Ichthyophthirius multifiliis (Fouquet): survival within immune juvenile carp, Cyprinus carpio L.

Abstract

Juvenile carp were immunised against Ichthyophthirius multifiliis by controlled exposure to theronts. Immediately following a potentially lethal challenge, immunised and non-immunised fish were injected intraperitoneally with either the corticosteroid triamcinolone acetonide (200μg g -1 body weight), saline or left untreated. More fish were similarly treated 1, 2, 3 or 4 days after challenge. Untreated immunised fish did not develop an infection, whereas 100% infection was recorded in untreated non-immunised fish and immunised and non-immunised fish treated with corticosteroid. Infection intensities decreased progressively in immunised fish treated with corticosteroid 1-4 days after challenge. Results indicate that theronts can enter immune fish which are immunosuppressed directly after challenge suggesting that pre-existing antibodies may only play a partial role in resistance. Immune suppression by corticosteroid 4 days after challenging immune fish did not lead to establishment of infection indicating that the cell mediated immune response effectively killed invading theronts within 4 days of entering the host.