Naturally occurring Trypanosoma granulosum infections in the European eel, Anguilla anguilla L. from County Mayo, western Ireland

• Published in: Journal of fish diseases 1997-09, Vol.20 (5), p.333-341
• Main Authors: Zintl, A, Poole, W R, Voorheis, H P, Holland, C V
• Format: Article
• Language: English
• Subjects: Anguilla anguilla; Trypanosoma granulosum
• ISSN: 0140-7775; 1365-2761
• DOI: 10.1046/j.1365-2761.1997.00306.x

Eels were sampled from three lake and two stream sites in the Burrishoole catchment, western Ireland, at bimonthly intervals; the eels were bled and released. Prevalence of Trypanosoma granulosum was determined using a haematocrit centrifuge technique and parasitaemia was estimated by counting trypanosomes in 30 fields (10 ocular × 10 objective) on Giemsa‐stained smears. Prevalence was consistently high in eels from the lake sites, but lower and more variable in the two stream sites. Parasitaemia was generally low and the distribution highly skewed. Individual eels carrying medium and high infections were most common in late summer and autumn. The size distribution of trypanosomes found in the blood was bimodal. Seasonal changes in trypanosome morph sizes indicated that parasitaemia did not increase immediately after infection, but was delayed until water temperatures increased during the summer months.