ABSTRACT: 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-nitropropane-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.

KEY WORDS: Saprolegnia · Fungal infection · Salmonid · Bronopol · Pyceze · Cortisol

Published in DAO Vol. 36, No. 2 (1999) on May 12
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1999