Euthanasia/culling is always a touchy subject, however I think the majority of responsible fish keepers and certainly the academic/scientific community all agree that it does become necessary to cull or destroy certain fish in certain circumstances.

This of course forces us to ask the question:

"When it does become necessary, what is the most humane way to kill a fish?"

I have heard many opinions and methods discussed. For some reason "clove oil" keeps coming up. I have only found ancedotal evidence to support clove oil as being "humane". What is the exact method by which clove oil acts?

Rotenone is certainly effective, but I don't believe it to be the "most humane" way to cull.

Rotenone works by inhibiting a biochemical process in the fish cells, resulting in an inability of fish to use oxygen in the release of energy during normal body processes. In effect, the fish suffocate due to lack of oxygen. But, contrary to popular belief, rotenone does not remove oxygen from the water. Fish treated with rotenone move to the shallow water or to the surface of deeper water, gasping for oxygen within a few minutes of exposure to the chemical.

Sounds like suffering to me.

I have found several references to MS-222 "Tricaine" and it sounds like a good option as Tricaine is an anesthetic not just a toxin. From the Merck Veterinary Manual

Tricaine methanesulfonate (MS-222) is FDA approved for use as a sedative and anesthetic in food fish and is often used to sedate broodstock for handling and injection of hormones for spawning. It is also useful for pet fish and is effective for sedation, surgical anesthesia, and euthanasia. Sedation can generally be achieved with concentrations between 50-100 mg/L, although species-specific sensitivities should be expected. Induction for most species may be near 125 mg/L; however, when working with unfamiliar species it is best to start at a lower concentration (ie, 50 mg/L) and increase the concentration until the desired effect is achieved. Because MS-222 is an acid, the chemical should be buffered (2 parts sodium bicarbonate by weight to 1 part MS-222). Following induction, the concentration may be decreased to 50-100 mg/L to maintain the desired depth of anesthesia. Respiration should be monitored; if opercular movement ceases, fish should be immediately moved to clean water. MS-222 can also be used to euthanize fish at concentrations of 1,000-10,000 mg/L. For small animals, a squirt bottle with a stock solution of 10,000 mg/L can be used to quickly apply a lethal dose of chemical to the gills.

I think Tricaine is a good idea when you need to do a necropsy and don't want to destroy any tissue...but severing the spinal cord and or destroying the brain seems to be the method of choice for scientists/vets...

Now, for those who aren't squeemish, or who don't like using chemicals there is always what I was taught in school: Either decapitation (quick slice/snip behind the eye in front of the dorsal fin straight down severing spinal cord) or by "pithing" AKA direct destruction of the brain may be the "most humane" method.

I personally use Tricaine (MS-222) and freezing if this unfortunate occasion arises.
Tricaine is not however available to all or in all cases and in those cases Swift blunt Head trauma or decapitation are both quick and effective and IMO acceptable.

Swift blunt Head trauma

Translation: Put the fish in a bag and whack it up against the side of the house. Mind you don't get splattered!

P.S.: This really works.

I'd swear there was a long thread about this several months ago, but I can't find it right now. Does anybody recall this, and can somebody post a link to the thread?

Yep, I remember that topic. The thread became nasty and convoluted. I Was a lurker then. I have since taken a quick sharp knife to the fish that had to go. Same as my fish for food technique.

One of my graduate advising professors at the University of Wisconsin - Milwaukee, Dr. Timothy J. Ehlinger, did some extensive research on this very subject about 12 years ago when I was at university there. The most humane way that he found to euthanize fish was to put them in a water-tight container and simply put the container in the freezer. He said that the fish's metabolism slows down and eventually the fish just "goes to sleep". Obviously, if you're using the fish for scientific purposes, you remove the container and fish before it becomes a solid block of ice. Ninety-nine percent of the time the fish has "passed-on" before this point. This is the method I use when I have to euthanize a fish or fishes.

The research lab that I volunteer at uses MS-222 as part of their protocol for euthanizing fish.

The freezer method is generally accepted as being OK. Especially for those of us who don't have any MS-222.

Clove oil works too.

Personally, I just whack 'em. Against the side of the house. In a paper bag. Instantaneous.

I've tried severing the spinal cord at the base of the skull and I was not happy with the results.

Clove oil works too.

I'm sure it does...So does Mt. Dew or gasoline! But does anyone know how clove oil kills? Is it simply asphyxiation where no gas exchange happens across the gills, or is it something else?

I'm sure it does...So does Mt. Dew or gasoline! But does anyone know how clove oil kills? Is it simply asphyxiation where no gas exchange happens across the gills, or is it something else?

Clove oil is at the very least an anesthetic. It's used on humans worldwide for this purpose. It might have an additional effect but undoubtedly humane to euthanize fish when administered correctly.

http://afs.allenpres...ues...CO;2&ct=1

If you're technologically competent enough to post on an internet forum, then you should have the ability to do a quick google search (or whatever search engine you happen to prefer). 0.3 seconds later you'd know that the active compound in clove oil is eugenol, you'd have the chemical structure of the compound, and you'd likely have some references as to how it's used.

There's been some discussion over whether it's as effective as MS222 and much argument over whether it is humane; personal observation suggests that overdose relaxes the fish to the point where respiration stops and the fish dies. Seems pretty humane to me. The benefit is you can get clove oil almost anywhere (try local GNC or health food stores for cheapest results, fru-fru aromatherapy shops or fancy supermarkets if you want to pay as much for it as MS222), and you're not driving or flying around with white powder...

The reference below seems interesting but I don't have online access. You could probably get it through your local university library, especially if they have a vet program.

Pali?a, D., D.M. Herolt, C.B. Andreasen, B.W. Menzele and J.A. Roth. 2006. Anesthetic efficacy of tricaine methanesulfonate, metomidate and eugenol: Effects on plasma cortisol concentration and neutrophil function in fathead minnows (Pimephales promelas Rafinesque, 1820). Aquaculture 254(1-4), 675-685

cheers,
Dave

f you're technologically competent enough to post on an internet forum, then you should have the ability to do a quick google search (or whatever search engine you happen to prefer). 0.3 seconds later you'd know that the active compound in clove oil is eugenol, you'd have the chemical structure of the compound, and you'd likely have some references as to how it's used.

I tried that too. Unfortunately I don't have 100's of dollars to subscribe to these journals. The tidbits I did pick up were not illuminating as to the physiological mechanism of the anesthetic effect.

By analysing the chemical structure of eugenol (and it's more effective isomer) and constructing a 3-dimensional virtual model therefrom, I have noticed that it is a good mate for certain neurotransmitters. I hypothesize the eugenol binds readily with these compounds, acetylcholine in particular, thus altering their properties sufficiently to prevent them from transmitting neural impulses.

I prefer, when possible, MS 222 as an anesthetic prior to taking tissues or for whole specimens samples. I rank clove oil fairly low as several of my fisheries friends have said that cortisol levels still increase while under anesthesia with it, but I've never looked up the references so take it with some salt. Cortisol levels are a generally accepted method for determining stress when your study organism doesn't have the ability to say "This sucks!"
I typically put terminally sick fish from my aquariums in the freezer.

OK, here's the range of observed physiological effects of both MS-222 and clove oil (eugenol). In short, the major effect is to lower oxygen content in blood, and to affect the chemical environment of the bloodstream in such a way as to interfere with successful oxygen transport:


Am J Vet Res. 2001 Mar;62(3):337-42.
Comparative efficacy of tricaine methanesulfonate and clove oil for use as anesthetics in red pacu (Piaractus brachypomus).Sladky KK, Swanson CR, Stoskopf MK, Loomis MR, Lewbart GA.
Environmental Medicine Consortium, Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh 27606, USA.

OBJECTIVE: To compare the anesthetic efficacy and physiologic changes associated with exposure to tricaine methanesulfonate and clove oil (100% eugenol). ANIMALS: 15 adult cultured red pacu (Piaractus brachypomus). PROCEDURE: Fish were exposed to each of 6 anesthetic concentrations in a within-subjects complete crossover design. Stages of anesthesia and recovery were measured, and physiologic data were collected before and during anesthesia. RESULTS: Interval to induction was more rapid and recovery more prolonged in fish exposed to eugenol, compared with those exposed to tricaine methanesulfonate. The margin of safety for eugenol was narrow, because at the highest concentration, most fish required resuscitation. Mixed venous-arterial PO2 consistently decreased with anesthesia, while PCO2 consistently increased with anesthesia in all fish regardless of anesthetic agent. The increase in PCO2 was accompanied by a decrease in pH, presumably secondary to respiratory acidosis. Anesthesia was associated with increased blood glucose, potassium, and sodium concentrations as well as Hct and hemoglobin. Fish anesthetized with eugenol were more likely to react to a hypodermic needle puncture than fish anesthetized with tricaine methanesulfonate. CONCLUSIONS AND CLINICAL RELEVANCE: Anesthesia induced with tricaine methanesulfonate or eugenol contributes to hypoxemia, hypercapnia, respiratory acidosis, and hyperglycemia in red pacu. Similar to tricaine methanesulfonate, eugenol appears to be an effective immobilization compound, but eugenol is characterized by more rapid induction, prolonged recovery, and a narrow margin of safety. Care must be taken when using high concentrations of eugenol for induction, because ventilatory failure may occur rapidly. In addition, analgesic properties of eugenol are unknown.

PMID: 11277197 [PubMed - indexed for MEDLINE]

If you're technologically competent enough to post on an internet forum, then you should have the ability to do a quick google search (or whatever search engine you happen to prefer). 0.3 seconds later you'd know that the active compound in clove oil is eugenol, you'd have the chemical structure of the compound, and you'd likely have some references as to how it's used.

Ok... You are right, I'm being lazy...I could have googled it...Then again, one can pretty much google anything and get some kind of answer...I was looking for a discussion amongst informed and knowledgeable people like yourself. I appreciate your answer.

and you're not driving or flying around with white powder...

BWahahahah!LMAO...Really good point...I could just see the eyes of an airport security person getting getting wide..."anthrax?...heroin?...cocaine?"..."No, I use it to put fish to sleep"...

Clove oil is at the very least an anesthetic. It's used on humans worldwide for this purpose. It might have an additional effect but undoubtedly humane to euthanize fish when administered correctly.

http://afs.allenpres...ues...CO;2&ct=1

I have access as a subscriber to that article if we are trying to have it posted.

By analysing the chemical structure of eugenol (and it's more effective isomer) and constructing a 3-dimensional virtual model therefrom, I have noticed that it is a good mate for certain neurotransmitters. I hypothesize the eugenol binds readily with these compounds, acetylcholine in particular, thus altering their properties sufficiently to prevent them from transmitting neural impulses.

Yah, I came to the same conclusions, both on the chemical structure of eugenol. , and the put 'em in the bag and whack 'em technique.
The blunt force trauma is instantaneous. No time even to feel fear or stress as when swimming in the freezer or breathing in chemicals.
Having been at the recieving end of some blunt force trauma myself, I know you don't feel a thing until you wake up. Therefore, no wake up, no pain.
Wow, this forum is pretty mature to handle this politically incorrect topic so calmly. Imagine bringing this up on the mainstream aquarium forums?
Kinda like when somebody posted on the python forum that he was looking for free kittens to feed his snakes.

I use the blunt force to euthanize my fish. I have a book here that says to never put a fishin the freezer because it affects their capillary blood vessels just under the skin and it causes the fish great pain before it loses conciousness. I don't know if this is true but it definatly doesn't sound humane. I just whack 'em and its all over!

Wow, this forum is pretty mature to handle this politically incorrect topic so calmly.

Well, it has been pretty well hashed out over the years. Sufficiently so that nobody raises an eyebrow at the thought of "whacking" a fish

I'm surprised nobody recommended the Amia calva solution to this.