A Saprolegnia parasitica challenge system for rainbow trout: assessment of Pyceze as an anti-fungal agent for both fish and ova.

A reproducible Saprolegnia parasitica spore delivery system was developed and demonstrated to be effective in providing a sustained spore challenge for up to 10 d. Treatment of rainbow trout with slow-release intraperitoneal implants containing cortisol resulted in chronically elevated blood cortisol levels and rendered the fish susceptible to infection by S. parasitica when exposed to the spore challenge. Sham-implanted fish were not susceptible to infection. Bronopol (2-bromo-2-nitro-propane-1,3-diol), formulated as Pyceze, was effective in protecting predisposed fish from infection by S. parasitica when administered as a daily bath/flush treatment at concentrations of 15 mg l-1 and greater. Pyceze was also demonstrated to protect fertilised rainbow trout ova from S. parasitica challenge when administered as a daily bath/flush treatment at concentrations of between 30 and 100 mg l-1. Pyceze appears to qualify as a safe and effective replacement for malachite green and formalin in the prevention of fungal infections in the aquaculture environment.