This is a report concerning the diseases in artifical salmon propagation programme in Hokkaido. Although the diseases during the artificial propagation of salmons are usually not so frequent as those in fish culture, the preventive and restraint of them are indispensable to the salmon propagation on account of their artificial mass production. It has been widely known that almost all the diseases of salmon resulted in the mass mortalities are caused by well described microorganisms. Furunclosis caused by Aeromonas salmonicida occurs often in the immature adult fish kept in a holding pond untile they reach maturity. Bacterial kidney disease has now been recongnized in cultured salmon. Infections with Saprolegnia sp. and Achlya sp. have been usually found in adult fish of salmons holding pond. Although most of the saprolegnoid infections are generally considered to be secondary condition, kokanee salmon, Oncorhynchus nerka var. adonis, has been heavily infected with Saprolegnia shikotsuensis sp. nov. from 1974 to 1978, except 1976. Gill diseases caused by various bacterial species or protozoa are found frequently in salmon fry. Especially, in chum salmon fry bacterial gill idseases tend to increase recently along with the diffusion of fry feeding. Among the virus diseases that occur in salmonid in epizootic proportions, so far only IHN is found in masu salmon and kokanee salmon at times, but it is still not recorded in chum salmon fry in Hokkaido. External protozoan disease caused by Tricodina sp. is usually not so frequent and serious as the bacterial and virus diseases.
Attempts have been done by the present author to improve the method for rearing and liberating chum salmon(Oncorhynchus keta)fry in Iwate Prefecture since 1967. As a result the return rate could be increased by liberating fry after being cultured in seawater for some time. Vibriosis was noted to be the major problem in the culture of fry in seawater. It often occurred when water temperature rose rapidly to 11°C and above. A coho salmon(O. kisutch)culture using net pens set in the bay has been practiced commercially in recent years in the Northern Japan.Vibriosis is a serious problem in the culture of coho salmon fry, too. The matter that fish culturists most ardently hope is rapid development of effective vaccines and practical vaccine delivery systems against vibriosis.
Two hundred nineteen strains of causative organisms of fish vibriosis, which were isolated from various kinds of diseased fish cultured from all over the country, and 29 reference strains were examined by means of ordinary taxonomy, numerical taxonomy, DNA base composition and serological analysis. One hundred and seventy strains(phenon I, see Fig.1)isolated from coho salmon(Oncorhynchus kisutch), ayu(Pleocoglossus altivelis), eel(Anguilla spp.), yellowtail(Seriola quinqueradiata)and amberjack(Seriola purpurascens)were identified as V. anguillarum. Twenty five strains(phenon II, see Fig.1)were not identified as V. anguillarum, but were closely related to above taxon in many characteristics.These strains were isolated from rainbow trout(Salmo gairdnerii), yamabe(O.masou var.ishikawae)and amago(O. rhodurus var. macrostomus)reared in fresh water. Twenty one strains isolated from ayu, yellowtail, red sea bream(Chrysophrys major)and anchovy(Engraulis japonica)could not be identified as any species in genus Vibrio, and many differences were observed among them. The other 3 strains isolated from rainbow trout and ayu were identified as Aeromonas spp. One hundred and ninety two strains out of 195 strains identified as V.anguillarum and its related organisms(phenon I and II), were distinguished into three serological groups according to the serological analysis of the somatic antigens.Serotype J-O-1 was comprised of 100 strains of V. anguillarum and 25 strains related to the species. One hundred and ten strains out of the above 125 strains were originally isolated from ayu, eel, rainbow trout, amago and yamabe reared in fresh water.Serotype J-O-2 was comprised of 11 strains isolated from ayu and eel reared in fresh or salt water.Serotype J-O-3 was comprised of 56 strains isolated from ayu, coho salmon, yellowtail and amberjack.Except the 10 strains from ayu in fresh water, 46 strains were isolated from the fish reared in sea water.
Licensed Vibrio anguillarum bacterin was developed in 1977. The purpose of this paper is to review data used for implementing an efficient vaccination program. The bacterin is applied by two delivery systems : 20 second immersion and shower application. These will be illustrated. The bacterin is a bivalent combination of Vibrio anguillarum, Type I (Japanese Type C) and II (Japanese Type A), which have been shown to have no interference with each other while being antigenically distinct. Protection from challenge with virulent V. anguillarum following immunization has developed within 10 days at holding water temperatures of 18°C and 10°C while over 30 days holding was required for fish vaccinated and held in a water temperature of 4.8°C. Successful vaccination with licensed Vibrio bacterin has been demonstrated in coho (Oncorhynchus kisutch), chinook (O. tshawytscha), sockey (O. nerka), chum (O. keta), and pink salmon (O. gorbuscha); rainbow trout (Salmo gairdneri) and Atlantic salmon (S. salar), goldfish (Carassius auratus), and angelfish (Pterophyllum scalare). Most salmonids first become capable of responding to vaccination as measured by resistance to laboratory challenge, at an average size of 1.0 g. The duration of the immune response for several salmonid species tested was short for fish vaccinated at a 1.0 g average size. Tests have demonstrated that duration of over 400 days can be obtained if fish are larger than 4 g size at time of vaccination. The variations in onset and duration of protection of four species of salmonids will be discussed. Serological and protection studies have been done with Vibrio anguillarum isolates obtained from around the world. Licensed Vibrio bacterin has successfully protected fish from challenge with Type I (C) and II (A) V. anguillarum isolates from Japan, U.S.A., Norway, and Italy. Tests with chum and chinook salmon have demonstrated that they can be vaccinated with licensed bacterin and then placed into salt water a very short time afterward and still develop protection from natural challenge. Also successful vaccinations can be done with fish held in salt water by the 20 second immersion method using salt water as the bacterin diluent.
Ceratomyxa shasta is a myxosporidan parasite of salmonids. The distribution of sites in which fish become infected with C. shasta appears to be restricted to several river systems of the Pacific Northwest coast of the United States. The objective of this study was to investigate the biology of C. shasta in hopes that this information would lead to measures of controlling ceratomyxosis. As the result of this study, the range of occurance of C. shasta was extended to include the lower Willamette River, Oregon. Susceptible salmonids were held in liveboxes within the river system to determine the extent of the river where they would become exposed to ceratomyxosis. No infections were obtained in the exposed fish at or upstream from mile 134. The source of ceratomyxosis for the Willamette appears to be the main river channel and the disease agent does not enter from tributaries. For most years tested, salmonids developed ceratomyxosis when exposed to Willamatte River water from early April through mid-November . Attempts to transmit the disease using infected tissues, a mud substrate, and flowing Pathogen free water were unsuccessful. Laboratory transmission of C. shasta was accomplished by injection of the trophozoite stage of the parasite. The susceptibility of selected salmonid species to ceratomyxosis by injection was also determined. Nine salmonid species were tested for their susceptibility to ceratomyxosis by natural exposure. A high percent mortality and a short mean time to death characterized salmonids with high susceptibility to the disease. These inclued rainbow, cutthroat and brook trout and chum and one strain of fall chinook salmon. Sockeye and spring chinook salmon had low susceptibility to ceratomyxosis as indicated by low percent mortality and an extended mean time to death. Brown trout, Atlantic and coho salmon were moderately susceptible and had intermediate values for percent mortality and mean time to death. Variation in susceptibility to ceratomyxosis was investigated between four strains of fall chinook salmon. Three strains originated from hatcheries located within the lower Columbia River system, which has been shown to contain C. shasta, while the fourth was from an Oregon coastal river, where the disease does not occur. Fish of these four strains were exposed to ceratomyxosis which was subsequently detected in 95 percent of the coastal fall chinook salmon strain and only 9 percent of the Columbia River basin strains. Fish of the strains originating from the Columbia River basin possessed a high degree of resistance to the disease. That resistance can be passed genetically, is possible, since none of the individuals tested had been previously exposed to the disease. Two strains of rainbow trout which were cultured for resistance to cetatomyxosis were exposed to the disease. Both strains displayed resistance to ceratomyxosis and illustrated that resistant strains could offer a solution to fisheries agencies which manage waters where ceratomyxosis occurs. The histopathology of rainbow trout infected with C. shasta was described. A group of rainbow trout were exposed to ceratomyxosis and tissue samples were examined histologically to check the progress of the disease with time. Infection was first detected in the pyloric caeca and descending intestine followed by a massive infection of the digestive tract and its associated organs. Cells of the lamina propria, stratum compactum, and stratum granulosum proliferated to form a fibrous granulomatous layer in places where the intestinal mucosal epithelium was sloughed off. Infection of visceral organs other than the intestines occurred from trophozoites which penetrated into the surface of the organs from the body cavity. Death of the host occurred when trophozoites infected the digestive system for most of its length.
A filamentous bacterium isolated from salmonid fish with bacterial gill disease was reviewed.The disease fish were collected in Gunma, Japan and Oregon, U.S.A. All cultures were found to be uniform in their morphological and physiological characteristics. They showed neither gliding motility nor swarming growth on agar media, such as cytophaga agar. On the basis of the characteristics given in the 8th edition of Bergey's Manusl, the bacteria fit most closely into genus Flavobacterium, section I. The presence of a common antigen showed a similarity between the Japanese and the Oregonstrains. However they were separated into two serological groups on the basis of agglutininadsorption tests. All cultures appeared abundantly on the surface of the gills of juvenile rainbow trout within18-24hours after exposure to the bacterial su.spension in an aquarium. However mortality among exposed groups of fish varied widely in different experiments.
Virus isolation and neutralization test are too time consuming for diagnosis on fish viral diseases. Minimum mortality and prevention from following transmission are brought by proper and timely countermeasures. Therefore more rapid diagnosis of the viral diseases is desired strongly. Several procedures developed in medicine for more rapid diagnosis are introduced here and some of them applied to the fish viral diseases are reviewed. Most rapid diagnosis was performed using direct fluorescent antibody technique of stamp smear preparation of IPN infected trout tissues. Enzyme antibody technique is hopeful having many advantages against fluorescent antibody technique. Further studies will be necessary to applicate some hopeful and available methods to the fish viral diseases.
The papers on a taxonomical study of Saprolegnia fungus was very few in Japan. Therefore the studies on classification of it isolated from the lesions of salmonid fish with fungus disease have been done by author. As literature which deals with the taxonomy of Saprolegnia species isolated from fishes including salmonids is scanty in Japan, it was decided to investigate this problem. During the course of the investigation for the past six years three species of fish pathogenic fungi, S. australis, S. shikotsuensis and S. diclina, were identified. S. australis was isolated from the base of the dorsal fin of rainbow trout fingerlings of about 1.2 g in body weight with saprolegniasis at the Koide branch of the Niigata Prefectural Freshwater Fisheries Experimental Station in 1976. S. shikotsuensis sp. nov. was isolated from the caudal fin of wild kokanee salmon, Oncorhynchus nerka var. adonis, with fungus disease in Lake Shikotsu of Hokkaido Island in 1974 and 1975. S. diclina was isolated from the abdominal cavity of hatchery-reared fry of amago salmon, Oncorhynchus rhodurus with visceral mycosis at farms in Gifu Prefecture in 1975. Recently, NEISH (1976) mentioned that S. parasitica might be regarded as a synonym of S. diclina. His new conception of S. diclina was reviewed and some other problems on the taxonomical study of the genus Saprolegnia (fungus) were discussed in this paper.
In this review, an autline of the parasites caused as fish diseases and problems of food hygiene occurred in salmonid fishes in Hokkaido have been described, including Nosema takedai, Haplosporid, Tetraonchus awakurai, Acanthocephalus minor, Lepeophtheirus salmonis, Rocinera maculata, glochidia of Margaritifera laevis, Diphyllobothrium latum and Anisakis sp. larva.