegnia fungi are probably the pathogenic fungus species most commonly affecting fresh water fish. The fungi tend to affect fish that are already weakened by disease, injury or malnutrition. Handling may cause injury to skin, which can lead to infection, which gives the fish the appearance of having cotton wool patches. Malachite green, a teratogen and carcinogen, is traditionally used to treat salmonids, but no licensed treatment for UK fish farmers exists.

The trial sought to assess how useful bronopol could be in tackling a natural Saprolenia infection affecting rainbow trout. Bronopol is an enzyme inhibitor, and the formulation used came from Novartis Animal Vaccines. Eighty broodstock were used in the trial, carried out after handling to strip their eggs. The group was spilt into four groups of 20 fish each, moved to separate raceways from a common raceway. Two groups were treated with bronopol at 20mg/litre for 30 minutes per day, and two were given a placebo over 15 days.

The fish receiving bronopol showed zero infection level by the end of the trial, compared with 40% for one group and 70% for the other at the start, while the untreated fish showed an increased in infection from 35% to 55% in one group, and 45% to 74% in the other. Some infections in the untreated fish may have come from river water used in the raceways during the trial, while the treated fish were protected against reinfection. No adverse reactions to bronopol were apparent.