209
Ichthyophonosis
The fungus Ichthyophonus hoferi Plehn and
Mulsow has been found embedded in the infected
fi sh tissues mostly as thick-walled, spherical,
multinucleate structure called a ‘resting spore’.
The cytoplasm of these resting spores gives a
positive PAS and Bauer reaction which indicates
that it contains glycogen, a common carbohydrate reserve of fungi. Moreover, strong PAS
reaction given by the wall of such spore indicates
its polysaccharide nature and, thus, confi rms the
notion that I. hoferi is a fungus.
Schaperclaus ( 1953 ), Reichenbach-Klinke
( 1956 ) and Reichenbach-Klinke and Elkan
( 1965 ) have indicated towards the possibility of
the presence of two forms of Ichthyophonus , i.e.
salmonoid form and aquarium-fi sh form, on the
basis of two different developmental patterns in
this genus (Prabhuji and Sinha 2009 ). Earlier as
well as the present-day studies, based on the histopathology of tumour tissues and of affected
vital organs of fi sh, have provided suffi cient data
to indicate the occurrence of a wide range of
polymorphism in I. hoferi . In this context the
most extensive studies, however, are the detailed
investigations by Sindermann and Scattergood
( 1954 ), Dorier and Degrange ( 1961 ), Amlacher
( 1965 ), Powles et al. ( 1968 ), Ruggieri et al.
( 1970 ), Sinha ( 1985 ), Prabhuji et al. ( 1988 ) and
Prabhuji and Sinha ( 2009 ).
Infection of the lateral musculature causing
the ‘sandpaper effect’ (roughening of the skin)
has been observed by Sindermann and
Scattergood ( 1954 ) in Atlantic herring. It may be
due to the formation of large number of papules
caused by proliferation of the fungus and the formation of necrotic areas in the sub-epidermal tissues. However, Srivastava et al. ( 1984 ), Sinha
( 1985 ) and Prabhuji and Sinha ( 2009 ) have found
roughening of skin, raised spots and irregular
tumourous galls on the skin of Carassius carassius. Reichenbach-Klinke ( 1956 ) has reported
blindness and exophthalmos of serranid fi sh from
the Mediterranean as a result of eye infection. He
(Reichenbach-Klinke 1960 ) has also reported the
cranial and dorsal ulceration.
Generally, no tissue or organ has been found
to be immune from infection by I. hoferi ; however, organs with a rich blood supply seem to be
more frequently affected. I. hoferi elicits a severe
focal granulomatous response resulting in cirrhosis and atrophy of the affected organs which can
eventually lead to replacement of most of the normal tissue by reticuloendothelial granulation tissue. According to Amlacher ( 1965 ), the fi rst
tissue response of the host consists of an increased
activity of the leucocytes, particularly the eosinophilic granulocytes. These leucocytes surround
the parasite and many of them are destroyed.
During this process, fi brocytes appear and eventually enclose (with one to several layers of long
cells) the resting spore of the parasite, the leucocytes and the necrotic debris. The result is a characteristic granuloma consisting of the central,
thick-walled, multinucleate resting spore surrounded by necrotic cells enclosed within a connective tissue capsule. In other cases the parasite
may be surrounded by long, radially arranged
cells or by epithelioid cells surrounded by a connective tissue capsule. Giant cells may also be
found, particularly in infected kidneys. Empty
resting spores, following germination and release
of the plasmodium or spores, may often become
infi ltrated with connective tissues.
There have been persistent suggestions in the
literature that natural I. hoferi infections of marine
fi sh may be initiated by ingestion of infected crustaceans, particularly the copepods (Jepps 1937 ;
Reichenbach-Klinke 1956 , Reichenbach-Klinke
and Elkan 1965 ; Sindermann and Scattergood
1954 ; Sindermann 1956 , 1958 ). However, the
defi nite evidences, in this context, are still lacking. Several experimental studies have shown that
the infection is initiated after ingestion of food
containing viable I. hoferi spores. Gustafson and
Rucker ( 1956 ) found that feeding fi sh viscera
from infected fi sh to rainbow trout, three species
of Pacifi c salmon and a cottid resulted in infection
of these fi shes, but they were unable to establish
infections in goldfi sh ( Carassius carassius ), guppies, squawfi sh or brown bullheads.
Sindermann ( 1958 ) also carried out infection
experiments with immature Atlantic herring and
12 Aquatic Oömycetology: A New Field of Futuristic Research
Ichthyophonosis
The fungus Ichthyophonus hoferi Plehn and
Mulsow has been found embedded in the infected
fi sh tissues mostly as thick-walled, spherical,
multinucleate structure called a ‘resting spore’.
The cytoplasm of these resting spores gives a
positive PAS and Bauer reaction which indicates
that it contains glycogen, a common carbohydrate reserve of fungi. Moreover, strong PAS
reaction given by the wall of such spore indicates
its polysaccharide nature and, thus, confi rms the
notion that I. hoferi is a fungus.
Schaperclaus ( 1953 ), Reichenbach-Klinke
( 1956 ) and Reichenbach-Klinke and Elkan
( 1965 ) have indicated towards the possibility of
the presence of two forms of Ichthyophonus , i.e.
salmonoid form and aquarium-fi sh form, on the
basis of two different developmental patterns in
this genus (Prabhuji and Sinha 2009 ). Earlier as
well as the present-day studies, based on the histopathology of tumour tissues and of affected
vital organs of fi sh, have provided suffi cient data
to indicate the occurrence of a wide range of
polymorphism in I. hoferi . In this context the
most extensive studies, however, are the detailed
investigations by Sindermann and Scattergood
( 1954 ), Dorier and Degrange ( 1961 ), Amlacher
( 1965 ), Powles et al. ( 1968 ), Ruggieri et al.
( 1970 ), Sinha ( 1985 ), Prabhuji et al. ( 1988 ) and
Prabhuji and Sinha ( 2009 ).
Infection of the lateral musculature causing
the ‘sandpaper effect’ (roughening of the skin)
has been observed by Sindermann and
Scattergood ( 1954 ) in Atlantic herring. It may be
due to the formation of large number of papules
caused by proliferation of the fungus and the formation of necrotic areas in the sub-epidermal tissues. However, Srivastava et al. ( 1984 ), Sinha
( 1985 ) and Prabhuji and Sinha ( 2009 ) have found
roughening of skin, raised spots and irregular
tumourous galls on the skin of Carassius carassius. Reichenbach-Klinke ( 1956 ) has reported
blindness and exophthalmos of serranid fi sh from
the Mediterranean as a result of eye infection. He
(Reichenbach-Klinke 1960 ) has also reported the
cranial and dorsal ulceration.
Generally, no tissue or organ has been found
to be immune from infection by I. hoferi ; however, organs with a rich blood supply seem to be
more frequently affected. I. hoferi elicits a severe
focal granulomatous response resulting in cirrhosis and atrophy of the affected organs which can
eventually lead to replacement of most of the normal tissue by reticuloendothelial granulation tissue. According to Amlacher ( 1965 ), the fi rst
tissue response of the host consists of an increased
activity of the leucocytes, particularly the eosinophilic granulocytes. These leucocytes surround
the parasite and many of them are destroyed.
During this process, fi brocytes appear and eventually enclose (with one to several layers of long
cells) the resting spore of the parasite, the leucocytes and the necrotic debris. The result is a characteristic granuloma consisting of the central,
thick-walled, multinucleate resting spore surrounded by necrotic cells enclosed within a connective tissue capsule. In other cases the parasite
may be surrounded by long, radially arranged
cells or by epithelioid cells surrounded by a connective tissue capsule. Giant cells may also be
found, particularly in infected kidneys. Empty
resting spores, following germination and release
of the plasmodium or spores, may often become
infi ltrated with connective tissues.
There have been persistent suggestions in the
literature that natural I. hoferi infections of marine
fi sh may be initiated by ingestion of infected crustaceans, particularly the copepods (Jepps 1937 ;
Reichenbach-Klinke 1956 , Reichenbach-Klinke
and Elkan 1965 ; Sindermann and Scattergood
1954 ; Sindermann 1956 , 1958 ). However, the
defi nite evidences, in this context, are still lacking. Several experimental studies have shown that
the infection is initiated after ingestion of food
containing viable I. hoferi spores. Gustafson and
Rucker ( 1956 ) found that feeding fi sh viscera
from infected fi sh to rainbow trout, three species
of Pacifi c salmon and a cottid resulted in infection
of these fi shes, but they were unable to establish
infections in goldfi sh ( Carassius carassius ), guppies, squawfi sh or brown bullheads.
Sindermann ( 1958 ) also carried out infection
experiments with immature Atlantic herring and
12 Aquatic Oömycetology: A New Field of Futuristic Research