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 a nd demonstrated to be effective in providing a sustained spore challenge fo r up to 10 d. Treatment of rainbow trout with slow-release intraperitoneal implants containing cortisol resulted in chronically elevated blood cortiso l levels and rendered the fish susceptible to infection by S. parasitica wh en exposed to the spore challenge. Sham-implanted fish were not susceptible to infection. Bronopol (2-bromo-2-nitropropane-1,3-diol), formulated as Py ceze, was effective in protecting predisposed fish from infection by S, par asitica when administered as a daily bath/flush treatment at concentrations of 15 mg l(-1) and greater. Pyceze was also demonstrated to protect fertil ised 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 malachi te green and formalin in the prevention of fungal infections in the aquacul ture environment.