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ABSTRACT. Bacterial kidney disease of salmonid fishes, caused by Renibactenum salrnoninarum, was first reported more than 50 yr ago; nevertheless, large gaps persist in our knowledge of the infectionparticularly in methods for its control. In the 1950's, principal control measures consisted of prophylactic or therapeutic feeding of sulfonamides, which were later supplanted by the antibiotic erythromycin. Chemotherapy has effected some reduction of mortality, but benefits are typically transient and mortality usually resumes after the drug is withdrawn. Some studies have indicated that diet composition affects the prevalence and severity of the disease. Although tests of chemotherapeutants and diet modification have continued, research emphasis has shifted partly toward prevention of the disease by breaking the infection cycle. It is now generally accepted that R. salrnoninarum can be transmitted both vertically and horizontally. Experimental ev~dence indicates that immersion of newly fertilized eggs in iodophor or erythromycin does not prevent vertical transmission. However, the injection of female salmon with erythromycin before they spawn shows promise as a practical means of interrupting vertical transmission. The results of attempts to prevent infection of juvenile salmonids by vaccination against bacterial kidney disease have been disappointing, thus underscoring a basic need for a better understanding of protective mechanisms in salmonids. The recent development of more sensitive and quantitative detection methods should aid in evaluating the efficacy of current and future control strategies.

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An indirect fluorescent antibody technique (FAT) has been developed for serological identification, diagnosis of kidney disease (KD), and detection of subclinical infections of KD. Rabbit or goat antikidney disease serum and appropriately labeled immunoglobulin was found to be specific for the KD bacterium. The technique was superior to examination of gram-stained smears for detection of small numbers of KD bacteria. The test requires approximately 2 h.

A direct fluorescent antibody test (FAT) was developed for detecting Corynebacterium salmoninus, causative agent of bacterial kidney disease. The direct procedure was found to be as specific as the previously described indirect test, and requires only 7 min—about [Formula: see text] as much time—to perform. A comparison of the direct FAT with the Gram stain for sensitivity of detecting the bacterium indicated the fluorescent procedure to be 100 to 1000 times more sensitive. Furthermore, the FAT is highly effective and efficient for screening large numbers of samples.Key words: Corynebacterium salmoninus, detection, bacterial kidney disease, direct fluorescent antibody test