parasite is mobile and does not attach permanently, but
irritation of the gill lamellae can cause respiratory distress
associated with excessive mucous. Histologically, mild
hyperplasia and epithelial sloughing is observed. The differential diagnosis would be problems with water quality
Trichodinids are round and disc shaped parasites
(Figs. 8.9 and 8.10). T. truttae is distinguished from other
fresh water species by its large body diameter of
114–179 μm, as well as the presence of radial ridges on the
oral surface and two markedly different lengths of cilia. The
oral-aboral axis is shortened with a prominent basal disc
(usually at the aboral pole).
Diagnosis is achieved by examining wet mounts from gill
or the body surface, with demonstration of a cup or dome
shaped organisms that move in a characteristic circular manner with a spiral of oral cilia at the anterior pole. The diagnosis
of trichodinids can be completed with histological sections
and morphology of the denticles in the adhesive discs.
8.2.5 Scyphidia (Riboscyphidia, Ambiphyra)
Scyphidia, Riboscyphidia and Ambiphyra are considered
as synonyms, although there is little consensus about their
‘correct’ taxonomical status. These ectocommensal organisms are sessile peritrichs and their occurrence on freshwater
fish can result in small wounds through the release of ‘protein
enzymes’, opening areas for bacterial infection. Mortality has
been associated with chronic infections of the gills by
Ambiphyra, inducing mechanical blockage of the respiratory
epithelium. Diagnosis is dependent upon identification from
skin or gill scrapings or histopathology (Fig. 8.11).
8.3
Mesomycetozoea
8.3.1 Ichthyophonus hoferi
Ichthyophonus hoferi causes a granulomatous systemic
disease primarily in marine fish, with several well reported
epizootics occurring in wildfish including rainbow trout and
Chinook salmon. Farmed salmonids are susceptible to infection resulting in poor growth rates. Clinical signs and pathology vary, but largely dependent upon the organs affected and
the degree of infection. Behavioural anomalies, including
lethargy and uncoordinated swimming movements, have
been reported in salmon, particularly, where infection is
located in the central nervous system.
A reservoir is believed to be present in marine fish and the
common route of infection for farmed rainbow trout is probably through the ingestion of infected material. Ingested multinucleate spherical bodies will germinate and penetrate the
gastric mucosa, entering the bloodstream and are thereby,
spreading to several organs where secondary cysts are formed.
Fig. 8.9 Cross section showing Trichodina sp. from gill of Atlantic
salmon. High power
Fig. 8.10 Aboral view of Trichodina sp. Normarski interference contrast. High power
Fig. 8.11 Riboscyphidia sp. attached to lamellae of Atlantic salmon parr
112
8 Protists
irritation of the gill lamellae can cause respiratory distress
associated with excessive mucous. Histologically, mild
hyperplasia and epithelial sloughing is observed. The differential diagnosis would be problems with water quality
Trichodinids are round and disc shaped parasites
(Figs. 8.9 and 8.10). T. truttae is distinguished from other
fresh water species by its large body diameter of
114–179 μm, as well as the presence of radial ridges on the
oral surface and two markedly different lengths of cilia. The
oral-aboral axis is shortened with a prominent basal disc
(usually at the aboral pole).
Diagnosis is achieved by examining wet mounts from gill
or the body surface, with demonstration of a cup or dome
shaped organisms that move in a characteristic circular manner with a spiral of oral cilia at the anterior pole. The diagnosis
of trichodinids can be completed with histological sections
and morphology of the denticles in the adhesive discs.
8.2.5 Scyphidia (Riboscyphidia, Ambiphyra)
Scyphidia, Riboscyphidia and Ambiphyra are considered
as synonyms, although there is little consensus about their
‘correct’ taxonomical status. These ectocommensal organisms are sessile peritrichs and their occurrence on freshwater
fish can result in small wounds through the release of ‘protein
enzymes’, opening areas for bacterial infection. Mortality has
been associated with chronic infections of the gills by
Ambiphyra, inducing mechanical blockage of the respiratory
epithelium. Diagnosis is dependent upon identification from
skin or gill scrapings or histopathology (Fig. 8.11).
8.3
Mesomycetozoea
8.3.1 Ichthyophonus hoferi
Ichthyophonus hoferi causes a granulomatous systemic
disease primarily in marine fish, with several well reported
epizootics occurring in wildfish including rainbow trout and
Chinook salmon. Farmed salmonids are susceptible to infection resulting in poor growth rates. Clinical signs and pathology vary, but largely dependent upon the organs affected and
the degree of infection. Behavioural anomalies, including
lethargy and uncoordinated swimming movements, have
been reported in salmon, particularly, where infection is
located in the central nervous system.
A reservoir is believed to be present in marine fish and the
common route of infection for farmed rainbow trout is probably through the ingestion of infected material. Ingested multinucleate spherical bodies will germinate and penetrate the
gastric mucosa, entering the bloodstream and are thereby,
spreading to several organs where secondary cysts are formed.
Fig. 8.9 Cross section showing Trichodina sp. from gill of Atlantic
salmon. High power
Fig. 8.10 Aboral view of Trichodina sp. Normarski interference contrast. High power
Fig. 8.11 Riboscyphidia sp. attached to lamellae of Atlantic salmon parr
112
8 Protists