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  • 1990-1994  (3)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 45 (1994), S. 0 
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Furunculosis was first discovered in a fish farm in Norway in 1964, following the importation of rainbow trout from Denmark. The disease spread to several farms and to wild fish in the River Numedalslågen, occurring there until 1979. It was eradicated at several farms, the last being disinfected in 1969. In 1985, furunculosis was discovered in marine fish farms in Nord-Trøndelag, following importation of salmon smolts from Scotland. The disease reached Møre og Romsdal in 1988, by which time 32 fish farms were infected in the two counties. By the end of 1992, 550 farms were infected. The disease spread concurrently in natural watercourses, from 22 in 1989, to 74 by the end of 1992. Rapid spread of the disease was associated with several factors including escapes from fish farms, possibly via transport of fish between farms, and natural movement of wild fish in the sea. The disease was not associated with particular physical characteristics in these watercourses, but large aggregations of fish beneath waterfalls combined with high water temperature may trigger disease outbreaks. The ecological consequences of furunculosis are not known. However, some river populations of adult salmon, sea trout and brown trout have suffered. Furunculosis may result in serious negative consequences for populations if a significant number of the brood stock die before spawning.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 40 (1992), S. 0 
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Gyrodacrylus salaris was most probably introduced to the River Lakselva in 1975 through stocking of Atlantic salmon from an infected hatchery. The parasite population grew rapidly, and the parasite spread throughout the entire watercourse during the summer of 1976. This epidemic situation led to mortality among the young Atlantic salmon, and the density of salmon parr was heavily reduced from 1976 to 1977. The density of salmon parr has remained close to zero since then, while there are no apparent trends toward decrease or increase in the density of brown trout. In spite of the reduced density of young salmon, a new epidemic has developed each year among the few young 0+ and 1+ Atlantic salmon present in the river. Results from successive sampling during the summer of 1987, 1988 and 1989 indicate that most of the presmolt salmon are attacked during their first summer or autumn of life. The infection develops into an epidemic during the first autumn, winter or the next summer. The build-up of the parasite burden on the fish leads in turn to mortality. Norwegian Atlantic salmon probably have no resistance against G. salaris, since the parasite has recently been introduced to Norwegian rivers.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 42 (1993), S. 0 
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We investigated the influence of variation in body size and growth rate on age of smolting in Atlantic salmon and brown trout in four different Norwegian rivers. In Atlantic salmon smolt ages varied between 2 and 6 years, and in brown trout between 2 and 7 years. Smolt age was negatively correlated with parr growth, and positively correlated with smolt size. Age at smolting was more variable in the two northern than the two southern rivers. Smolt sizes and ages were also more variable in brown trout than in Atlantic salmon. Based on the observed variation in smolt size and age, we reject the hypothesis that a threshold size alone regulates age at smolting. Within populations smolt age depends on growth rate so that fast-growing parr smolted younger and smaller than slow-growing parr. We hypothesize that smolt size and age is a trade-off between expected benefits and costs imposed by differences in individual growth rate.
    Type of Medium: Electronic Resource
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