امراض طفيلية في الاسماك

Fungal Diseases

Saprolegniasis
Etiology: saprolegnia parasitica-diclina compex. The predisposing factors include:


1. Handling.
2. Traumatic damage to the skin.
3. Overcrowded conditions.
4. Pollutions.
5. Bacterial or viral infections.
6. Additionally the stress induced by high (>18C.) water temperature
or low (<10C.) water temperature, also plays a role clinically.

Clinical signs:

Sapolegnia lesions are focal grey-white patches then
become dark grey or brown in color as the mycelium traps mud or silt.
Skin and gill lesions are most frequently observed. Gill infections
often arise from the mouth or branchial cavity. Infection of interal
organs (intestine) also occur. Infection normally occurs via breeches in
the epidermis or in the latter case via gut.

Histopathologically:


The fungus usually establish itself focally, invading
the stratum spongiosum of the epidermis and the spreads to the dermis
after causing erosion. Superficial invasion of the dermis lead to fluid
imbalance and peripheral circulatory failure [shock] due to inability to
maintain circulating blood volume. In H & E – stained sections of
skin infected with saprolegnia , numerous hyphae are seen on the skin
surface. Enmeshing cellular debris and material trapped from the water
by the hyphal strands. Beneath this surface mat of mycelium are areas of
degenerating tissue ranging from superficial dermal necrosis and odema
to deep myofibrillar necrosis and extensive hemorrhage. The majority of
lesion are, however, superficial, and often the only effect seen in
dermis is a water logging artifact rendered evident by variations in
staining affinity, the collagen fibers becoming more basophilic. There
is often only a slight inflammatory response but when concomitant
bacterial infection occurs, especially at higher temperature, a marked
inflammatory infiltrate is usually apparent. The fungal hyphae are
PAS-positive and easily demonstrated by silver impregnation methods,
such as Grocott's technique. They are branching, non septet and 20 um in
diameter.






Branchiomycosis


Also known as Gill rot and it characterized by areas of infective
necrosis in the gill due to intravascular growth of branchiomyces. The
causative fungi are B. sanguinis and B. demigrans.

Histologically:


Hyperplasia fusion of gill lamellae and areas of massive necrosis,
resulting from thrombosis of vessel by fungal hyphae, are seen together
with telangiectasis and vascular nerosis. B. sagnuinis does not grow
well outside blood vessel, unlike B. demigrans, while grows out through
the vessel wall as amass of hyphae . penetrating the necrotic tissues.
Affected fish may succumb as rapidly as 2 days after infection and
morbidity of up to 50 % may occur. Infection is probably by spores
librated from necrotic gill tissue but it's not known whether infection
occur directly though the gill or hematogenously after ingestion of
spores. It has been suggested that the reason for the localization in
gill vessels is that B. sanguinis can only develop in areas of high
oxygen tension. B. dimegrans has presumably a less demanding requirement
for oxygen. The disease was encouraged by water rich in organic
fertilizers. Alagl-blooms and temperature exceeding 20 C.



Ichthyosporidiosis = Icthyophoniasis


The disease is caused by Icthyophonous (I. hoferi) and a systemic
granulomatosis and affected both fresh-water and marine fish. Grossly,
the disease is characterized by roughened skin texture described as the (
sandpaper affect) occurring mainly on the latero-venteral tail region.
This effect is caused by the loss of epithelium over proliferating
dermal fungi granulomata. These are usually black in color and
approximately one mm in diameter and raised above the skin surface.
Further growth of the fungus causes local necrosis and result in
formation of either abscesses or ulcers. The internal organs (heart,
liver, muscle, kidney, spleen and brain) are also involved as evidenced
by the appearance of white nodules very similar to the granulomata of
tuberculosis. Infection occur through ingestion.




Ichthyobodo necatrix = Costia necator



1. This flagellate is the cause of costiasis.
2. Cosmopolitan in distribution and affects any fresh water fish.
3. Icthyobodo is a small parasite (10-15 um in length).
4. The free swimming stage is oval to kidney shaped with two pairs of flagella.
5. The attached stage of parasite is with out obvious flagella and penetrate epithelial cells with a type of holdfast organ.
6. There is hyperplasia of the malphigian cells and exhaustion of the
goblet cell in areas of parasite attachment, followed by spongiosis and
sloughing of epidermis leading to death by osmoregulatory failure.
7. Costiasis affect salmon culture, salmon is seawater and marine species.




Ichthyophthiriasis




1. Etiology is the trophozoite or feeding stage of icthyophthirius
multifillis and found within the epidermis of fresh water fish.
2. The disease is also called white spot disease
3. The disease is cosmopolitan in distribution and affects most species of fresh water fish.
4. Trophozoite live in the epidermis and it my reach to one 1 mm in
diameter and is as a characteristic white spot from which the disease
takes its name.
5. The trophozoite lies within cavity in which rotates, propelled by its uniform covering of cilia.
6. Icthyophthirius is easily recognized in skin scrapings by its size
and characterized by (horse shoe shaped) macronucleus. when nature
trophozoite.
7. When mature trophozoite break out through the epidermis and into
water this causes severe epithelial destruction leading to death of the
fish, probably due to osmoregulatory failure.
8. Ones free the parasite oocysts on a suitable substrate and divides to
produce up to 2000 elongate, ciliated to mites. Some 40 um in length.
These are release when cyst mature and they search out new hosts.





Chilodonella cyprini



1. This ciliated ectoparasite is the cause of chilodonelliasis.
2. The parasite has a flattened ovoid shape, is up to 80 um in length
and covered by rows of cilia which move it in a steady gliding manner
over the epithelial cells on which is actively feeds.
3. The parasite a serious pathogen in wintering carp.




Trichodinia piscium


1. This ciliate is the cause of trichodiniasis and found in fresh water fish.
2. The parasite possess an adhesion disc supplied with denticles.
3. It attacks the skin and the gills of most type of fish.
4. The disease has been reported in Iraq.


Protozoa of the alimentary canal






1. Hexamita ( 0ctomitus) : a small pyriform organism with three anterior
and one posterior pair of flagella. My cause catarrhal enteritis.
2. Coccidia: these are parasite of the gut. All have oocysts with four
sporocysts, each containing two sporozoites, with represent the stage of
the parasite infective to fish. Although there are exceptions, the
complete development of most fish coccidia is intracytoplasmic and takes
place within the same individual , i.e. endogenous development, and in
this they differ from coccidia of homeotherms, where sporogony takes
place externally. Development of gut coccidia takes place in the
epithelial and sub epithelial cells. Two best known are Eimeria sub
epithelial amd Eimeria carpelli, both of which causes serious disease in
carp culture. E. carpelli causes diffuse enteritis.
3. Cryptosporidia have been reported from the intestine of marine
tropical fish, where they cause digestive system disturbance and male
absorption leading to emaciation of the host.



Myxosoma cerebralis



The cause of whirling disease. Size of spores is
6.5-7 x 7.5-8 um. Infection occurs through spores when the water
temperature is 15 C. the trophozoitic penetrate the intestinal wall and
reach the blood and from here they arrive to cartilage of head and
vertebral column. They penetrate the cartilage , proliferate and damage
the organ of equilibrium.

Blood protozoa

1. Trypanosomes (trypanosome tineae, T. cyprinid).
2. Cryptobia (cryptobia cyprinid).