Edwardsiella tarda (Paracolobactrum anguillimortiferum) and Pseudomonas anguilliseptica are important pathogens of pond-cultured eels in Japan. Recent investigations on their taxonomy, modes of pathogenesis, and sources are reviewed. Pesudomonas chlororaphis was recently isolated from diseased fry of Amago trout, and this bacterium was proved to be pathogenic to fish. “Branchionephritis” is a malignant coldwater disease of pond-cultured eels. Its causative agent is still unknown, though flexibacteria are occasionally isolated from the gills of diseased eels.
The organization and operation of the fish health program in the Pacific Region (British Columbia and the Yukon Territory) of Canada are described and placed within the context of the Federal Fisheries Act that basically governs all fisheries activities in Canada. This program has three components: health certification, diagnostics-consultation, and research, each of which is briefly described. Frequently occurring or threatening diseases or disease agents in the Pacific Region are listed and some comments are made on the more important ones.
Although some diseases are not affected by subtle environmental changes, others are. Factors which may influence infection or the course of disease are: temperature, gaseous supersaturation, oxygen deficiency, mechanical and physiological trauma of the fish, malappropriate water chemistry, pollution, eutrophication, media for spore retention, and presence of intermediate hosts. Aviatminoses and neoplasias are often related to environmental changes.
This overview concerns fish virology in North America in 1971-75, with emphasis on the virulent viruses: infectious pancreatic necrosis virus, infectious hematopoietic necrosis virus, channel catfish virus, and a newly isolated herpesvirus that is lethal for young rainbow trout (Salmo gairdneri). Methods of detection and identification, new research findings, and specific problems that require research are reviewed briefly for the well-known viruses. Biophysical characteristics of a newly found herpesvirus and its known effects on young trout and Atlantic salmon (Salmo salar) after experimental infection are described. Recent research of the Eastern Fish Disease Laboratory is described with particular reference to bacterial diseases and Myxosoma cerebralis (whirling disease of trout). The recently established section of Biological Standards of the Laboratory is an international center for the preparation, standardization, and distribution of biological reagents needed for identification and detection of infectious agents of fishes. Available reagents are listed. Similarly, the purpose, distribution, and plans for growth of Fish Health News, the quarterly bulletin, are described.
Experimental work done with the immunization against several fish pathogens is described. The agents studied included Flexibacter columnaris, Aeromonas salmonicida, Vibrio anguillarum and Infectious Hematopoietic Necrosis Virus (IHNV). At the present, it appears that vaccines prepared against IHNV and bacterins against V. anguillarum show potential for use in aquaculture.
Twenty different fish diets marketed in Japan were examined for the microbial flora.The total counts of aerobic bacteria determined at 30°C ranged from 1.8×103 to 8.0×105 pergram of diet with a mean value of 1.4×105. The microflora of these diets were consisted mainly of Gram-positive bacteria, and the most predominant organisms belong to the genus Bacillus and Staphylococcus. The total fungal plate counts determined at 20°C ranged from 4.0×10 to 9.6×104/g. of the diet with a mean value of 1.1×104/g. Coliform organisms were detected in 16 samples and Escherichia coli was isolated from 10 out of the 16 samples. Streptococcus were found in 4 samples. No Salmonella was detected but Vibrio was detected in 3 out of the samples. Clostridium perfringens producing lecithinase was isolated from 10 out of the 20 samples.
Abstract: A total of 33 cases of cataract found in cultured fishes were studied by the histologic method. The pathology of lens of a cataract in fingerling salmonids was characterized by regressive processes, abnormal proliferation and floating lens nucleus. This type of cataract may be classified as morganian cataract. The pathological changes in the lens tissues of worm cataract in young rainbow trout and of whitish conditions of the eye in yellowtails were briefly described.
Three proved and two suspected viral diseases of cultured fishes in Japan were introduced in this paper. They are of salmonids and eel. As for IPN and IHN, research works were reviewed. From an epizootic of European and Japanese eel producing severe mortality, a virus was isolated in RTG-2 cells, being the closest to Fr 21 among five serotypes of IPN virus. Virus particles were found in cytoplasm of the kidney cells of eel of natural epizootic and in RTG-2 cells infected with the isolant. They are pentagonal or hexagonal having a diameter 68 to 77 mμ. This virus fulfilled the River's postulates. On an epizootic of landlocked nerka fry, virological diagnosis was tried using RTG-2 cells and proved a syncytium-forming agent. Viral particles, being similar shape to Herpesvirus were found in the process of budding on the surface of RTG-2 cell having a diameter 220 to 250 mμ. From an epizootic of American eel, a virus was isolated in RTG-2 cells, not being neutralized with either rabbit antisera of IHN and VHS. This virus particles are bullet shape having 140 to 150mμlong. Histopathological findings on these natural epizootic indicate generally regressive pathological change. Severely affected eels EVE show nephrosis, glomerulonephritis and splenic change. With NeVTA disease, affected nerka fry show granular degeneration in skeletal musculature, syncytium-formation and cytoplasmic inclusion in interstitial cells on the kidney. In EVA-affected American eel, hemorrhage and degeneration in skeletal musculature, hyperemia in branchial vessels as well as hemorrhage into Bowman's space are found as principal change.
Parenteral and oral vaccination were made against furunculosis of native trouts. In the case of parenteral vaccines, 0.1 mg of formalin killed cells suspended in saline were injected intraperitoneally. The survival rate at the end of experiment was higher in the vaccinated group than in the control group. Agglutination titer was reached higher than 1, 000 and had maintained for long time in adjuvant vaccine group. Another experiment was done with fingerings of native trouts fed to 0.15 or 0.3 mg of vaccine per fish a day. Efficacy of oral vaccine was compared with both mortality and challenge test of intramuscular injection or bacterial bathing. The mortality due to furunculosis was higher in the control group than in the vaccinated group.
The ability of circulating leucocytes of non-immunized, cultured sockeye salmon to phagocytize bacteria in the blood stream was examined using two techniques; cannulation of the dorsal aorta (for the injection of bacteria and for blood sampling) and intracardiac injection. With the first technique no phagocytosis was observed in the peripheral blood but there was a rapid uptake of bacteria that was particularly impressive in the kidney. Some phagocytosis in the blood stream, mostly by polymorphonuclear leucocytes, was demonstrated using the second technique but there was the possibility that these phagocytes had actually drained from the renal portal system following caudal blood sampling. The results so far confirm the observations of others that phagocytosis in the peripheral blood of salmonids is insignificant or non-existent.
A study on the actual condition and changes of normal bacterial flora in the intestines of salmonids was carried out to determine the actual status of bacterial flora in the digestive tract, particularly in the intestines, in the course of their life cycle, i. e. migration from fresh water to the sea and back to the original river. From the results of this study, it would be concluded as follows. The intestinal microflora of healthy salmonids are mainly composed of the genus Aeromonas and the family Enterobacteriaceae of a so called terrestrial type, if they are living in fresh water. Contrarily, the flora are mainly composed of the genus Vibrio of marine or halophilic type when they are living in sea water. If fish move to the sea or upstream a river in their life cycle, the flora in their intestines would undergo changes in order to adequaely adapt the fish themselves for their living environments.