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Most respondents agreed that a water temperature fluctuation of between
l'C and 3'C was acceptable. Of 20 respondents, 13 monitored water temperature
in the anaesthetic bath, and most hatcheries reduced the temperature simply by
changing the anaesthetic baths frequently. Of 19 respondents, seven hatcheries
measured dissolved oxygen levels at least occasionally and nine used oxygenated
anaesthetic baths.
It was recognized that anaesthetic dosages varied with
temperature, but only 5 of 19 hatcheries buffered the anaesthetic even though
the pH often dropped below 7.
When asked about actual human health problems associated with fish
anaesthetics, five hatcheries reported that such problems existed.
Both the
2-phenoxy and MS-222 were implicated in causing skin rashes, some acne and
possible other effects on pregnant workers. Health concerns were most often
cited as the reasons why a certain anaesthetic was not used, and workers were
primarily concerned about skin rashes and unknown carcinogenic effects.
Marking Technique
All of the surveyed hatcheries used disinfectants (iodinefbromine based)
during tagging, but 6 of 19 hatcheries did not disinfect between different groups
of fish within the hatchery. At approximately half of the surveyed hatcheries,
fish were treated after marking, usually with a malachite dip. However, six of
19 respondents reported infection after marking, even among treated groups of
fish. The infection incidence was usually 1% or less of the marked population.
One third of the surveyed hatcheries attempted handling smolting fish and in most
cases problems developed even at relatively low water temperatures (8'C - 9'C).
Holding and mixing strategies differed for different species but most
marked fish were held for no more than 3 - 7 days before remixing. In 11 of 19
hatcheries, marked fish were remixed with unmarked fish, often immediately upon
recovery from the anaesthetic or within 1 or 2 days of marking. Information on
long-term tag retention was available for nine of 21 hatcheries. The general
comment was that if tagging was done properly, the long-term tag retention should
be stable.
Most respondents considered a desirable holding period before release to
be approximately two weeks for all species. This would allow the fish to recover
from tagging stress. However, in many cases marked chum fry were not held long
enough before release. This was because of the short time interval between the
time when the fry reached a proper tagging size and the time for release.
Duality Control
All hatcheries employed their own staff to perform quality control checks
throughout the marking operation, even when a contractor also performed quality
checks. The frequency of checking varied from 100 fish once daily, to 10 fish
five times daily, etc.
The majority of clip-checking involved a "vial"
inspection (84%) rather than a microscope (16%).
Of 18 responses, six had
information on fin regeneration.