Euthanizing FW Fish

[TwoTankAmin]

I have never had to put down a large fish- i.e adult discus and large clown loaches are my largest fish. I have not had to euthanize these larger fish. But most of the fish I keep are smaller. 5 or 6 inches max. TL and most are smaller.

Having to euthanize a fish leaves me feeling queesy before, during and after. I feel badly having to kill things even when I know it must be done. If I had a pet like a dog or cat etc. I would have a vet do the deed. But I have fish and mostly smaller ones. So I know the responsibility is mine. But that does not make it any easier for me to do.

 

[Naughts]

I have never had to put down a large fish- i.e adult discus and large clown loaches are my largest fish. I have not had to euthanize these larger fish. But most of the fish I keep are smaller. 5 or 6 inches max. TL and most are smaller.

Having to euthanize a fish leaves me feeling queesy before, during and after. I feel badly having to kill things even when I know it must be done. If I had a pet like a dog or cat etc. I would have a vet do the deed. But I have fish and mostly smaller ones. So I know the responsibility is mine. But that does not make it any easier for me to do.

This is a wholly understandable stance. If death is accepted easily, we are definitely in the wrong hobby.

 

[Ceez]

You can read the full paper for the first one listed above: https://www.scielo.br/j/bjb/a/4xZbdnymXTQLMvchbXp76mx/?lang=en

The one thing that seems to be common practice in most of what I read no matter what method one chooses to deliver the final death, one should anesthetize the fish first. I doubt if we have to chase a fish around the tank to catch it, then we move it somewhere hostile to smash it, cut off its head or stab it's brain or use clove oil stronger annesthetic to induce death that the fish did not have an unpleasant experience with no anesthetic used.

But consider this from Wiki:


And then there is this as well from Humane Slaughter: Atlantic salmon


What upset me the most about the experience I reported in my initial post was it was clear to me that when I started to adminiter the initial Clove pit the fish reacted ppoly. It was clearly "not happy." I think this was my fault for not administering the anesthetic dose slowly enough. From what I can tell there is a blance hetween how much clove oil is added and how slowly to do it so there is no discomfort to the fish as there will be some anesthetic effect which we increase as we work up to the full anesthetic dosing.

Another way to put this would be, go slow so you know you know you are not "hurting" the fish before it goes to sleep.

Understand that when professionals have to euthanize a fish they mey use an injection. For most of us this is not an option. If I must put down a fish, I want to do so as kindly as I possibly can.

When we go tuna fishing we use a long, whats like an ice pick and stick it straight into the brain as soon as the fish is decked. Never really thought about euthanizing a fish before this thread though oddly enough. I've always been more barbaric about the process.

And these fish aren't friends, they are food!

 

[TwoTankAmin]

I went to the link for the AVMA Guidelines for the Euthanasia of Animals: 2020 Edition Below is the section on euthanizing fish using Clove Oil. In theory these would be the proper instuctions for the acceptable method for euthanizing a fish using Clove Oil.

(4) Eugenol, isoeugenol, and clove oil. Whenever possible, products with standardized, known concentrations of essential oils should be used so that accurate dosing is possible. Concentrations required for anesthesia will vary depending on species and other factors, but may be as low as 17 mg/L for some species. Greater concentrations (10 times the upper range for anesthesia) will be required for euthanasia. These oils are not very water soluble; injecting the solution through a syringe and fine-gauge needle under the water in the container used for euthanizing is helpful in ensuring dispersal in the water. Fish should be left in the anesthetic solution for a minimum of 10 minutes after cessation of opercular movement. These compounds are equivocal or known carcinogens according to the National Toxicology Program. Some studies in rodents indicate this group of anesthetics may cause paralysis in addition to having anesthetic effects, and analgesic properties are unknown. The FDA strictly prohibits the use of clove oil and eugenol as anesthetics in fish having the potential to enter the food chain, except under Investigational New Animal Drug exemptions. Isoeugenol is a potential carcinogen so human safety in the application of that agent is of concern.

Also, goldfish and other species are able to survive immersion in a lethal dose of anesthetic.

MS 222 at a dose of 400 mg/L has been shown to be ineffective for a few species (eg, Gulf of Mexico sturgeon). A recent study307 demonstrated that use of buffered MS 222 in a 1-step immersion technique was inadequate for euthanasia of goldfish (C auratus), a hypoxia-tolerant species. Results from this study support the recommendation for use of a 2-step method for euthanasia of goldfish and some other hypoxia-tolerant species, including cichlids, with the first step of involving immersion to render the fish unconscious and the second involving application of an adjunctive method (such as decapitation, pithing, or freezing) to complete euthanasia.

What I take from reading the paper, in terms of fish, is that first one must be aware of the nature of the anesthetic and the proper dosing. Second, we must also account for the species and the actual size of the fish.

Most of my fish are what I would describe as small. Only my clown loaches get big, My plecos are all the smaller varieties with a full grown adult of the largest species might get 6 inches TL or more like 4.5_ SL. So I have concluded that the proper way for me to euthanize when needed would be to use the proper dose of clove oil and then to freeze. That way no decapitation or pithing for me.

Incidentally, I had one small pleco that went with me to the the Keystone Clash last Sept. When we were netting out fish for the return trip that pleco had expelled from it's anus a red colred tissue mass that trailed behind it. I had the fish in a tank since then. How it survived I do not know. What trailed behind got bigger and the fish did not grow. I pulled it when I was bagging fish for a recent sale and determined that I needed to put it down. I had it in a specimen container overnight with enough water and a piece of polyfilter.

I was not happy abouthaving to euthanizing it today. Fortuately (for me), it passed over night.