The occurrence of cestode larvae in brown trout after stocking in a large regulated lake in northern Finland

Abstract

The aim of this study was to obtain relevant information on larval cestode infection of brown trout Salmo trutta m. lacustris, for fish stock management purposes in the large, regulated Lake Inari in northern Finland. Compensatory stockings of brown trout have been carried out annually since the mid-1970s. A total of 209 brown trout, which were stocked at the age of 3 yr. were studied for larval cestodes in 1994 and 1995. Diphyllobothrium dendriticum was clearly dominant among the 4 cestode larval species found. The other species were D. ditremum, Triaenophorus crassus and T nodulosus. After 1 summer in the lake the prevalence of D, dendriticum infection was 75% (abundance 5.3) and 46% (abundance 0.9) m 1994 and 1995, respectively. After 3 or more years in the lake (>6+) every brown trout was infected with a mean number of about 130 larvae for both years. All organs in the body cavity were found to be infected. In addition, capsules containing D. dendriticum were found in muscles after the second summer in the lake and the prevalence of muscle infection was 73% (abundance 3.2) and 95% (abundance 7.1) in the oldest age group (26+) in 1994 and 1995, respectively. This has decreased the commercial value of the brown trout. A slight positive correlation between the number of D. dendriticum and the condition index (Fulton) of fish was found in each age group, although histological stud~es of heavily lnfected fish revealed severe chronic granulomatous peritonitis. Indications of el~mlnation of individuals most heavily parasitized with D. dendriticum were not obtained for the present material. D. dendriticum was not found in the potential prey fishes of the brown trout studied in Lake Inari: vendace Coregonus albula, whitefish Coregonus sp. and nine-spined stickleback Pungitius pungitius.

Accumulation of plerocercoids of Triaenophorus crassus in the second intermediate host Coregonus lavaretus and their effect on growth of the host

“…This in its turn would expose fish to more parasites and increase accumulation rate, but is not seen as increased fish growth. Increased rates of food consumption of infected hosts have been demonstrated earlier for sticklebacks Gasterosteus aculeatus L. harbouring Schistocephalus solidus (Walkey & Meakins, 1970;Milinski, 1985;Giles, 1987) and suggested to be the reason for a positive correlation between the number of parasites per fish and Fulton's condition index of brown trout Salmo trutta m. lacustris L. infected with Diphyllobothrium dendriticum plerocercoids (Rahkonen & Koski, 1998).…”

Effect of marine Eubothrium sp. (Cestoda: Pseudophyllidea) on the growth of Atlantic salmon, Salmo salar L.

“…Larval cestodes elicit an immune response in their hosts. Diphyllobothrium dendriticum encapsulated on visceral organs have been observed to generate both cellular and humoral immune responses in the fish (Sharp, Pike & Secombes 1989, 1992; Rahkonen & Koski 1997) and Ligula intestinalis has been observed to induce specific cellular responses in roach, Rutilus rutilus (L.) (Hoole & Arme 1986). However, adult cestodes living in the alimentary tract have generally been assumed to not cause any harm to the host (Rees 1967; Mackiewicz 1988).…”

Effects of fish species composition on Diphyllobothrium spp. infections in brown trout – is three‐spined stickleback a key species?

“…). Two parasite species, Diphyllobothrium ditremum and D. dendriticum , commonly infect brown trout, Arctic charr and three‐spined stickleback in northern Europe (Halvorsen ; Henricson ; Andersen & Valtonen ; Rahkonen & Koski ; Knudsen et al . ; Kuhn et al .…”