Ultrastructural analysis of Saprolegnia secondary zoospore cyst ornamentation from infected wild brown trout, Salmo trutta L., and river water indicates two distinct morphotypes amongst long‐spined isolates

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Abstract
Transmission electron microscopy was used to study the ornamentation of secondary cysts of 52 long‐spined Saprolegnia isolates, with and without oogonia, obtained from wild brown trout, Salmo trutta L., and water samples from various rivers in León (NW Spain). All the isolates had secondary cysts with long hooked hairs grouped in bundles, although significant individual differences were observed. There was a direct relationship between the number of bundles per cyst, the number of hairs per bundle and hair length. The isolates were classified into two morphological groups. The isolates with a higher number of bundles per cyst and bundles with a greater number and length of hairs, were included in cyst morphological Group I. The isolates with a smaller number and shorter length of these bundles and hairs were included in cyst morphological Group II. There was a relationship between the type of ornamentation of the secondary cysts and the origin of the isolates. The isolates from salmonids with saprolegniosis belonged to Group II, whereas most isolates from mucus and water belonged to Group I.