Fróðskaparrit - 01.01.1995, Page 113

EXPERIMENTALINFECTION OF MACROPLANKTON FROM FAROESE WATERS
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for the exposed and non-exposed groups
(the controls, the number of which were
around 50 % of the exposed specimens).
Results
Useful samples of live macroplankton were
collected at the standard depths with the
MIK-net. However, the highest catches of
live euphausiacea were obtained during the
dark hours of the night at depths 5-10 m.
The best survival was observed at tow
speed 1.5-1.8 knots for 5 minutes.
A considerable mortality for all macro-
plankton species ocurred at sea. Under lab-
oratory conditions there was considerable
variation of the mortality in different spe-
cies (Table 1). For instance the crustaceans
survived up to almost three months, while
the molluscs and the chaetognaths only sur-
vived for a few days. On death, Sagitta ele-
gans suddenly tumed to a sort of jelly, mak-
ing it impossible to search the animals for
live Anisakis-larvae. None of the controls
were infected naturally and so they are not
included in Table 1, which shows the re-
sults from the infection experiments, where
macroplankton were exposed to live
Anisakis-larvae. Neither Calanus fin-
marchicus nor C. hyperboreus could be in-
fected. The trials with Parathemisto sp.
were negative, too. Of the two euphausi-
aceans Thysanoessa sp. and Meganyc-
tiphanes norvegica, only the latter could be
infected sucessfully ( 2 out of 8 examined,
or 25 %). Of the molluscs three of the eight
Spiratella retroversa (38 %) were infected,
but not Clione limacina. The chaetognath
Sagitta elegans were not infected either.
The two successfully infected macro-
plankton species contained non-exsheathed
Anisakis-larvae {Meganyctipanes norvegi-
ca) or both exsheathed and non-exsheathed
Anisakis-larvae (Spiratella retroversa). The
length of these larvae did not appear to ex-
ceed those of the larvae outside the host, in-
dicating that no growth seemed to take
place in the time intervals of the experi-
ments. Molting of the euphausiacea was
not observed. Because of a low number of
live animals neither the precise time of in-
fection could be established, nor the time to
an expected exsheatment.
Species Number examined Number infected Survival time (days)
Crustacea: Calanus finmarchius 82 0 12-60
Calanus hyperboreus 10 0 6-70
Thysanoessa sp. 15 0 4-35
Meganyctiphanes norvegica 8 2 10-76
Parathemisto sp. 10 0 8-31
Mollusca: Clione limacina 2 0 1- 3
Spiratella retroversa 8 3 2- 5
Chaetognatha: Sagitta elegans 2 0 1- 3
Table 1. Infection experiments with macroplankton
from Faroese Waters, kept together with newly hatched
Anisakis simplex. larvae. The survival time is recorded
after the retum to land.
Discussion
The present study showed that experimen-
tal infection with newly hatched Anisakis
simplex larvae is possible with two species
of North Atlantic macroplancton: the
opisthobranch mollusc Spiratella retrover-
sa and the euphausicean, Meganicthypanes
norvegica. The infection of S. retroversa
may be a blind route result, because it feeds
on phytoplankton (Ockelmann, 1994).
However, the role of S. retroversa as a