Re: NANFA-L-- cold euthanasia

Bonnie McNeely (bnmcneely-in-sbcglobal.net)
Tue, 29 Aug 2006 13:18:43 -0700 (PDT)

Tony, first of all, with euthanasia, the idea is for the fish to die, but humanely.

What you describe here from your class memories sounds like an experiment to determine critical thermal minimum and/or critical thermal maximum. By either experiment, the objective is to determine, very precisely, the temperature at which an aqauatic animal loses equilibrium and cannot save itself by swimming from a deadly thermal environment to a safe one. The animal is placed in water at its acclimation temperature, adn teh temperature is slowly cranked up or down, in hundredth of a degre increments, while the animal is observed to note specific behaviors. At the end point the animal shows specific responses that have been noted repeatedly. Fishes quiver, their fins lock, the operculae quiver, and the fish may turn from upright. If removed by the experimenter at this point, the fish usually recovers. this description applies to critical thermal maximum. Critical thermal minimum is a more subtle response, the animal ceases all movement.

The experiments don't sound nice in the telling, but they have an important function in working out the biology of particular species, and once were of importance in working with populations that might be exposed to thermal pollution, such as in power plant effluent receiving bodies of water.

Dave

anutej-in-loxinfo.co.th wrote:
For the way you suggest it may not work for air-breathing fishes. I
had tried that with bettas and the result is not good... they seem to
be drown before becoming inactivated... :-(

For slow temp change I remember vaguely about experiment in my bio or
eco class in the US about effect of temp on silversides. Even with
rather slow temp change [1/2 - more than 1 hour] they still show sign
of discomfort [and still died] when temp approach extreme on either
side, but far worse reaction on the warm end.

Tony

Jase Roberts wrote:
>
> Hmmm... Yes, that does sound unpleasant for the fish. The difference here is that Dave's suggesting you put the fish in the freezer with some ambient-temperature water. The water's going to slowly cool and take the fish's metabolism down with it -- so by the time they get to freezing, they're almost completely dormant.
>
> What you're doing is sticking a fish with a fully-active metabolism into freezing water. That means the fish is aware of and responding to the extreme temperature change.
>
> If you need to do that, I'd suggest sticking the fish in a small bag of ambient-temperature water, and immersing fish AND bag into a bucket of ice water. That'll chill them more gradually, so their metabolism will go down and they become essentially unaware of the situation before they get to a lethal chill.
>
> -Jase
>
> anutej-in-loxinfo.co.th wrote:
> > Sorry for being negative but I am not so sure about the thought that
> > freezing is humane and painless, since often when I put fish
> > [headwater cyprinids] in freezing water and ice to knock them prior to
> > setting their fins and preservation they thrash around violently for a
> > few seconds. This may not be pain but I doubt they are not in extreme
> > stress and discomfort for that few second.....
> >
> > Tony
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