DIFFERENT TYPES OF FISH DISEASES Like humans and other animals, fish suffer from diseases and parasites. Fish defences against disease are specific and nonspecific. Non-specific defences include skin and scales, as well as the mucus layer secreted by the epidermis that traps microorganisms and inhibits their growth. If pathogens breach these defences, fish can develop inflammatory responses that increase the flow of blood to infected areas and deliver white blood cells that attempt to destroy the pathogens. There are different types of fish diseases some of them are- bacterial, protozoan, fungal etc. Bacterial diseases in fish 1) Furunculosis 2) Columnaris 3) Dropsy 4) Vibriosis 5) Tuberculosis 6) Bacterial gill disease 7) Fin rot/tail rot COMMON SYMPTOMS AND CAUSE COMMON SYMPTOMS CAUSE lethargic swimming Poor water quality Loss of appetite Fluctuation in temperature Respiratory distress Improper nutrition Jumping from the water Access waste deposition Colour of gill changed Fins become frayed Furunculosis Causative agent - Aeromonas salmonicida • Furunculosis is highly contagious disease that affects fish of all ages. • The infection causes high mortality in salmonids, though some other species of fish are affected. • Horizontal transmission occurs via the water column, but also through direct fish-to-fish contact and animal vectors. Pathological sign • Furuncles (or boils) involving skin and/or muscle progressing to lesions. • Haemorrhages on the skin, mouth and fin bases. • Darkening of body colour and pale gills. • Bloody discharge from nares and/or vent. • Stomach filled with mucus, blood. Treatment • Treatment is done by removing the severely infected fishes from the pond and by supplying food containing antibiotics like introfurans or sulphonamids etc. Columnaris (cotton mouth) Causative Organism: Flexibacter columnaris/Chondrococcus columnaris • Often mistaken for a fungal infection because of its mold-like lesions. • Columnaris is a common bacterial infection in aquarium fish, particularly livebearing fish and catfish. Symptoms • White spots on mouth, edges of scales, and fins. • Fins disintegrate beginning at the edges. • Saddleback' lesion near the dorsal fin. Treatment- • Normally used antibiotics include the chloramphenicol ( 10 ppm. repeated at 2-5 days interval ) and furance ( o.1 – 0.3 ppm ) in which the infected fishes with cotton mouth disease are kept for a long time bath. Infectious Dropsy Causative agent- Pseudomonas punctata • Dropsy is an old medical term that was once used to describe swelling due to accumulation of fluids in the tissues or body cavities, such as the abdomen. Fish suffering from Dropsy often have a hugely swollen belly. • It was the most feared disease in carp culture Symptoms • Swollen belly. • Scales stand out. • Eyes bulge. • Internal organs are affected, most notably the liver and kidneys. • Fish hangs near the surface. Treatment- • The infected fishes may be cured by a two minutes dip in 5 mg / KMnO4 sol. Vibriosis Causative agent – Vibrio anguillarum • This is comma shaped bacterium. • It enters the animal via their food and attacks the gastrointestinal tract. • Found in all species in saltwater • It multiplies in the skin of salmonids, but the toxins produced act on the circulating blood cells causing severe anaemia. • This disease occurs more than readily at temperture above 11°c. Symptoms • Large bright colour body lesions in the skin and muscles. • Gills may bleed with slightly pressure. • Inflammation of intestinal tract. • Eye problems with cloudy eye, leading to pop- eye and finally eye loss. Treatment- • Dip treatment in copper sulphate sol. and application of antibiotics with artificial food may be considered as curative measures for vibrosis Tuberculosis Causative agent- Mycobactrium piscium. • A bacterium closely related to Mycobacterium tuberculosis called Mycobacterium piscium can be present in wild caught as well as captive bred fish and stay lurking in our aquariums without us ever realizing it. • Fish can be treated with the same drugs as humans get when they become infected by Mycobacterium piscium, e.g. Kanamycin. SYMPTOMS • Fin rot , waxy coat on body , ulcer on body. • Nodules in the internal organs • loss appetite • Loss body weight • Loss of scales • Loss of colour Treatment- • Dip treatment for one minute in 1 : 2000 copper sulphate sol. for 3-4 days may be useful. Bacterial gill disease Causative agent- Myxobacteria • The colonization of damaged gills by these organisms in the condition known as “BACTERIAL GILL DISEASE” • This reduces the ability of the gills to supply oxygen to the blood and results in mortality if left unchecked. Symptoms • Swelling in gill lamellae. • Change in gill colour. Treatment- • Application of antibiotics like neomycin chloramphenicol etc. may be useful in treatment of bacterial gill disease in fishes . Fin rot / tail rot Causative agent- Myxobacteria • Fin Rot is one of the most common. • It is caused by several types of bacteria and often occurs concurrently with other diseases. SYMPTOMS • Fin edges turn white • Fins fray • Bases of fins inflamed • Entire fin may rot away Treatment- • Move sick fish to a hospital tank. • Feed fresh high quality foods. • Treat with antibiotics(MARACYN-2, a ten day course is ideal for ensuring the infection is eradicated) Protozoan DiseasesVelvet/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. • 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. Costiasis or Ichthyobodiasis 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. 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 /Ich 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. 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 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. FUNGAL DISEASE Cotton wool disease Causative agent – Saprolegnia • opportunistic pathogenic fungi affecting tropical fishes and fish eggs Symptoms • greyish white, cotton-like growths on the skin, gills, eyes, or fins that may invade deeper tissues of the body. preventive measures • removal of predisposing causes, e.g. inadequate sanitation, • excessive chemical treatment, or the presence of dead, infected fish and decaying organic material. Ichthyophonus hoferi • This fungus causes an internal infection and is generally chronic and progressive. Preventive measures • removing infected fish and avoiding feeding raw fish products. • Iodophors of varying iodine concentrations are used to prevent mycotic infections of nonfood-fish eggs, which can be disinfected by a 100 ppm iodine bath for 10-15 min. • Formaldehyde, up to 2,000 ppm for 15 min, can be used to treat eggs Epizootic Ulcerative Syndrome (EUS) • Cause damage to a wide variety of fishes (most affected are murrels) but chineese carp and tilapia relatively resistant Causitive agent-Aphanomyces invadans. • Infection starts as a red spot in the skin then it eventually becomes an ulcer and finally resulting in erosion of ulcerative area. Disgnosis:-Grocott’s stain is used for fungal staining. It gives black colouration in the fungal hyphae. A. invadans has the ability of penetrating the body of the fish using the proteolytic enzyme It causes mortality by two means • (i) by invading fungus • (ii) osmoregulatory failure of invaded area Control measures In the initial stage, application of lime and sodium chloride treatment was found to be effective. CIFA produced a mixture of CIFAX, for controlling EUS but not much standardized. Treating the water with chlorine before letting in to the pond, avoidance of water use from large water body with improper water quality, use of filters in water channels to avoid wild fish entry and preventing the entry of predatory birds are central to disease management strategy.
