Íslenskar landbúnaðarrannsóknir - 01.09.1978, Page 119

AN ANALYSIS OF KOLLAFJORDUR HATCHERY 11 7
Mortality
Ist Stage
Rearing
House
Egg
Hatching
House
Sales |
Brood
Stock
Returning
Adults
) Sale
Wfater
Temperature
Allowable
Rearing
Density
Fish
Size
Feeding
Rate
2nd Stage
Rearing
House
Mortality
f
Outdoor
Ponds
Sales
Release of
2-yr Smolts
Release of
1-yr Smolts
Food
Costs

Fixed
Costs
Net Revenue ^
Fig. 2. Relationship between variables which are important to the net economic impact on the hatchery’s
operation.
and stream water, and the heated waler of
the first-stage rearing house are graphed
in Fig. 3.
Decisions under manager conlrol
There are a number ofvariables which the
manager of this hatchery can control.
These include: how many eggs to hatch,
and at what date to hatch them; at what
density to stock the ponds; at what temp-
erature to maintain in the ponds; when,
and how many fish to be transferred to the
second-stage rearing house, moved out-
doors, or sold; how many fish to become
1-year, and how many 2-year smolts; and
when, where, and at what size the ftsh are
to be released. There are certain con-
straints on all of these decisions, of course,
and generally they are not independent. A
decision made at one point will alter the
options available at another point, often in
a complex way.
Some important biological constraints
are: in order to get the proper photo-
period, fish destined to be 1-year smolts
must be moved into the upper rearing
house by October; fish must reach a size of
at least 12 cm by May, if they are to smol-
tify; and in order to survive the winter,
experience dictates that fish ought to be at
15*