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Small
Subunit Ribosomal RNA Sequence Comparisons Demonstrate Link Between
Proliferative Gill Disease (PGD) and Hennequya N. Sp. in Channel Catfish L.M. Pote, L. Hanson, and R. Shivaji College of Veterinary
Medicine, Mississippi State University, Mississippi State, MS 39762 Proliferative gill disease (PGD) is associated with
major fish losses in commercial catfish.
Past research has indicated that this disease is linked to a myxozoan
parasite, Aurantiactinomyxon ictaluri.
Artificial infections with A. ictaluri, isolated from the
aquatic oligochaete, Dero digitata, have demonstrated a myxozoan stage
in the gills, identical to those seen in field infections. In several challenge studies, parasite-free
catfish were artificially infected with A. ictaluri. Seven days post-infection, fish from each
challenge group were necropsied and the typical PGD organisms were observed in
the gills. Three months post-infection,
the remaining fish were necropsied and a newly described cyst stage of PGD was
found, Henneguya ictaluri n. sp.
The H. ictaluri n. sp. spores were isolated and purified. DNA was isolated from these spores and the
rRNA gene was amplified using PCR primers specific for A. ictaluri. The gene sequence in the highly variable
region of these spores was found to be identical to the gene sequence of A.
ictaluri, the PGD stages found in the gills of the artificially infected
fish, and in naturally infected catfish. This is the first molecular evidence
that A. ictaluri, isolated from D. digitata, can infect catfish
and produce the typical PGD organisms in the gills and provides further proof
that the actinosporean, A. ictaluri, is actually a life stage of the
myxosporean Henneguya ictaluri n. sp.
Research supported by:
USDA/NRI: 96-02330. |