V. E. Ostland

Flexibacter Maritimus Associated with a Bacterial Stomatitis in Atlantic Salmon Smolts Reared in Net-Pens in British Columbia

Abstract Filamentous yellow-pigmented bacteria (YPB) were consistently isolated from outbreaks of bacterial stomatitis (“mouth rot”) affecting smolts of Atlantic salmon Salmo salar after seawater entry in British Columbia. Six representative YPB isolates were selected, and phenotypic characterization demonstrated that they shared morphological, physiological, and biochemical similarities with the Flexibacter maritimus reference strains ATCC 43397 and ATCC 43398T (type strain). Polyclonal antisera raised against one British Columbia mouth rot isolate (MRJ) and strains ATCC 43397 and ATCC 43398T were used to examine the antigenic relationships between the YPB from British Columbia and these reference strains. Using agglutination, immunodiffusion, and western immunoblots, it was demonstrated that the British Columbian YPB were antigenically related to ATCC 43397 and ATCC 43398T. Furthermore, immunohistochemistry indicated that the filamentous YPB recovered from outbreaks of mouth rot were antigenically relat...

Use of Hydrogen Peroxide to Treat Experimentally Induced Bacterial Gill Disease in Rainbow Trout

Abstract Bacterial gill disease, experimentally produced in rainbow trout Oncorhynchus mykiss exposed to Flavobacterium branchiophilum, was effectively treated by using 1-h static baths containing hydrogen peroxide as an alternative to treatment with chloramine-T. The optimal concentration of hydrogen peroxide depended on the number of treatments, the time intervals between them, and the stage of the disease. When administered as two treatments at 48-h intervals, 250 mg hydrogen peroxide/L was more effective than 10 mg chloramine-T/L. The effectiveness of 100 mg hydrogen peroxide/L was more variable, but treatment consistently and significantly reduced percent cumulative mortality (PCM) compared with untreated control groups; treatment with 25 mg/L was less effective. Clearance of gill-associated F. branchiophilum antigen was greatest with chloramine-T or 250 mg hydrogen peroxide/L; 100 mg hydrogen peroxide/L was again more variable. Three 1-h static baths at 24-h intervals reduced the concentration of hy...

Comparison of Formalin and Chloramine-T for Control of a Mixed Gill Infection (Bacterial Gill Disease and Ichthyobodiasis) in Rainbow Trout

Abstract Juvenile rainbow trout Oncorhynchus mykiss suffering from a mixed gill infection caused by Flavobacterium branchiophilum and Ichthyobodo necatrix were treated with a daily 1h formalin (0.167 mL/L) or Chloramine-T (10 mg/L) bath on each of three consecutive days. Neither formalin nor Chloramine-T completely removed both I. necatrix and F. branchiophilum from infected gills. Analysis of variance (P = 0.01) indicated that formalin treatment was most effective for I. necatrix, which correlated with an improvement in the: Clinical course of disease, but more formalin-treated fish died during the first few days than did Chloramine-T-treated fish following treatment. Both formalin and Chloramine-T significantly reduced cumulative mortality, compared to mortality of control (untreated) fish. Cumulative mortality was lowest among the Chloramine-T-treated fish, but this difference was not significant. After the third treatment, only formalin significantly reduced the number of I. necatrix on the gills (com...

Blood chemistry and acid-base balance in rainbow trout Oncorhynchus mykiss with experimentally-induced acute bacterial gill disease.

Rainbow trout were experimentally infected with the causative agent of bacterial gill disease (BGD) (Flavobacterium branchiophilum) via bath challenge. All fish were cannulated with dorsal aortic catheters, had nasogastric tubes sutured in place for feeding, and were maintained individually, in plexiglass boxes with a flow-through water system. Fish were either fed, or unfed during the trial. Acute changes in blood gas, serum biochemistry and clinical parameters were monitored. By 24h post-challenge, BGD-infected trout that had been fed had significant hypoxemia, hypercapnia, increased blood ammonia, hypoosmolality, hyponatremia, hypochloremia, and increased cough and respiratory rates when compared to control levels. Unfed BGD-infected trout had similar, but less severe blood gas and clinical changes, and no electrolyte disturbances. The BGD-induced hypoxemia is likely exacerbated by increased oxygen demands brought on by feeding. It is not known what association feeding has with the development of low serum ion levels in BGD-infected trout. This is the first study to report the use of fed fish, as opposed to unfed or starved trout, in obtaining blood chemistry values from indisturbed and cannulated animals.

Pathology associated with meningoencephalitis during bacterial kidney disease of salmonids.

The neural pathology associated with spontaneous cases of bacterial kidney disease (BKD), in five species of commercially reared salmonids, was investigated histopathologically and with immunofluorescence. Patterns of localisation of the causative organism of BKD within the central nervous system suggest that haematogenous spread to the meninges, particularly the tela choroidea posterior, the tela choroidea and vascularised capsule of the saccus dorsalis and epiphysis of the epithalamus, and the saccus vasculosus of the hypophysis, appears to be a frequent route by which the central nervous system becomes infected. Retrograde extension from the posterior uvea to the floor of the diencephalon along the epineurium and perineurium of the optic nerve also may be a mechanism of neural invasion. Extension appeared to occur from these sites into adjacent areas of the meninges, the neural parenchyma and ventricles. Demonstration of bacteria within salmonid ependymal cells, as well as the apparent ability of salmonid ependymal cells to respond metaplastically suggest a similarity to mammalian type III ependymal cells (tanycytes). Based on this study, it is apparent that teleosts can survive protracted severe brain damage. This, combined with the apparent similarities of neural response to infection between the salmonids used in this study and higher vertebrates, suggests that teleosts may be a useful lower vertebrate model for studying the pathogenesis and sequelae of bacterial meningitis.