Comparative efficacy of Pyceze® (bronopol) in controlling mortality of brown trout Salmo trutta eggs

The efficacy of Pyceze^® (Novartis Animal Vaccines) and Proxitane^® 0510 (Solvay Interox) in controlling the mortality of eggs was studied in brown trout Salmo trutta eggs under the usual incubation conditions in a hatchery affected by saprolegniosis. Eggs from eight spawnings and from two lines of brown trout were used. The cumulative mortality of eggs at the start of the eyed stage (M₁) and at hatching (M₂) was measured, as was the percentage of eggs with fungal infection at weekly intervals during the green stage. Mortality at M₂ with Pyceze^® ranged between 2.38% and 12.61% depending on the batch, with a mean of 6.10%. Mortality at M₂ with Proxitane^® varied between 5.83% and 43.86%, with a mean of 22.36%. Fungal colonization at the start of the eyed stage ranged between 0% and 0.15% when Pyceze^® was used and between 0.82% and 12.50% with Proxitane^®. Mortality rates were higher among those eggs left untreated. The results indicate that Pyceze^® (bronopol) is efficacious in controlling mortality caused by Saprolegnia spp. and other biological factors in fertilized brown trout eggs, as has been demonstrated previously in other salmonid species.