ABSTRACT: A fine structural investigation of the causative organisms of systemic granuloma in goldfish Carassius auratus revealed single-nucleate amoeboid organisms which were either intracellular, enclosed within a parasitophorous vacuole, or intercellular, embedded in an electron-dense matrix, presumably residues of defunct host cells. The nucleolemma-bound nucleus contained a large centrally positioned nucleolus. The cytoplasm contained ribosomal aggregates, endoplasmic reticulum and numerous adjunct thick-walled vesicles. Mitochondria were absent. Large cytoplasmic inclusions contained electron dense deposits. Additionally, cytoplasmic ribosome-rich bodies differentiated from the cytoplasm, segregating into an invagination of the organism's body wall and apparently were becoming confluent with the parasitophorous vacuole. The taxonomic and biological affinities of these organisms are discussed through comparison with similar Dermocystidium-like and amoeboid aetiological agents from fish.

KEY WORDS: Systemic granuloma . Goldfish . Fine structure . Amoeboids . Dermocystidium-like organisms

Published in DAO Vol. 26, No. 1 (1996) on July 18
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1996