Cold water sickness
The cold-water disease (engl. Coldwater disease , abbreviated as CWD) is a in all species of salmon fish world-occurring disease, associated with septicemia , extensive lesions of the skin, necrosis or ulcer .
In commercially operated fish farms or pond farms, in particular those of the rainbow trout ( Oncorhynchus mykiss ) and the silver salmon ( Oncorhynchus kisutch) , cold water disease is one of the most frequent and lossy diseases. Cold water sickness is caused by a bacterial mixed infection of the two types of bacteria Flavobacterium psychrophilum and Flavobacterium branchiophilum . Flavobacterium psychrophilum is the main culprit in trout .
Epidemiology
The disease was first detected in rainbow trout saplings in the United States in 1947. Since then, cold water disease has been a widespread problem within aquaculture representatives of salmonids. It has been observed increasingly in Europe since the 1980s ( Bernadet & Kerouault , 1989). The disease only breaks out within a temperature range between 4 and 12 ° C. The septicemic form is only found in young fish and mortality rates of well over 50% are not uncommon. The disease is transmitted both horizontally and vertically . Female fish transmit the disease predominantly vertically, males predominantly horizontally. Further transmissions are possible and proven via the egg.
Clinical picture
Cold water disease is typical of necrosis of the skin and muscles on the tail and paired fins of the affected fish. After a proliferation phase of the epidermis , extensive and massive necrosis occurs, which can lead to the complete loss of the fins. In the edge area of this necrotic altered skin surface, pronounced, heavily bleeding halos can be found, which in the final stage lead to massive tissue loss.
Long-term effects are, in surviving fish in the acute phase of the disease, skeletal deformations and central nervous symptoms with inflammatory changes in the cranial skeleton . Bacteria are found in almost all internal organs during the course of the disease. The spleen is severely affected by the explosion of the bacteria and enlarges. The result is a perforation with subsequent decomposition of the abdominal wall and exposure of the organ.
The septicemic form occurs only in juvenile fish and manifests itself as anemia and bulging eyes ( exophthalmos ), while in adult animals mainly pathological changes in the tail peduncle and paired fins are observed.
Parts of the body where the disease occurs:
- Dorsal fin ( columnar disease , saddleback disease)
- Pectoral fin (fin rot)
- Caudal fin (tail rot, peduncle disease)
- Gills (gill rot)
causes
Cold water sickness is triggered by immune depressive factors that are triggered by stress, such as poor environmental conditions, poor management and high bacterial pressure due to overcrowding.
proof
The bacteria can be detected by growing them from modified parts on cytophaga agar . After 72 hours, yellow-pigmented, flat colonies form below an incubation temperature of 20 ° C. Characterization is carried out with alloantisera.
swell
- Rudolf W. Hoffmann: Fish diseases, Eugen Ulmer Verlag, Stuttgart 2005, ISBN 3-8001-2739-3 .
- E. Amlacher: Pocket book of fish diseases. 5th edition, Gustav Fischer Verlag, Jena 1990, ISBN 3-055-00190-7
- E. Amlacher: Pocket book of fish diseases. Basics of fish pathology, 6th revised edition, Gustav Fischer Verlag, Stuttgart, Jena 1992, 149–177 ISBN 3-3340-0350-7
- Toranzo, AE & Barja, JL (1993): Fry mortality syndrome (FMS) in Spain. Isolation of the causative bacterium Flexibacter psychrophilus. Bull Eur Ass Fish Pathol 13, pp. 30-31.
- DJ Speare, RJF Markham, B. Despres, K. Whitman, N. MacNair: Examination of Gills from Salmonids with Bacterial Gill Disease using Monoclonal Antibody Probes for Flavobacterium Branchiophilum and Cytophaga Columnaris, J VET Diagn Invest, October 1995; vol. 7, 4: pp. 500-505. Department of Pathology & Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island CIA 4P3, Canada