Íslenskar landbúnaðarrannsóknir - 01.09.1976, Page 21

ÍSL. LANDBÚN.
j. agr. res. icel. 1976 8, 1-2'. 19-26
The Improvement of Returns of One-years Smolts
at the Kollafjörður Fish Farm 1971-73
Árni Ísaksson
Institute of Fresbwater Fisberies,
Reykjavík, lceland.
ABSTRACT
This paper is a summary of the work that has been done on smolt quality and improvement at
the Kollafjörður Experimental Fish Farm from 1970 through 1973. It describes the methods used
to improve returns of one-year-smolts from practically nothing in the 1970 Tagging Experiment to
approximately 15% in the 1973 experiment.
This was basically achieved by exposing the smolts to natural photoperiod, either with artificial or
natural light, for 30 weeks before release. It was clear that the previous constant light photoperiod
impaired the migratory behaviour of the smolts and had adverse effect on their physiological state
at the time of migration. This was true for smolts as large as 17—18 cm. This became apparent in
a pen rearing experiment where constant-light photoperiod fish could not withstand direct transfer
to saltwater without considerable mortality, whereas their natural photoperiod counterparts could
stand such a treatment.
It was concluded from these experiments that the production of viable one-year-smolts was now
practical in Iceland and the aim should be to have the bulk of the production one-year- smolts,
using geothermal energy to speed up hatching and advance the feeding period.
Introduction.
During the early years of Kollafjörður Fish
Farm, most of the smolts released were 2 or
3 years old. These gave up to 8,2% returns as
reported by GuðjÓnsson (1970). In 1966
the use of thermal water became more ef-
ficient and a new rearing house made the
production of one-year-smolts practical. This
resulted in a great increase in the number of
one-year-smolts released from the Fish Farm
and in 1969 over 50% were of that age
(Guð JÓNSSON 1970). By 1970 it was quite
clear that the one-year smolts in their present
form were worthless for release as down-
stream migrants although they could possibly
be released into rivers to utilize unused
feeding areas. Two-year-smolts, on the other
hand, were giving excellent return-rates.
It was suspected that the one-year-smolts
could be considerably improved by making
them physiologically ready to migrate to sea.
It has been reported that proper photoperiod
is a very important „priming factor" which