I also think that generally the temperature change that is not too
sudden usually allows fishes to adapt and tough it out, and is
probably not too stressful. It is far different from condition in
freezer though where the water temp drops much more quickly.
I know that formalin is a very bad thing to put life fish in. I use
it to preserve fish after euthanized though [for my study].
What I mean about airbreathing fish vs non-airbreathing fish is that
bettas [airbreathers] seem to suffocate before euthanized, even with
access to air. I guess some hardier airbreathers would become
euthanized in the freezer before suffocation from inability to reach
up for air.
If the fish try to avoid things that can endanger their life I guess
they have something that is more or less the same as our fear or
displeasure ^_^ Anyway since the "pain" seems unavoidable I guess the
most humane way is just make the kill quick and least stressful.
Chemicals seem to be the best way in this case...
Bonnie McNeely wrote:
> In the northernmost reaches of the bowfin's range, water does reach zero degrees, and freezes. I know nothing of the biology of bowfins in such habitats. I suspect they are inactive in the unfrozen habitats they almost certainly seek at such times.
> Some kinds of fishes in northern climes are known to actually freeze onto the underside of ice in winter -- Alaskan blackfish for example, and to be perfectly ok when the thaw arrives in the spring. At least textbooks report that as true; I've nat witnessed it. Salt water cold climate fishes have chemical antifreezes in their body fluids as an adaptation to the low temps of their habitat, where the salt in the water prevents it from freezing at temps slightly below the freezing point the fishes fluids would have without the special chemicals.
> But for cold euthanasia, we are talking about dropping the water temp much more quickly than a natural water body temp drops as winter comes on. For physical reasons, the large water body temp drops much more slowly than the air temp, as you know. Consequently, extrapolating laboratory acclimation experiments to nature, fishes acclimatize to the oncoming winter, and they aren't killed, unless cold conditions arrive much more suddenly than is usual.
> I did see fish killed by sudden cold snaps in S. Texas, but except for one time, all the dead fish I saw from that cause were tropicals that had become local pests -- mainly blue tilapia. One time I saw a wide array of local native fish killed from sudden onset cold. That was in December 1969, when the air temperature went from 81 F (27 C) to 16 F (-9 C) in 16 hrs. Water temps dropped from around 75 F (24 C) to 37 F (3 C) in 24 hrs, and fish were not able to escape to warmer water. The Texas Parks and Wildlife Department gave local people dispensation to pick up cold killed game fish from the shores. Birds were feasting. The event put a hit on several game fish populations, but non-game fish aren't monitored.
> anutej-in-loxinfo.co.th wrote:
> Correction: for air-breathing fish I mean labyrinth fish and the like
> [bettas, gouramies, etc]. Can northern species of snakeheads and
> bowfins do fine in 0'C water [freezing water but not yet freeze - not
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