“Hi I have a question how do I put a fish to sleep/kill it I have a guppy that has a deformity and it’s bad, but he’s swimming and eating but I feel bad ?”
Doc Johnson answers:
My fiancee hates losing fish too, but when it’s going to be slow – she appreciates me letting the fish go humanely with the least struggle. Smushing such a fish works – however, my fiancee would be appalled and I’d be “in the dog house”.
So let’s talk about freezing. I really like it and there are THREE reasons:
First, they don’t feel it at all. As they chill, their nervous system becomes less and less responsive. They are cold blooded creatures and as they chill, their enzyme / energy / neurotransmissions become impossible. It’s been asserted that the fish feel their blood crystalizing with ice. Nope. No more than YOU would feel your blood freezing crystal-by-crystal. (That, by the time your blood is forming ice crystals, you’re dead)
The second reason I like it is because fish have no “spinothalamic tract” which are the nerve tracts that allow a person’s pain-center to send transmissions from the brain base, up to the cortex of your brain to “subjectify” the pain impulses. People can put pain on a 1 to 10 “pain scale” due to these nervous system gifts. Fish on the other hand feel pain “as pain” and can eat or breed while missing entire appendages, even eyes. They certainly avoid painful stimuli but there’s no such thing as “mind numbing” pain to something without a spinothalamic tract.
And lastly, freezing allows the fish to be dispatched with minimal handling and struggle, in a darkened, calm environment in their own water without chemicals. So, I’ll catch the fish and put it in a plastic Ziploc and set the Ziploc in a bowl that fits in the freezer. And put them in the freezer. Shortly, the fish is chilling below a temperature where their brain even ‘works’ anymore. Ten degrees later, their nervous system is practically inactivated. Ten more degrees later and the fish is dead. Five more degrees and the fish is in solid ice.
Reasonable question: Could you euthanize a Walleye you just pulled out of Lake Michigan in February this way? Answer: Sort of. It’s enzymes are geared (at that point) to survive near-freezing water. So it would not shock out or shut down. If you’re dealing with frosty fish, maybe smacking them would be better.
Oil of Cloves is “just okay” because it upsets the fish (it’s sort of caustic) and it takes a bit of time to actually kill the fish. Some people put them in ‘Oil of Cloves’ and THEN in the freezer. That’s cool.
I’m really sorry about that fish. I’m gonna stick with “Freeze it” with minimal fanfare and handling. And that’s because my fiancee is usually watching hahaha. Doc Johnson
If you’re thinking about mass-euthanasia, and it was me, I’d see if I knew anybody with a walk-in freezer and I’d bag ’em up and put them in that freezer. As far as they’re concerned it’s just another flight to Shitsburgh. But as the water temperatures drop from 70 to near 55 (coming from 70) their metabolism will drop drastically and within another 5 degrees they’ll be slipping from ‘awareness’ into a coma. Another 5-10 degrees widens the spread of temperatures way too fast by 30-35 DF and as they coast down onto 40 DF they’re utterly lifeless and comatose. There’s no “feeling the ice crystals biting into their fin tips” Its basically plain old cold shock and then frozen-solid without a struggle. Issue: Icing fish from a winter pond that have very gradually acclimated to 40 DF. Those fish would just get bagged and their coma would occur much closer to 32 DF but would be complete at that time. Yes you can use OIl of Cloves. I think it’s fine. But the extra step may not be worth it because at the same time you’ll see the fish responding to the somewhat caustic irritant that it is, at least for a minute. To each his own.
Recently, it’s come about that some folks are having to euthanize a LOT of fish which may or may not have been exposed to Koi Herpes Virus. (Story here)
“You can make an ice bath with 3/4 cubed ice, and 1/4 pond or tank water. Move the fish abruptly into the ice bath. Their coma will be swift. Then move the fish into the freezer.”
When you’re doing a retailer-size job I would recommend investing in rather a large amount of ice in a 100 gallon vat and create a stout little ice bath. 2/3rds ice and 1/3rds pond water. Net the fish into this ice bath. Shock will be practically immediate for fish under 12″ and it’s quick and complete. Once the fish are stiff and shocked-out I would bag them en masse and transfer to a freezer. I’ve recommended a baton for fish big enough to actually strike. There is a certain mid-size fish which would appreciate the rapid dispatch of decapitation with a blade large enough and heavy enough to sever the head in one strike. A cleaver comes to mind right at the top of the commissure of the gill cover (operculum)
Talk of Oil of Cloves is nice but somewhat esoteric when it comes to mass-euthanasia in large groups of fish being destroyed to stop a virus from spreading or re-entering the retail resource pool.
Doc Johnson