Invasive Species Compendium

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Abstract

Sexual differences in the incidence and severity of ectoparasitic infestation of the brown trout, Salmo trutta L.

Abstract

Hatchery-reared and wild S. trutta were examined for skin ectoparasites during spawning in 1977 and 1978. Eight genera of parasites, comprising five ciliates, one flagellate, one monogenean and one parasitic fungus, were identified, with up to five different genera occurring on a single fish. Sexually mature male fish were more frequently or more severely infested by species of Ichthyophthirius, Gyrodactylus and Saprolegnia than were immature fish of either sex or mature female fish. The differences in parasitism were not correlated with seasonal changes in the mucus-producing potential of the epidermis. These findings are discussed in relation to the defence mechanisms of teleost fish and to some of the endocrine changes that occur in salmonid fish during the spawning season.<new para>ADDITIONAL ABSTRACT:<new para>In Cumbria, England, during 1977 and 1978 the ectoparasites recovered from hatchery-reared and wild Salmo trutta included Ichthyophthirius, Trichodina, Scyphidia, Glossatella, Epistylis and Ichthyobodo (only the first 3 species were recovered in sufficient numbers to be considered). Infection with Ichthyophthirius (not found in wild trout) was significantly more frequent in precociously mature, pre-spawning 1 + male trout than in immature trout, and mature males were more frequently infected than mature females. However there were no significant differences in either frequency or intensity in spawning trout. The prevalence of Trichodina, not found in wild trout, was greater in sexually maturing females than in immature fish. A significant difference was noted in the prevalence of infection between immature male and female fish; this difference, however, did not occur among spawning fish. No significant differences in prevalence or intensity of infection with Scyphidia occurred at any time between immature male and female trout, but the prevalence in mature fish was greater among spawning male than female trout.<new para>ADDITIONAL ABSTRACT:<new para>In Cumbria, England, during 1977 and 1978, the ectoparasites recovered from hatchery-reared and wild Salmo trutta included Gyrodactylus. Sexually mature male fish were more frequently or more severely infected with Gyrodactylus than were immature fish of either sex or mature females.<new para>ADDITIONAL ABSTRACT:<new para>Hatchery-reared and wild trout were examined for skin ectoparasites during spawning in 1977 and 1978. Sexually mature male fish were more frequently or more severely infested by Saprolegnia spp. than were immature fish of either sex or mature female fish. The differences in infection were not correlated with seasonal changes in the mucus-producing potential of the epidermis. These findings are discussed in relation to the defence mechanisms of teleost fish and to some of the endocrine changes that occur in salmonid fish during the spawning season.