Occurrence of the digenean Cryptocotyle lingua in farmed Arctic charr Salvelinus alpinus and periwinkles Littorina littorea sampled close to charr farms in northern Norway

Abstract

Occurrence of Cryptocotyle lingua rediae was recorded in periwinkle samples collected adjacent to 10 charr farms and at control sites 1 to 5 km from the farms. In 7 out of 10 localities the prevalence of infection was higher in the sample taken adjacent to the farm than in the control, and overall prevalence was 13.7 O/O in periwinkles near the farms and 6.1 % in snails from the control sites, a highly significant difference. Prevalences in periwinkles close to farms tended to increase with duration of farming at the site. The role of the final host, piscivorous birds, is considered Samples of charr from 11 farms were investigated for visible black spots caused by encysted C. llngua metacercariae. No infected charr were recorded in the 2 land-based farms where seawater exposed to UV-light (photozone) was pumped to the tanks, whilst 83.2 '10 of the fish exhibited black spots in the 9 farms where the charr were stocked in floating net cages in the sea. In most infected fish the C. ljngua cysts were located only on the fins in relatively small numbers.

Controls of Spatial Variation in the Prevalence of Trematode Parasites Infecting a Marine Snail

“…Biological factors included the abundance and diversity of birds (the dispersive vector for the trematode eggs), crab, fish, and snail species. Positive associations have been suggested and sometimes shown between trematode prevalence in snails and the density of (1) definitive hosts (Smith 2001, Hechinger and Lafferty 2005, Fredensborg et al 2006), (2) intermediate hosts (Kristoffersen 1991, Hechinger et al 2007, and (3) the snail hosts themselves (Ewers 1964, Wilson andTaylor 1978). For certain snail and crab species, we also recorded size and biomass measurements.…”

Variations in juvenile growth, energy allocation and life‐history strategies of two populations of Arctic charr in North Norway

“…(ii) Smolts: descending fish with smolt characteristics (Damsgård, 1991;Staurnes et al, 1992) that were not infected by marine parasites (Kristoffersen, 1991;Kristoffersen et al, 1994), and not previously caught in the traps in the outlet streams.…”

The relationships between anadromy, sex ratio and parr growth of Arctic charr in a lake in North Norway

“…(ii) Smolt: descending fish <23 cm in length with smolt characteristics as defined by Damsgård (1991) and Staurnes et al (1992). The 23-cm limit was set because no descending fish under this size were infected by marine parasites, which identifies sea-run charr (Kristoffersen, 1991;Kristoffersen et al, 1994). Most of the descending charr classified as smolts were larger than 23 cm after the sea-run.…”