Plerocercoids of the cestode Diphyllobothrium ditremum in brown trout Salmo trutta: substantial increase in infection after establishment of European minnow Phoxinus phoxinus

Abstract

This study focuses on plerocercoids of the cestode Diphyllobothrium ditremum in brown trout Salmo trutta from the subalpine lake Øvre Heimdalsvatn in south-central Norway. Salmo trutta was the only fish species in this lake until European minnow Phoxinus phoxinus was registered in 1969. The P. phoxinus population increased substantially in the following years. In contrast with the 1969-1972 period, when plerocercoids of D. ditremum were practically absent in S. trutta, there was a high prevalence and intensity of infection in the 2013 S. trutta samples. Because the life cycle of D. ditremum involves two larval stages, in copepods and salmonids and mature worms in piscivorous birds, such as mergansers and loons, a change in feeding ecology of S. trutta or changes in population densities of copepods, fish or birds might have influenced the infection pattern. No relationships between D. ditremum infection and muscle-tissue δ N signature or Hg concentration were found, indicating that infection is not a result of piscivory or cannibalism. Furthermore, consumption of copepods by S. trutta during summer and autumn was low. On the other hand, the number of piscivorous birds has increased, probably due to the presence of P. phoxinus as a new and numerous prey. An increased number of final D. ditremum hosts may have produced a higher output of cestode eggs, resulting in more infected copepods that in turn are consumed by S. trutta. Indirectly, P. phoxinus may therefore have caused the observed increased infection in S. trutta and thereby imposed further negative effects on S. trutta in high mountain areas.

A paradoxical bias in knowledge about Norwegian freshwater fishes: research efforts during 1980-2020

“…The Eurasian minnow has been studied in different contexts. Most studies are set in an ecosystem context, with focus on predator-prey relationships (Borgstrøm et al 1985, L'Abée-Lund et al 1996 and parasite-host dynamic (Museth 2001, Pettersen et al 2016, Borgstrøm et al 2017. It has been a clear focus on the interaction between the minnow and the native fish fauna, in particular interactions with the brown trout (Lien 1981, Museth et al 2007.…”

Research on Selected Wildlife Infections in the Circumpolar Arctic—A Bibliometric Review

“…(DOCX). References [ 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 ] are cited in the supplementary materials.…”