Fróðskaparrit - 01.01.1995, Síða 115

EXPERIMENTAL INFECTION OF MACROPLANKTON FROM FAROESE WATERS
119
several fishes (Pálsson, 1983). This distrib-
ution corresponds fairly well with the vast
literature reports of A. simplex in fishes (see
e.g. Grabda 1974; 1976; Platt 1975; Smith
and Wootten 1978). The high levels of the
prevalence of infection in krill-eating fish-
es species like herring, blue whiting and
saithe (see van Banning and Becker, 1978;
Højgaard, 1980, 1988, 1995b) is then most
likely to be explained by infected M.
norvegica. Both Calanus finmarchicus and
M. norvegica are common food resources
of the herring, Clupea harengus, around the
Faroe Islands (Jespersen, 1944). Even if the
most important food of blue whiting is
Calanus finmarchicus, C. hyperboreus,
Thysanoessa inermis and T. longicaudata,
M. norvegica constitutes 6.2 % of the food
(Timokhina, 1974). The cod, Gadus mor-
hua, has also high levels of infection with
A. simplex (Rae, 1972; Young, 1972; Platt,
1975; Hauksson, 1992 ). In mature cod one
major source of infection will be other prey
fishes like the blue whiting (Pálsson,
op.cit.), but M. norvegica is also playing a
very important role in its diet (Astthorsson
and Pálsson, 1987). Experimental infection
of fishes with A. simplex from other infect-
ed fishes has been demonstrated by Smith
(1974) and so most likely also will happen
in nature. In conclusion, heavily infected
fishes as a rule either seem to be infected
through M. norvegica (and possibly Thysa-
noessa spp., too) or through infected fish
prey.
The whales are final hosts in the A. sim-
plex-life cycle. An example, is the fin
whale, Balaenoptera physalus, which in
Davey (1971) is listed as a final host of A.
simplex and is predating on M. norvegica
(Relini et al., 1992 and Melle et al., op.cit.)
Unsolved questions are whether frnal hosts
like baleen whales are infected with A. sim-
plex directly from their main food, krill, or
by accidentally eaten, small fishes.
In summary the results presented here
are intended to contribute with some clues
for further work in the uncovering of the
still obscure parts of the A. simplex life-cy-
cle in the macroplankton. A lot of experi-
mental work still has to be done for to clar-
ify the unknown details and mechanisms of
infection. Future research in this area
should also include systematic examina-
tions of M. norvegica for A. simplex larvae
in various regions of the North Atlantic.
This could provide more detailed explana-
tions of the dynamics and relationships be-
tween the distribution pattems of A. sim-
plex in the euphausiacean intermeditae
hosts and in their different fish predators.
Acknowledgements
I thank the crew onboard “Magnus Heinason” for help
in the catching of macroplankton. I am grateful to the
staff at Kaldbak Marine Biological Station for different
kinds of help during the experiments, especially to
Bjørki Geyti, who kindly and skillfully constructed the
sampling gear and some of the equipment for the infec-
tion experiments. I am indebted to Hjalti í Jákupsstovu,
head of Fiskirannsóknarstovan, and to Paul Aspholm,
Oslo, for reađing and critisizing the manuscript.
The work was supported by the Carlsbeg Foundation
(Carlsbergfondet), The Scientific Foundation (Vísinda-
grunnur Føroya Sparikassa) and The Scientific Founda-
tion for Fishery (Grunnurin fyri Vísindaligum Fiski-
vinnukanningum).