Fiskevelferdsmessig vurdering av produksjon av 0-års smolt

There is substantial data supporting the observation that there is a clear correlation
between fish size during vaccination and adhesions in the abdomen. 0+ fish are
usually vaccinated at a smaller size and at a higher temperature than 1+ exposing
the 0+ more for the possible side effects of vaccination. The effect is two sided.
Firstly a reduced immune response due to suboptimal vaccination can result in
outbreak of diseases and secondly, vaccinating too late prior to smoltification may
delay the smoltification and transferring to early can result in serious problems for the
fish. Those problems are, as such, not a consequence of the method used for 0+
production. But due to the shorter time used in producing the 0+ there is lesser time
in which to meet the demands of a correctly timed vaccination. This challenge is to
be met with good management
in order to meet the challenges placed by tight
production schedule.
Fish health
All diseases can be defined as animal welfare issue as this indicates reduced ability
to manage some aspects of the external and/or internal environment of the fish.
Infectious Pancreas Necrosis (IPN) is the disease resulting in the greatest numbers
of smolt mortalities, irrelevant of production method, in present fish farming in
Norway. Outbreaks of IPN can result in mortalities of varying degree from slight to
major, eliminating the greatest part of the smoltgroup. Pinheads (chronically ill fish)
are usually found long after the outbreak is over. Both 1+ and 0+ smolts contract this
disease. Little difference is observed between production methods. In order to reduce
the danger of contracting IPN one should avoid mixing fish from many hatcheries,
screen for virulent strains and ensure good smoltification. Avoid second-rate smolts.
Cold-water ulcers are mainly observed in cold temperatures. Transferring fish on low
and falling temperatures seem to increase the rate of infection. Good vaccines have
all but removed the problem. An outbreak results in ulcers of varying sizes followed
by homeostatic problems and secondary infections by other pathogens, healed
ulcers result in scarring tissue and melanin spots in the flesh causing the fish to be
down graded, quality wise, upon harvesting. Due to the time of transfer to sea the 0+
smolts are more vulnerable to this disease. Treatment for coldwater
ulcers is now
rare but in case of outbreak, antibiotics have given good results.
Epitheliocystis is an inflammation of the gills, usually found in smolts in late summer
to autumn. Considerable losses of fish (85%) are reported combined with loss of
growth. Available information indicates
higher prevalence in 1+ smolts. No known
treatment, causal agent unknown.
Transfer of 0+ smolt coincides with the periode when the reservoir of sea lice, larvae
and adults, is at its annual peak. In spite of this, sea lice is not reported as a bigger
problem for 0+ smolts than for 1+. This is, mostly, due to the fact that delicing cages
containing small salmon is easier than is delicing cages of larger
salmon. Thus, this
is considered more of a general problem for in the industry.
Moderate fin rot is a common affliction in fish farming and is not considered a
problem if the fins are allowed to heal prior to transfer to sea. The effect is complex.
Firstly there is the loss of outer defences in terms of skin and mucus – resulting in
increased exposure to pathogens. Secondly there is the influx of ions and the
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