Fróðskaparrit - 01.01.1995, Page 112

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EXPERIMENTALINFECTION OF MACROPLANKTON FROM FAROESE WATERS
The sampling gear was the MIK-net, a
macroplankton sampler, working at the
depths 10, 25, 50 m. The mesh sizes were
0.5 mm in the last 2 meters of the net, in the
other 13 meters in front, the mesh size was
1.5 mm. The diameter of the front was 2 m,
the end 15 cm. Towing was performed for
10 minutes at tow speed 2-2.5 knots. The
setting and hauling each required 5 min-
utes. On the second trip a specially de-
signed 11 liter plast cylinder or a 12 liter
square plast sample flask were fastened to
the end of the net in order to enchance the
survival of the macroplankton. Tows were
made at different depths (0 to 50 m), time
of the night and speed (1 to 3 knots) to find
the best way of catching live krill, being
very fragile and vulnerable in the catching
process itself and in the handling follow-
ing.
Experimental infection was carried out
twice, using three different methods of ex-
posure. Larval Anisakis simplex in the fol-
lowing will be referred to as “Anisakis” or
“larvae.”
In the first experiment in April, the
macroplankton were sorted by hand in 200,
500 or 1000 ml transparent plast bottles,
which the day before the trip had recieved a
pippeted dose of 28 Anisakis-hirvae per ml
final volume. Control groups without lar-
vae were maintained under the same exter-
nal condition, the ambient temperature on
deck was 4-8° C in April and in May 6-8°
C.
In the second experiment in May most of
the macroplankton were kept alive onboard
in 30 liter green plast barrels, adding from
time to time gently running seawater. The
rest was sorted out and placed in 200, 500
or 1000 ml plast bottles to which live Ani-
sakis-larvae (28 per ml final volume) were
introduced immediately. Other sets of ex-
periments were started immediately after
retuming to land, at Kaldbak Marine Bio-
logical Station, Faroe Island. The macro-
plankton was kept in closed systems (in the
same barrels or smaller plast boxes), with
continous aeration, no change of seawater
and in dim (red) light, the temperature was
8-10°. Each experimental unit recieved a fi-
nal amount of approximately 1-5 larvae per
ml or none (controls). As the larvae sink to
the bottom where the plankton usually is
situated, the actual exposure of larvae be-
comes far higher than the mean 1-5 per ml.
The larvae were hatched from eggs, col-
lected from mature Anisakis females from
the stomach of the long finned pilot whale,
Globicepala melas, and were isolated ac-
cording to the method of Højgaard (1995a).
The hatching was carried out at tempera-
tures 2°-8° C. The plankton was fed week-
ly with Chlorella sp., cultivated at 20° C.
The survival and activity of the larvae was
checked weekly by taking bottom samples
from the experimental units.
In the infection experiments the mortali-
ty of the Anisakis-larve was close to zero
and negligible the first month, but after
three months the mortality was estimated to
50 %. The macroplankton was dissected
live or shortly after death and searched for
live larvae under a binocular microscope,
magnification 20-40 X. Infection was only
recorded as positive, if live larvae were
found inside the designated host. The mor-
tality and survival were at the same levels