Íslenskar landbúnaðarrannsóknir - 01.09.1976, Page 22

20 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
Table 1
Groups Tagged ín 1971 and Recaptures by Electric Fishing
Group number Age of smolt in years Number of weeks in outdoor ponds Number of smolts released Number of smolts caught by electric fishing Percent caught by electric fishing
i i 8 2261 (C) 299 13.2
2 i 10 6086 (F) 943 15.3
3 i 12 2989 (C) 440 14.7
4 2 0 448 (F) 55 12.3
5 2 10 583 (C) 58 9.9
6 2 35 2481 (C) 2 0.08
7 2 35 1294 (C) 2 0.15
C 31 Carlin tag
F * Finclipped
enables migrants to react to the proper stimuli
at migration time (Baggerman 1960). Usu-
ally the one-year-smolts being produced at
the Fish Farm were under an intensive rear-
ing program, being fed day and night and
thus being exposed to „constant light" photo-
period. Coupled with the fact that the smolts
did not get very silvery at migration time,
even if they were 17—18 cm long, it was
not unreasonable to assume that the fish
were also physiologically mixed up at that
time.
Saunders and Henderson (1970) found
that reciprocal photoperiod in the spring af-
fected the condition of smolts and reduced
subsequent growth in salt-water. It is there-
fore a reasonable assumption that any other
abnormal photoperiod regime would have
similar effect.
It was decided to try to improve smoltifi-
cation of the one-year-smolts by subjecting
them to natural photoperiod for as long as
needed before release. To do this one had to
sacrifice some of the growth during the
winter when the days are very short but it
was compensated for partly by speeding up
the hatching of the eggs by increasing incu-
bation temperatures and thus lengthening the
rearing period before photoperiod treatment.
One could also expect that the smoltified
salmon would grow very well in the spring
before release as reported by Saunders and
Henderson (1970).
THE 1971 EXPERIMENT
1. Treatment.
The fish used for the 1971 experiment were
hatched under a normal temperamre regime
and started feeding in May of 1970. In early
March of 1971 ca 5000 fish over 13,5 cm
long were Carlin tagged and moved from the