Protozoan parasitic diseases

Diagnosis method wet mount of skin or gills with parasite histopathology of skin or gills with parasite

Thecamoeba sp is an ectoparasite on the gills of rainbow trout, chinook salmon and coho salmon fry. Acanthomoeba is an ectoparasite on the European catfish. As the amoebae are associated with bacterial invasions, they are normally considered to be secondary, and to be feeding on the gill bacterial flora.

Velvet/rust disease Causitive agent-Oodinium sp-dinoflagellate parasites Symptoms- The infected fish exhibit Peppery coating Presence of minute yellowish brown markings on the body. clamped fins respiratory distress (breathing hard) The fish may show signs of irritation, shortage of breath

Contd… The trophont or feeding stage attaches to gills and skin and penetrates epithelial cells by means of its rhizoids. Treatment copper at 0.2 mg/l (0.2 ppm) to be repeated once in a few days if necessary. Acriflavin at 0.2% solution (1 ml/l). Salt treatment for a prolonged duration at 2 g/l can also be effective. Bath of 1% formalin dissolved in 10 l of tap water for about 30 minutes.

Cryptobia a biflagellated genus Attach in the gills of both fresh-water and marine fish This parasites do not damage host cells and has been suggested that Cryptobia may be a commensal

Costiasis Causitive agent-Ichthyobodo necatrix (= Costia necator), Ichthyobodo is a small parasite of 10–15 μmin length. The free-swimming stage is oval to kidney-shaped with two pairs of flagella of unequal length. The attached stage of Ichthyobodo is cuneiform (wedge shaped) in shape without obvious flagella and penetrates epithelial cells with a holdfast organ

Contd…... Symptoms Infected fish may appear grey in colour and will frequently turn on their flanks or ‘flash’ Costiasis may develop in salmon smolts in seawater Heavy mucus secretion by infected animal sometimes also referred to as “blue slime disease”. Treatment formaldehyde and malachite green but tougher than most protozoa. Prolonged KMnO₄ immersion and salt water bath (for freshwater fishes) could be used for control.

White spot disease Causitive agent-ciliated protozoan Ichthyophthirius multifiliis infect most species of freshwater fish and is cosmopolitan in distribution. Different life stages are- trophont (active feeding phase), tomont (cyst phase), theronts (free swimming phase) treatment Potassium permanganate can be applied at a concentration of 2 mg/l and three treatments are given 2 to 3 days apart. A short-term bath of 250 mg/l formalin for 30 to 60 minutes followed by a water change can also be effectively used to control l the infection.

Hole in the head disease (Head and Lateral Line Disease): Hexamita (Spironucleus), a flagellated protozoon cause severe gastrointestinal disease if present in large numbers Commonly affect the oscars and other cichlids Symptoms weight loss, decreased activity and refusal of food. Fish (angel fish)may lie horizontally on the surface of the water with the abdomen visibly distended. Treatment metronidazole (Flagyl) 25 ppm in water every other day for 3 days.

Guppy Killer Disease Causqative agent- free-living or parasitic ciliated protozoan pear-shaped protozoa The parasite is usually unaffected by parasiticides due to its ability to burrow deeply into skin of host. Best method of control is prevention through sound husbandry practices.  control  prevention through sound husbandry practices.

Peritrichate ciliates Epistylis sp. and Heteropolaria colisarum – commonly affect the freshwater fish This disease is usually not fatal in itself but may open the fish up to secondary bacterial disease. This infection could be easily treated with formaldehyde

Trichodinid peritrichs Ectoparasites of freshwater and marine fish Symptoms Infected fish has a greyish sheen due to excess mucus production and finally erosion of epithelium occurs. Trichodina is a disc-shaped ciliate protozoan found on the skin and gills of many fish. treatment Trichodinds are difficult to eradicate using chemical treatments – improvements in husbandry are essential.

Myxosporidia Parasites of skin, gills of marine and freshwater fish. Myxobolus cyprini Pernicious anaemia in carps Pararsites often concentrating in gills and destroying them leading to haemorrhagic anaemia and death. Myxobolus koi has been implicated in many outbreaks in South East Asia. Ski infections less pathogenic than gill infections but skin infections can decrease market value of fish Microsporidia - It is parasitic in fish skin and gills. eg. Glugea anomala.

Mircosporean They have unicellular spores with single or dinucleate sporoplasm and an extrusion apparatus always with a polar tube and cap. Obligatory intracellular parasites. eg. Glugea anomala, Plistophora sp.

Neon Tetra Disease Causitive agent-Plistophora sp. It is a microsporidian sporozoan parasite. It attacks the musculature of the affected fish. Infected muscle contains numerous sporoblasts containing spores High mortality is usually associated with this disease.  treatment Sporozoan infections are usually unresponsive to treatment and diseased fish should be removed from the tank

General Control measures Treatment depends on the lifecycle a) non-encysting and b) encysting Non-encysting – e.g. Trichodina and Ichthyobodo - can be treated by single short term drug application Encysting – e.g. Ichthyophthirius and Amyloodinium - need treatment directed against the free-swimming infective stage. Requires that chemicals be present in the medium for a long time. Standard Iodophor disinfectants kill these parasites.

Internal protozoan parasites Myxosoma cerebralis – affect the internal ear of the juveniles fishes and cause deformities during the development of the cranial cartilage. These are typical myxopsporedians Trophozoite stage is well developed and the main site of proliferation is brain including the auditory canal and also the gill arches. Fish swim in-tail chasing or whirling manner when fed or disturbed giving the disease name whirling disease.