Showing papers by "Rune Knudsen published in 1997"

Parasite communities in two sympatric morphs of Arctic charr, Salvelinus alpinus (L.), in northern Norway.

Abstract: In this study from Fjellfrosvatn, an oligotrophic lake in northern Norway, the parasite communities in two sympatric Arctic charr populations were compared. The dwarf morph, which inhabits the profundal zone, exhibited the lowest parasite diversity, seven species, and 72% of these charr harboured only one or two parasite species. In contrast, 10 parasite species were encountered in the larger normal charr, and between 5 and 8 species were present in 73% of these fish, which also utilised a broader food and habitat niche. Proteocephalus sp. was by far the most abundant species in the dwarf charr, probably because this morph fed intensively upon the benthic copepod Acanthocyclops gigas. On the other hand, parasites that are transmitted with littoral benthic prey (i.e., Phyllodistomum umblae, Cyathocephalus truncatus, Cystidicola farionis, and Crepidostomum spp.) were almost absent in the dwarf charr, though they were common in the normal morph. Also, Diphyllobothrium spp. were more prevalent in the normal c...

Infection of Salmincola edwardsii (Copepoda: Lernaeopodidae) in an age‐structured population of Arctic charr—a long‐term study

Abstract: The parasite-host relationships between Salmincola edwardsii (Copepoda: Lernaeopodidae) and Arctic charr Salvelinus alpinus were studied in lake Takvatn, northern Norway, over an 8-year period. The infection levels were modest, with an overall prevalence of 16·1% and an abundance of 0·5 parasites fish−1. Most of the infected fish (54·1%) had only one parasite attached, whilst only 4·3% had more than 10. In general, parasite infection increased with increasing age, and hence size of the fish. The increase was modest up to age 7, whereafter a steep increment in parasite burdens occurred. Within each age class there was little effect of either fish size, gender, maturation or choice of macrohabitat upon parasite abundance. There was also little year-to-year variation in infection of the different age classes, indicating a high degree of stability of the parasite-host interactions in this system. The infection levels exhibited seasonal changes, being lowest in early summer and highest during winter. The infection rates seemed to be related to seasonal and ontogenetic habitat shifts of the charr.