Fiskevelferdsmessig vurdering av produksjon av 0-års smolt

following loss of homeostasis. Thirdly there is the loss of fin surface. This can impact
negatively on the welfare of the inflicted individual, as it will experience reduction in
the ability to master the cage environment. This is mainly a problem for 1+ smolts
as
this is usually an effect of prolonged exposure to cool water. Upon transfer it is
important to make sure that the fins are healed. Increased
temperature and less
biomass in the rearing tanks are efficient remedies.
Water quality
A complex of meteorological, geological and chemical systems interacting with, and
reacting to, the biology of the fish. Suboptimal water quality reduces the ability of the
fish to maintain homeostasis. The effects vary from minor deviations from normal
physiology to immediate mortality. All deviation from optimal or near optimal water
quality effects the smolt in the same way, that being 0+ or 1+ smolts. The main
difference is in how many times the smolts are exposed to the suboptimal situation.
Some of the problems are seasonal and will then affect one group to a larger extent
than the other. The exposure to iron and aluminium is the main concern for the 0+
smolts smoltifying in the fall. Other parameters such as CO2 can be more of a
problem for 1+ smolts as those are exposed for more episodes of low water flow
(usually during peaks in biomass in the spring and fall). To avoid episodes caused
be
periods of deteriorating water quality continuous monitoring of water quality is
recommended. In case of marginal or periodically
marginal water quality one should
consider to take steps to meet those problems.
On transfer, 0+ smolt meet an environment with shortening days and falling
temperatures, quite unlike the natural environment the 1+ smolts experience. The 0+
smolts can meet the most extreme temperatures in the sea depending on place and
time of transfer. Low temperatures make it difficult for the smolts to adapt to the
marine environment. There is an upper and lower limit for optimal transfer but those
are not clearly defined. The recommendation is that one should not transfer smolts
at
falling temperatures if the temperature is under 6-8° C. The 0+ smolts are at a
greater risk in terms of temperature as one can expect falling temperatures during fall
transfer. It is important to ensure good smolt quality and the fish has the opportunity
to adapt to the new environment prior to low temperatures. It is not recommended
to
transfer fish to low temperatures,
and all handling must be careful as to avoid
damage to mucus and skin.
0+ smolts are transferred into a light period that is quite different from the one 1+
smolts experience. It is common to transfer fish to natural light and introduce
continuous light in early January, but is recommended that continuous light should be
used for a fortnight in order to acclimate the fish to the new environment. This is an
unique problem for 0+ smolts as 1+ smolts are transferred on increasing and natural
light.
Smolts are transported over long distances and during the transport one can meet
with many problems. Due to restrictions or water quality on may be forced to run
with
closed well but, transport with closed wells should be for short time only or on
vessels with sufficient recycling capacity to maintain acceptable water quality. When
running with the well open to the sea one should be aware of brackish water zones
that may inflict serious damage on the fish due to the water chemistry in such zones.
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