Comparative sensitivities of diagnostic procedures used to detect bacterial kidney disease in salmonid fishes

Kidney and spleen homogenates from each of 60 coho salmon (Oncorhynchus kisutch) and steelhead trout (Salmo gairdneri) were examined for detection of Renibacterium salmoninarum. The proportions of positives differed widely with the detection procedures used: in coho salmon, 5% were positive by the Gram-stain procedure, 10% by the direct fluorescent antibody test, 48% by bacteriological isolation, 65% by staphylococcal coagglutination, and 73% by counterimmunoelectrophoresis; in steelhead trout, 3% were positive by Gram-stain, 8.3% by fluorescent antibody, 17% by bacteriological isolation, and 67% by counterimmunoelectrophoresis. Renibacterium salmoninarum was not detected in either coho salmon or steelhead trout by immunodiffusion analysis.     

Isolation and characterization of Edwardsiella tarda from fall chinook salmon (Oncorhynchus tshawytscha).

A new bacterial pathogen of chinook salmon (oncorhynchus tshawytscha) was isolated from fish in Oregon's Rogue River. The bacteria are biochemically and serologically related to strains of Edwardsiella tarda. Initially isolated from chinook salmon, the bacteria were also pathogenic for steelhead and rainbow trout (Salmo gairdneri), and channel catfish (Ictalurus punctatus). The 50% lethal doses for chinook salmon, steelhead trout, and channel catfish injected intraperitoneally and maintained in 18 degrees C water were 4.1 x 10(6), 5.6 x 10(6), and 4.0 x 10(5) respectively. When chinook salmon and rainbow trout were injected intraperitoneally and held in 12 degrees C water, the mean lethal doses were 6.4 x 10(7) and 1.7 x 10(6), respectively. The invasiveness of the organism was low in steelhead trout exposed to the bacteria by the waterborne route. The optimum growth temperature of the bacteria in brain heart infusion broth was approximately 35 degrees C. The guanine plus cytosine content of DNA obtained from E. tarda isolated from salmon was 59 mol%.     

PKX, the causative agent of proliferative kidney disease (PKD) in Pacific salmonid fishes and its affinities with the Myxozoa

Proliferative kidney disease (PKD), caused by an unclassified protozoan (PKX), is reported from Pacific salmon, Oncorhynchus tshawytscha (Walbaum) and O. kisutch (Walbaum), and steelhead trout, Salmo gairdneri Richardson, held at the Mad River Hatchery in California, USA. The cumulative mortality attributed to the disease was 95, 13, and 18% respectively. The mortalities were greatest at mean water temperatures of 12-14 degrees C during July 1983. The ultrastructure of the PKX organism and its associated pathology during clinical disease in all three species were consistent with those of the parasite in rainbow trout (Salmo gairdneri) as described in European outbreaks. Significant mortalities did not occur after August, at which time the parasite could no longer be detected in the salmon species. The steelhead continued to exhibit parasites in the kidney interstitium and epithelium and lumens of the tubules. Myxosporidan trophozoites and developing spores were also observed in the lumens of the kidney tubules of these fish. Although a mixed infection with another parasite may have occurred, evidence suggests that the myxosporidans are later stages of PKX. They were only observed in fish exposed to water with the infective stage and were particularly prominent in recovering fish. The PKX organism is similar to UBO, an unclassified protozoan of carp suspected to be an early stage of Sphaerospora renicola Dykovà & Lom. Both parasites infect the blood and kidney, divide by endogeny, and are released by disintegration of the primary mother cell. The intraluminal myxosporean forms show similarities to Sphaerospora spp. in that they are monosporous and sporoblasts are formed within pseudoplasmodia.(ABSTRACT TRUNCATED AT 250 WORDS)     

The biology of the thorny-headed worms, parasites of trout acclimatized in the bodies of water of the Tien Shan]

A new species of Acanthocephala, a parasite of local Naemacheilus stoliczkai, was recorded from Salmo gairdneri after 9 years of its introduction into mountain water bodies of Tien Shan. Gammarus lacustris serves as an intermediate host. Dynamics of infection of trout for 9 years is shown.     

An electrophoretic analysis of plasma proteins from juvenile Oncorhynchus tshawytscha (Walbaum)

The plasma proteins of juvenile spring chinook salmon, Oncorhynchus tshawytscha , were examined as a function of development. Two-way gel electroprioresis of plasma proteins was conducted on samples taken from fish before initiation of downstream migration, from fish classified as actively migrating and from fish that were prevented from migrating. Analysis of the samples indicated that plasma proteins of fish changed depending on the migratory status of the fish. The results were consistent with the notion that some of the factors normally associated with smoltification in species such as steelhead trout, Salmo gairdneri , and coho salmon, O. kisutch , may well be temporally separated in Idaho O. ishawytscha.     

Rainbow trout (Salmo gairdneri) stocking and Contracaecum spp

A stocking program with rainbow trout (Salmo gairdneri) at High Rock Lake, Manitoba failed due to infections with large numbers of Contracaecum spp. larvae. Nematode larvae in the intestinal tract, body cavity and musculature made the fish unmarketable. A combination of experimental infections of rainbow trout and pelicans (Pelecanus erythrorhynchos), observations on the behavior of fish-eating birds, and numbers of larval Contracaecum spp. in minnow species led to the following conclusions. The introduction of rainbow trout attracted large numbers of fish-eating birds, particularly pelicans. Concurrent predation by rainbow trout on fathead minnows (Pimephales promelas), five-spined sticklebacks (Culaea inconstans), and nine-spined sticklebacks (Pungitius pungitius), concentrated the parasites. The combined increase in densities of the introduced fish host and fish-eating birds, and the short life cycle of the parasite, increased the numbers of parasites in rainbow trout over a season and in the indigenous minnow species between years. Numbers of larvae in the indigenous minnow species declined when stocking of rainbow trout was stopped and use of the lake by fish-eating birds, particularly pelicans, returned to normal levels.     

Glucuronidation and biliary excretion of phenolphthalein in temperature-acclimated steelhead trout (Salmo gairdneri)

Conjugative metabolism and biliary excretion of phenolphthalein (PP) were studied in steelhead trout (Salmo gairdneri) acclimated to 10, 14 or 18 degrees C. Significant seasonal effects were found on liver weight to body weight ratio and conjugative metabolism but not biliary excretion of free plus conjugate of PP. Temperature did not significantly interact with these relationships. PP was excreted in bile as parent compound and the glucuronide conjugate at all temperatures. Saturation of the excretory process was apparent at a dose of approximately 10 mumol/kg (i.p.) at 10 and 14, but not 18 degrees C.     

Selective haematological parameters in steelhead trout, Salmo gairdneri Richardson

Fifteen steelhead trout, Salmo gairdneri , were assayed for selective blood parameters. The trout were reared under flow-through conditions at the salmonid aquaculture facility at the University of Rhode Island. The means of the measured haematological parameters were: pH, 7·59 ± 0·05; pCO₂, 8·5 ± 1·05 mmHg; HCO₃-, 11·9 ± 1·9 meq/1; Ferri-Hb, 21·7 ± 2·0%; C1-, 147 ± 17·8 meq/1; Hct, 30·7 ± 4·8%.     

The influence of the zona radiata on the toxicities of zinc, lead, mercury, copper and silver ions to embryos of steelhead trout Salmo gairdneri

Eyed embryos of the steelhead trout (Salmo gairdneri) were significantly more resistant to zinc and lead but significantly less resistant to mercury, copper and silver if the zona radiata (egg capsule) was removed than if it was intact. The zona radiata appears to act as a cation exchanger and inhibits metals with high binding constants (Hg2+, Cu2+, Ag+) from entering the perivitelline fluid. Metals with low binding constants (Zn2+, Pb2+, Cd2+) rapidly penetrate the zona radiata and accumulate in the perivitelline fluid according to the Donnan equilibrium.     

Changes in haematocrit values in blood samples treated with and without oxygen: a comparative study with four salmonid species

Changes in haematocrit values under lowered oxygen tension and aerobically treated blood samples of rainbow trout Salmo gairdneri (Richardson), landlocked Baltic salmon S. salar (L.), brown trout S. trutta lacustris (L.) and lake trout Salvelinus namaycush (Walbaum) have been studied in vitro . The mean haematocrit value increased during 2 h incubation under lowered oxygen tension by 32.7 ± 3.1% in rainbow trout, 28.2 ± 2.8% in landlocked Baltic salmon, 29.2 ± 5.6% in brown trout and 25.2 ± 2.8% in lake trout. During corresponding incubation with oxygen the mean haematocrit value decreased below the starting level by 18.1 ± 1.9% in rainbow trout, 18.3 ± 4.8% in landlocked Baltic salmon, 22.4 ± 0.7% in brown trout and 11.8 ± 1.7% in lake trout. Consequently, the changes in the haematocrit values were greater in the species belonging to the genus Salmo than in that of the genus Salvelinus . The increase in the haematocrit values seems to have resulted from swelling of the erythrocytes and their decrease is similarly attributable to shrinking of the cells. The reasons for this swelling, which may be complicated, and its apparent significance for haematocrit determinations are discussed.     

Molecular filtration for recovery of waterborne viruses of fish

The effectiveness of tangential flow filtration (TFF) for the recovery of infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) from large volumes of water was evaluated. In laboratory studies, virus recovery from IHNV-seeded water following concentration by TFF was approximately 13%. However, the addition of 0.1 and 1% fetal bovine serum to deionized water stabilized the virus, increasing virus recoveries to 95%. The addition of 0.03 and 0.3% beef extract resulted in IHNV recoveries of 80 and 61%, respectively. Similar results were obtained with IPNV-seeded water. Field studies using the TFF procedure were conducted with water from areas where IHNV is endemic. IHNV was detected in effluent from an adult steelhead trout (Salmo gairdneri) holding pond at an estimated concentration of 1 PFU/5 ml of water. It was also detected at levels of 1 PFU/50 ml in water from a 2-m-diameter circular tank containing IHNV-infected steelhead trout fry. IHNV isolated in samples taken from the Metolius River was detected by TFF at estimated levels of 1 PFU/3 liters.     

Molecular filtration for recovery of waterborne viruses of fish.

The effectiveness of tangential flow filtration (TFF) for the recovery of infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) from large volumes of water was evaluated. In laboratory studies, virus recovery from IHNV-seeded water following concentration by TFF was approximately 13%. However, the addition of 0.1 and 1% fetal bovine serum to deionized water stabilized the virus, increasing virus recoveries to 95%. The addition of 0.03 and 0.3% beef extract resulted in IHNV recoveries of 80 and 61%, respectively. Similar results were obtained with IPNV-seeded water. Field studies using the TFF procedure were conducted with water from areas where IHNV is endemic. IHNV was detected in effluent from an adult steelhead trout (Salmo gairdneri) holding pond at an estimated concentration of 1 PFU/5 ml of water. It was also detected at levels of 1 PFU/50 ml in water from a 2-m-diameter circular tank containing IHNV-infected steelhead trout fry. IHNV isolated in samples taken from the Metolius River was detected by TFF at estimated levels of 1 PFU/3 liters.     

Migration tendency in juvenile steelhead trout, Salmo gairdneri Richardson, injected with thyroxine and thiourea

Juvenile steelhead trout, Salmo gairdneri injected with thyroxine (T₄) near the time of seaward migration exhibited a significantly lower migration tendency than untreated controls of fish injected with saline, thiourea, or a combination of T₄ and thiourea. Fish injected with thiourea alone or in combination with T₄ prior to the time of maximum migration tendency showed enhanced migration over untreated and saline injected controls and those injected with T₄ alone. Injections of T₄ or a combination of T₄ and thiourea elevated plasma T₄ and tri-iodothyronine (T₃) concentrations, while injection of thiourea alone depressed thyroid hormone levels relative to saline-injected controls. Plasma concentrations of T₃ and T₄ returned to control levels within 10 days in all groups. We suggest that thyroid hormones are antagonistic to mechanisms underlying seaward migration of steelhead trout and that these antagonistic effects must be overcome before migration tendency is expressed.     

Isolation of IPN virus from imported rainbow trout (Salmo gairdneri) in the P. R. China

Infectious pancreatic necrosis virus (IPNV) has been isolated first in the P. R. China from imported rainbow trout ( Salmo gairdneri ). The agent was neutralized with IPNV-Sp-antiserum and proved to be pathogenic to fry of rainbow trout; mortality rates were 95% at a water temperature of 10°C.

Zusammenfassung

Die Isolierung des IPN-Virus von importierten Regenbogenforellen (Salmo gairdneri) in der Volksrepublik China
Das Virus der infektiösen Pankreasnekrose wurde erstmals in der Volksrepublik China von importierten Regenbogenforellen ( Salmo gairdneri ) isoliert. Der Erreger erwies sicn als pathogen für Regenbo-genforellenbrut; die Mortalität betrug 95 % bei einer Wassertemperatur von 10°C.

Résumé

L'isolation du virus IPN de truites arc-en-ciel (Salmo gairdneri) importées dans la République populaire de Chine
Le virus de la nécrose infectieuse du pancréas a été pour la première fois isolé de truites arc-en-ciel importées en République populaire de Chine. l'agent a été neutralisé avec l'antisérum IPNV-Sp et s'est révéléêtre pathogène pour le fret de la truite arc-en-ciel. La mortalitéétait de 95%à une température de 10°C.     

Effects of low pH on the chorion of rainbow trout, Oncorhynchus mykiss, and brown trout, Salmo trutta f. fario

Morphological studies on the effect of low pH on egg shells (chorion) of rainbow trout, Oncorhynrhus mykiss Walbaum (formerly Salmo gairdneri ), and brown trout, Salmo trutta f. fario L., showed that the plugs of the outer layer of the chorion, which block the channels of the underlying layer, developed distinctive vacuolization at low pH exposure. This may lead to loss of chorional semi-permeability. Chorions were incompletely degraded at low pH inducing hatching problems. Partially hatched alevins showed only a small local zone of dissolution of the chorion around the head of the embryo preventing the larvae from being freed.     

Diel feeding periodicity, daily ration and prey selectivity in juvenile brown trout in a subarctic river

Feeding of age-1 brown trout Salmo trutta in a third-order river in northern Finland was usually highest in the twilight hours and lowest around midday. Diel periodicity in food intake was less distinct and rarely significant for age-0 trout. Daily rations declined seasonally, being lowest in October, and highest in June (age-1 trout) or early August (age-0 trout). Prey selection did not differ between day and night, but differences between age classes and sampling dates were distinct. Age-0 trout preferred Ephemerella nymphs in summer and Micrasema larvae later in the season. Age-1 trout fed selectively on caddis larvae on all sample dates. Aerial insects and Baetis nymphs were avoided by both age classes on most occasions. These patterns of preference are probably explained by a trend towards epibenthic feeding, which may be a predominant foraging mode in some trout populations. Nevertheless, repuscular peaks in feeding periodicity suggest that trout were able to capitalize on the increased availability of drifting prey in the twilight, especially in the early summer months.     

Use of lesion filtrates for the transmission of UDN (ulcerative dermal necrosis) in salmonids

Spawning Atlantic salmon, Salmo salar (L.), brown trout, Salmo trutta (L.) and rainbow trout, Salmo gairdneri (Richardson) were held in tanks for four weeks and then injected with filtrates from lesions of salmon naturally infected with UDN. In some cases prednisolone acetate was included in the inoculum. Water temperatures were recorded daily and the time of appearance of the lesions was noted. Passage experiments using extracts of these lesions were carried out.     

Seasonal population dynamics of the nematode Cystidicoloides tenuissima (Zeder) from the River Swincombe, England

The seasonal population dynamics of adult and larval Cystidicoloides tenuissima were studied in its definitive hosts brown trout, Salmo trutta and juvenile Atlantic salmon, S. salar , and mayfly intermediate host, Leptophlebia marginata , from the River Swincombe, Dartmoor National Park, Devon, U.K. Infective larvae were present in each mayfly generation for almost its entire duration in the steam benthos. The infection parameters (prevalence and mean intensity) and maturation in the fish indicated C. tenuissima was an annual parasite exhibiting a seasonal periodicity and also systematic variation with the host age. Maturation was correlated to river water temperature. Infection parameters increased from September to May, then declined in June and July and remained relatively constant for the rest of the summer. Variation in the fish infection parameters over time, site, and host species appeared to be controlled by transmission related events; the availability of infective larvae, host feeding behaviour and water temperature. The availability of infective larvae and host diet controlled the rate at which parasites were added to the parasite population, but the pattern of gains and losses was determined by a temperature dependent rejection response.     

Tolerance to gas supersaturation in fresh water and sea water by steelhead trout, Salmo gairdneri Richardson

The euryhaline status of steelhead trout, Salmo gairdneri , smolts was challenged in sea water for 2 weeks after which half of the total fish population was returned to fresh water. Acclimation continued and created two test populations in 29%osea water and fresh water. Subsequently these fish were exposed in fresh water or sea water to approximately equal hyperbaric dissolved total gas pressures (ΔP) of 190 mm Hg or about 125% of barometric pressure. Sea water was easier to supersaturate with air and required only about 10% of the entrained air which was required in fresh water at the same temperature and pressure. Mean time to first mortality was sooner in sea water. Mean times to mortality (10–50%) were not significantly different between fresh water and sea water, but there was a noticeable trend for longer survival in fresh water.     

Pituitary Activation by Bacterial Endotoxins in the Rainbow Trout (Salmo gairdneri)

Endotoxins from Escherichia coli and Aeromonas salmonicida caused marked cortisol production in the rainbow trout (Salmo gairdneri).