Et. Valtonen et Di. Gibson, ASPECTS OF THE BIOLOGY OF DIPLOSTOMID METACERCARIAL (DIGENEA) POPULATIONS OCCURRING IN FISHES IN DIFFERENT LOCALITIES OF NORTHERN FINLAND, Annales zoologici Fennici, 34(1), 1997, pp. 47-59
Diplostomid metacercariae were found at a high prevalence and in large
numbers in the eyes of a wide variety of fish species from widely dif
fering freshwater and brackish water environments in northern Finland.
These parasites were found to infect the following: 21 of 25 fish spe
cies, some of which were marine, studied in the oligohaline, brackish
waters of the Bothnian Bay, Baltic Sea; all nine fish species studied
from a large, oligotrophic lake in NE Finland (Yli-Kitka); and all fiv
e studied fish species in a small, hypereutrophic lake (Kuivasjarvi).
Diplostomids in the lens of the fishes of the Bothnian Bay, studied du
ring two periods extending over seven years, suggest the presence of a
stable and predictable system, despite the extremely narrow transmiss
ion window between the first (snail) and second (fish) intermediate ho
sts. Diplostomids in the lens of fishes from the Bothnian Bay and Lake
Kuivasjarvi predominated (> 50% infection in 14 of 21 species) over t
hose from the vitreous body of the eye in most cases, but were much lo
wer (< 18%) in Lake Yli-Kitka. The situation in the vitreous body was
quite the reverse, since diplostomids in this site predominated over t
hose in the lens in fishes of Lake Yli-Kitka (> 80% prevalences in fiv
e of nine fish species). This difference is considered to be dependent
on differences in the piscivorous bird fauna. The fact that diplostom
id metacercariae accumulated in the fish, together with the lack of an
y real seasonal variation, confirms the longevity of these larvae in t
heir fish intermediate hosts. Thus metacercariae form a reservoir whic
h is mainly responsible for the maintenance of diplostomid suprapopula
tions in these northern latitudes.