Íslenskar landbúnaðarrannsóknir - 01.09.1978, Blaðsíða 94

92 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
TABLE 3.
Experimental design of 1975 comparisons of smolt types by age, release times, and above- and below-lag-
oon release locations.
Agc Smolt type April 25 May 25 June 25
Above lagoon Below lagoon Above lagoon Below lagoon Above lagoon Below lagoon
Early-photoperiod 2X500 2X500 500
1-year Usual-photoperiod 2X500 2X5001) i 2X500 2X500 2X500 2X500
Late-photoperiod 2X500 2X500 2X500
Usual photoperiod 2X500
2-year Outdoor 2X500 2X500 2X590 2X500 2X500 2X500
Total = 18,680, excluding l)
!) In addition, two replicates of 500 each that received unusually severe handling were released.
major cause of mortality, although disease
no doubt has an effect. Temperatures are
lower in the brook than in the man-made
channel below the lagoon. It was
theorized that a release below the lagoon
might bypass some of the perils and en-
sure quicker migration of the smolts out to
sea. This kind of release was actually
tested with considerable success in the
1973 experiment at the Kollafjörður Fish
Farm (Isaksson, 1976).
It was decided to test these two release
locations, along with the release times for
various groups of smolts, some of which
had been exposed for different lengths of
time to artifícially warmed water. This
made the experiment more complicated
but in some ways more meaningful.
The experiments.
The experimental design is shown in Ta-
ble 3. The experiment consisted of releases
above and below the lagoon on 3 different
release days, April 25 May 25, and June
25. As in previous experiments, the gaps
in the table are due to shortages of smolts
in those particular groups. The smolts
from each group were released where they
were expected to give the most informa-
tion. Thus, the early smoltifiers were re-
leased in April and May, and the late
smoltifiers in May and June. As it turned
out in the analysis, some key groups were
missing, but usually some indications
could be detected.
The smolts used in this experiment
have already been described in an earlier
section. All the smolts were very viable
except for some of the smaller 2-year-out-
door smolts which suffered from fm ero-
sion.
All the microtagging was done by the
same person and supervised by the au-
thors. A length-frequency was taken for
each group of smolts since uniform length
in all groups was impossible to achieve.
The smolts were all dipped in 1:6000
malachite solution after tagging and be-
fore transplantation to an outdoor holding
pond.