Fróðskaparrit - 01.01.1995, Síða 114

118
EXPERIMENTALINFECTION OF MACROPLANKTON FROM FAROESE WATERS
transport host is a possibility requiring fur-
ther examination. The finding of infected
M. norvegica appears to be the first report
of an experimentally infected euphausiacen
in Europe. In Japan Oshima et al. (1968)
and Oshima (1969) experimentally infected
Euphausia similis and E. pacifica with
newly hatched Anisakis-larvae, but the eu-
phausiaceans could not survive longer than
eight days. In the present experiments the
difficulty of keeping the euphausiaceans
alive is a problem, too, but the animals
could be kept for 2-2 1/2 months.
The experimentally infected macro-
plankton M. norvegica seems to confirm
the work of Smith (1971). He reported one
1.9 mm Anisakis-líivv'ác in M. norvegica
from the northern North Sea, indicating
considerable growth from the length of
non-exsheathed larvae of 0.22-0.29 mm.
Sluiters (1974) reported positive correla-
tion between infection with Anisakis and
the euphausiaceans M. norvegica, Thysa-
noessa inermis and T. raschii from stomach
investigations of herring from the North
Sea. Smith op.cit. also reported two species
of euphausiacea, T. inermis and T. longi-
caudata from the northem North Sea and
waters around the Faroe Islands as first in-
termediate hosts of Anisakis simplex. In the
northem North Pacific and in the Bering
Sea Oshima et al. (1969) found Anisakis
type I-larvae (= A.simplex) in T. raschii and
T. longipes. Even if the records of natural
infection of Thysanoessa spp. is thus well
documented in the literature, the present
study could not succeed in infecting them
experimentally. This is posing the question
whether Meganychtiphanes becomes easier
infected in nature than Thysanoessa, as
demonstrated in the laboratory.
How is Meganyctiphanes norvegica in-
fected with Anisakis simplexl Køie (1993)
suggests an infection route from copepods
to euphausiacea, based on experiments
with Acartia tonsa. This could not be veri-
fied by the present experiments with the
copepods Calanus finmarchicus and C. hy-
perboreus, which are of a considerably
larger size than Acartia tonsa. Sluiters
op.cit. found no correlation between cope-
pods in the stomach of herring and infec-
tion with Anisakis.
Beyer (1992) found the main food of M.
norvegica to be Calanus spp., who appar-
ently not are infected with A. simplex. If no
other intermediate transport host are found,
it seems most likely that M. norvegica are
infected directly with newly hatched A.
simplex larvae in the water mass, where this
euphausiacean is making extensive vertical
migrations searching for food both as a car-
nivore and a herbivore (Mauchline, 1980;
Melle etal., 1993).
The question arises, too, in what life
stages Meganyctiphanes norvegica is sus-
ceptible for infection from ingested A. sim-
plex larvae. Most likely infection will occur
in the growth period, which is from March
to August, depending on its three year life-
span (Mauchline, 1977). This requires fur-
ther investigations with smaller size groups
of M. norvegica than used in this study
(adults, close to 40 mm).
The krill species M. norvegica is wide-
spread in European and American Waters
(Einarsson, 1945; Mauchline, 1980). In the
North Atlantic it is a common food item for