[Pathogenic bacteria of fish diseases. 1. Fish pathogenic bacteria and fish diseaseS].
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A total of 47 fish located in 10 lake and river systems in northern Finland were examined for furunculosis, enteric redmouth diseases (ERM), viral fish diseases and the parasite Gyrodactylus salaris. Furunculosis was found in 2 fish farms in different watercourses, ERM in 8 fish farms in 3 watercourses and viral diseases were not found at all. G. salaris was looked for only in salmon and rainbow trout and was found in both species in 3 farms belonging to 2 watercourses.
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The Diseases of Fish Act 1937 of Great Britain is almost certainly the longest-standing example of national legislation specifically devised to control fish diseases. It was introduced in response to several outbreaks of furunculosis disease in wild salmon and other fish species in the rivers of England, Wales and Scotland, which were attributed to the importation of infected live rainbow trout from Germany. The Act totally prohibited the importation of live salmonids into Great Britain, and made it illegal to import salmonid ova and all live freshwater fish species without a licence. The Act also provided powers for authorised persons to enter onto any land to confiscate any fish, ova, foodstuff or articles suspected to have been illegally imported into Great Britain. Moreover, the Act enabled any disease to be designated as 'notifiable', meaning that even the suspicion of its presence in any waters must be reported to the official services. This legislation was eventually amended and extended by the Diseases of Fish Act 1983 to make it a legal requirement for all fish-farming businesses to become registered with the official services, and to maintain records of the movement of fish and fish ova into and from their sites. In 1986, additional powers were introduced under the Animal Health Act 1981 to limit the importation of dead, ungutted salmonid fish. In 1993, the legislation was amended to remove any legal conflict with European Economic Community Council Directive 91/67/EEC. In addition, the Diseases of Fish (Control) Regulations have since been passed so that new European Union rules for the control of infectious salmon anaemia, viral haemorrhagic septicaemia and infectious haematopoietic necrosis may be enforced nationally.
The treatment of fish diseases is relatively unsophisticated. Administration of drugs may be by solution in water, incorporation in feed or by injection. Many of the drugs used are traditional remedies although antibiotics and anaesthetics are being increasingly employed. The efficacy of the drugs may be affected by various environmental factors such as pH, the presence of organic matter and temperature. Some of the drugs may themselves affect the environment by destroying plants or bacterial filters.
The frequency of fish diseases diagnosed at the Fish Disease Laboratory at the University of Berne from 1979 to 1988 is presented. Parasitic infections have been found to be the most frequent diagnosis. Among noninfectious diseases poisonings were predominant. Six infectious diseases have been considered to be economically relevant. These diseases (according to their frequency: Gyrodactylosis, Costiosis, Ichthyophthiriosis, Viral Hemorrhagic Septicemia (VHS), Saprolegniosis and Furunculosis) were further analysed. Their incidence varies with season, species, origin and length of fish. Possible explanations for these findings are discussed.
Fish suffer from environmental, nutritional, viral, bacterial, parasitic, and neoplastic diseases, many of which are similar to those of higher animals. The prevention and treatment of these diseases follow the same principles as diseases of other animals. Fish culture is similar to poultry husbandry in that large numbers of animals are crowded into relatively small areas, feeding is free choice, and medication for systemic infections is usually oral. External treatment of fishes is more common than of poultry, due to a higher frequency of external diseases. Many of the drugs and chemicals used in chemotherapy of fishes are the same as for higher animals. The following is a brief review of the more important drugs and their methods of administration.
Aeromonas hydrophila, a normal inhabitant of aquatic environments, is an opportunistic pathogen of a variety of aquatic and terrestrial animals, including humans. A. hydrophila PPD134/91 is defined as virulent whereas PPD35/85 is defined as avirulent on the basis of their different LD50 values in fish. Suppression subtractive hybridization (SSH) was used to identify genetic differences between these two strains. Sixty-nine genomic regions of differences were absent in PPD35/85, and the DNA sequences of these regions were determined. Sixteen ORFs encoded by 23 fragments showed high homology to known proteins of other bacteria. ORFs encoded by the remaining 46 fragments were identified as new proteins of A. hydrophila, showing no significant homology to any known proteins. Among these PPD134/91-specific genes, 22 DNA fragments (21 ORFs) were present in most of the eight virulent strains studied but mostly absent in the seven avirulent strains, suggesting that they are universal virulence genes in A. hydrophila. The PPD134/91-specific genes included five known virulence factors of A. hydrophila: haemolysin (hlyA), protease (oligopeptidase A), outer-membrane protein (Omp), multidrug-resistance protein and histone-like protein (HU-2). Another 47 DNA fragments (44 ORFs) were mainly present in PPD134/91, indicating the heterogeneity among motile aeromonads. Some of these fragments encoded virulence determinants. These included genes for the synthesis of O-antigen and type II restriction/modification system. The results indicated that SSH is successful in identifying genetic differences and virulence genes among different strains of A. hydrophila.
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Ten different strains of Aeromonas salmonicida that were isolated from diseased fish were grown under identical conditions (24 h at 25 degree C) in 3% (wt/vol) tryptone soya broth medium supplemented with vitamins and inorganic ions. In each case the extracellular proteins that were formed were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and it was found that there were two significant common components, one with a molecular weight of 70,000 and the other with a weight of 56,000. Application of enzyme purification techniques to the supernatant fraction proteins of a culture of one of the strains resulted in the isolation of a 70-kilodalton (kDa) component, which was found to be a serine protease, and a 56-kDa component, which was hemolytic to trout erythrocytes. Rocket immunoelectrophoresis with rabbit antibodies to the isolated protease and hemolysin showed the same antigenic components in the supernatant fractions of all the cultures. These activities were assayed, and protease activity was found to vary by a factor of three, from 59 to 195 U/ml, while the range of hemolytic activity was over a narrow band, from 28 to 43 U/ml. There was an inconsistency between the immunoelectrophoretic and direct assay data in only one case. This indicated the presence of additional hemolytic activity, in addition to the 56-kDa component. The detection of large amounts of the same protease and hemolysin, two potent degradative activities, in a random series of strains of A. salmonicida suggests that they may be obligatory virulence factors in the development of furunculosis.
The entire diagnostic material of the Fish Disease Laboratory at the University of Berne from 1979 to 1988, a total of more than 3800 cases, is presented. Not included is material of import controls and material from experimental work. The following criteria were evaluated: fish species, origin and length of fish, season, infectious and noninfectious diseases. Furthermore, the results were investigated for changes of the composition of fish species and number of diseases within the ten-year period and for a seasonal influence on the outbreak of diseases. More than 40% of all fish investigated were rainbow trout, followed by brown trout, omamental fish and cyprinids. Over 40% of fish originated from private fishfarms whereas 20% were of governmental origin (governmental fishfarms, rivers, lakes) and 20% from aquaria. Parasites were present in more than 40% of all cases. Bacterial infections were diagnosed in nearly 30%, viral infections in 6% and fungal diseases in 5% of all cases. 20% of all cases concerning noninfectious diseases were caused by unfavourable environmental conditions whereas the incidence of diseases related to nutrition was less than 10%. The occurrence of the different diseases was waxing and waning over the period of ten years but no definite tendencies could be emphasized. However, most of the diseases investigated demonstrated a significant seasonal influence.
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Taxonomy of the motile species of the genus Aeromonas is briefly discussed. It is suggested that Aeromonas organisms, isolated from outbreaks of red mouth of trout, red sore of pike, infectious abdominal dropsy and hemorrhagic septicemia of warm water fish, and which show acid and gas in glucose broth, production of 2,3-butanediol hydrogen sulfide from motility sulfide medium, presence of cytochrome oxidase, and hydrolysis of starch, be designated as Aeromonas liquefaciens. These tests also serve to differentiate A. liquefaciens from fish-pathogenic Pseudomonas fluorescens and from enteric bacteria.
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