Tony
Bonnie McNeely wrote:
>
> Tony, I'm a little confused. What are non-air breathing fish? Are you referring to fish that breathe by the usual mechanism, gas exchange across gills between water and blood? Those are the only kinds of fishes that I have done critical thermal maxima/minima experiments with, and the only kinds of fishes I have cold euthanized.
>
> When such fishes are cooled slowly, there is no observable stress. There may be stress because the fish are placed in a small, confined vessel without normal visual stimuli, or from handling, but that subsides quickly for most (not all) kinds.
>
> Dave
>
> anutej-in-loxinfo.co.th wrote:
> Thanks for your description of the experiment. What I wonder is that,
> by putting non-airbreathing fish in freezer, whether or not the slow
> drop in temperature would make the fish dies without much stress
> [since the fish does show stressful behavior while temperature drops
> slowly in the experiment]. Obviously when my teacher teaches me about
> dumping fish in freezing water to make them die quickly and painlessly
> I can't believe that simply by watching the fish thrashing around in
> that freezing water.....
>
> Since I had not used chemicals I wonder does fish actually die less
> stressfully than the freeze method by the use of clove oil or other
> chemicals?
>
> Tony
>
> Bonnie McNeely wrote:
> >
> > 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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