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Dynamics of experimental production of Thelohanellus hovorkai (Myxozoa: Myxosporea) in fish and oligochaete alternate hosts
Author(s) -
Liyanage Y S,
Yokoyama H,
Wakabayashi H
Publication year - 2003
Publication title -
journal of fish diseases
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.819
H-Index - 85
eISSN - 1365-2761
pISSN - 0140-7775
DOI - 10.1046/j.1365-2761.2003.00492.x
Subject(s) - biology , cyprinus , carp , myxosporea , myxozoa , spore , gill , cyprinidae , common carp , zoology , anatomy , veterinary medicine , fish <actinopterygii> , microbiology and biotechnology , fishery , medicine
Abstract The dynamics of development and production of Thelohanellus hovorkai (Myxozoa) were examined to investigate factors inducing haemorrhagic thelohanellosis in carp, Cyprinus carpio L. Fresh actinospores of T. hovorkai were harvested from the oligochaete alternate host, Branchiura sowerbyi , and used for infection experiments with myxosporean‐free carp. Visualization of actinospores by fluorescent labelling revealed that sporoplasms penetrated the gill filaments of carp immersed in an actinospore suspension as early as 30 min post‐exposure (PE). Plasmodia of T. hovorkai developed in the connective tissues of various organs and matured 3–5 weeks PE; dispersion of myxospores from degenerate plasmodia occurred 5–7 weeks PE. Challenges with a high dose of actinospores (4.5 × 10 6 spores per fish) resulted in the onset of disease, which was more easily achieved by the oral intubation of actinospores than by immersion in an actinospore suspension. Actinosporean‐free B. sowerbyi were exposed to different densities of myxospores (10 4 –10 6 spores per oligochaete) and subsequently reared at different temperatures (15, 20, 25 °C). At 20 and 25 °C, actinospore releases were first detected 40–43 days PE, with multiple peaks of release (max. 7 × 10 5 actinospores day −1 ) during the next 60 days. We concluded that the developmental cycle of T. hovorkai was completed within 3–5 months at 20–25 °C, and that the ingestion of large numbers of actinospores orally, possibly by feeding on infected oligochaetes, resulted in a disease condition in carp.