Concentrations of iron, copper, zinc and selenium in liver of Atlantic salmon Salmo salar infected with Vibrio salmonicida

Abstract

Lethal infections with Vlbno salmonicida result in a significant reduction in liver concentrations of iron, copper, and selenium expressed as mg kg' wet wt liver. Infections also increase liver weight as the hepatic sonla t~c index (HSI) is higher in dead and moribund fish than in survivors and non-infected fish. The net result is that total liver content of these minerals is not significantly d~fferent between healthy and diseased, experimentally Infected fish. Hitra Disease is a significant disease problem in Norwegian fish farming. While some authors suggest this is a complex multifactorial disease syndrome resembling vitamin E/selenium deficiency in domesticate animals (Fjdstad & Heyeraas 1985, Poppe et al. 1985, 1986), others (Egidius et al. 1981, 1984) emphasize the importance of a Vibrio sp. frequently isolated from fish suffering from Hitra Disease. This Vibrio sp. can produce the clinical signs of Hitra Disease in challenge tests (Hjeltnes et al. 1987) and has been proposed as a new species, Vibrio salmonicida (Egidius et al. 1986). Hapatic levels of iron, copper, zinc, and selenium have been reported to be much lower in farmed Norwegian salmon than in wild salmon, and fish suffering from Hitra Disease have levels that are even further reduced (Poppe et al. 1986). Several authors have viewed this as support for the hypothesis that nutritional and/or metabolic disorders are important components of Hitra Disease. The data suggest 2 opposing hypotheses: infection of fish with Vibrio salmonicida may be secondary to tissue deficiency of these rninerals, the deficiency actually enhancing susceptibility to the bacterium; or, reduced tissue levels of trace elements may be a result of infection with the bacterium. This study was undertaken to investigate the latter