Euthanizing Aquarium Fish


Fish Out Of Water: DOA, originally uploaded by mybluemuse.

Q: TSM wrote,

How do I know when I should put down my betta? He has all the obvious signs of dropsy (bloated abdomen and pine coning scales) and is laying on the bottom of the tank gasping for air. I feel terrible watching him suffer. Which is the best and most humane method for euthanizing my fish?

A: Determining when to euthanize your fish is a very difficult decision to make and one that shouldn’t be made lightly. There are several things to consider before choosing humane euthanization.

When to Euthanize:

1. Do you have a reasonable diagnosis for your fish?

As hobbyists, we rarely have access to scientific equipment to help us determine a diagnosis for our sick fish. Most of us aren’t fortunate enough to have a microscope or other necessities to distinguish between bacterial, viral or parasitic infections. In most cases, we make assumptions based on probability. If your fish has a bloated abdomen and the scales are protruding, it is reasonable to assume he has Dropsy, which is rarely curable in tropical fish like Bettas. The degradation of the fish can be quick or slow with Dropsy and the final stages often leave the fish helpless and gasping at the bottom of the tank. Utilize your recourses to come up with a diagnosis. You can try books, the internet, your LFS staff or other hobbyists.

2. Have you exhausted your treatment options?

Few diseases are as straight forward as Dropsy and many can be easily cured with good water conditions and inexpensive over the counter aquarium fish medications. As a pet owner, it is your responsibility to treat your sick fish appropriately. Once you come up with a reasonable diagnosis, treatment is a two part process. First, discover and fix the cause. (Poor water quality is often the culprit) Secondly, treat the illness itself. (antibiotics, antiparasitics, temperature control, etc.) Treatments can take time and effort and let’s not forget that the fish’s own immune system will work to combat disease as well. Most common fish illnesses ARE curable.

3. Does your fish still have the will to live?

Ok, this can be a little tricky to determine. My personal recommendation, take it or leave it, is if the fish tries to allude capture he still has the will to live. If he tries to swim away when you go to net him, then he is still utilizing his fight / flight response. If the fish allows you to scoop him up, he may be too far gone to save. Still, this isn’t 100% confirmation that the fish should be euthanized. I personally have had a Betta splendens that was so sick you could scoop him up with your hand, but because I was too squeamish to euthanize him my only option was to treat for the illness and wait until he succumbed. Remarkably, the Betta recovered fully and lived another year and a half. On the other hand, there have been many that I have been unable to save. This is ultimately your judgment call. Consider the physical state of the fish, the suspected illness and the age of the fish. A two year old Betta may recover fine and live for another two years. A 5 year old Betta is already nearing the end of his natural lifecycle.

How to Humanely Euthanize a Fish:

There area several methods for aquarium fish euthanization frequently utilized by hobbyists but only a handful are considered humane. Unfortunately, some of the methods previously considered humane have decidedly been determined not to be so. Here are a few methods considered to be a safe and humane method for euthanizing fish.

1. MS 222 [Tricaine methanesulfonate]:
MS 222 is frequently used as anesthetic and a sedative for aquatic animals but in larger concentrations is the preferred method for euthanizing aquarium fish. It is approved by the FDA and considered humane by the American Veterinary Medical Association. It can be purchased through your vet or online. A bath with 250 mg of MS 222 per liter of water is adequate. The fish should be bathed for a full 10 minutes to assure death.

2. Benzocaine hydrochloride:
Benzocaine hydrochloride is similar to MS 222 and is a safe and humane method of fish euthanasia. A concentration of 250 mg per liter or more is effective for euthanasia. At this time I am uncertain of availability. Contact your Vet for more information.

3. Eugenol [Clove oil]:
Eugenol, the active ingredient in clove oil, is another sedative that when used in high doses is safe for fish euthanization. It is not approved by the American Veterinary Medical Association but is considered safe and humane by most aquarists. It can be purchased at your local pharmacy or in most health food stores. Being an oil, it does not dissolve in water. Once the oil is added to the water it must be shaken vigorously and the fish should be added immediately before the oil has the chance to separate. Doses greater than .25 ml per liter of water is adequate.

4. Decapitation:
While this can be the most difficult for the fish owner, it is considered humane and is the quickest euthanization method. Using a very sharp knife, detach the head from the spinal cord by cutting directly behind the gills. To avoid stress and discomfort associated with removal from the water, utilizing one of the above mentioned methods for anesthetization may be desirable.

Questionable Methods:

The use of Alka-Seltzer® tablets in water or high concentrations of Ethanol (AKA the Vodka Method) will cause death but it is not known to be free of pain and suffering. It is likely that these methods are humane when dosed properly. At least two tablets of Alka-Seltzer® per liter of water or 30 ml pure grain alcohol per liter of water are the appropriate doses. Because fish frequently react physically to these methods it is unknown what, if anything, they are feeling. Because of this, these methods are considered inferior to the approved methods above.

Unacceptable Methods for Fish Euthanization:

1. Freezer Method:
Dropping your fish into freezing ice water or putting them in the freezer to slowly freeze (hypothermia method) does not quietly put your fish to sleep. In cold blooded animals, it is believed that the formation of ice crystals in the tissue may create discomfort or severe pain. The hypothermia method is never ok. Rapid freezing may be applied only if the fish is deeply anesthetized prior.

2. Flushing:
Flushing your fish down the toilet is not only cruel and inhumane, but it is also illegal. Flushed fish can survive for hours or even days exposed to horrific conditions and toxic water quality. Flushing sick fish can also contaminate your local water shed with aquatic diseases. This method is never appropriate.

3. Boiling:
Dropping your fish into boiling water is painful and does not cause instantaneous death. This method is not approved.

4. Other Methods:
There are dozens of other methods for fish euthanasia circulating among the hobby that are not considered humane. The ethics of euthanasia in general are often debated. If you determine that euthanizing your aquarium fish is necessary, please only consider humane methods that remove all pain and suffering from the equasion.

American Veterinary Medical Association, “2000 Report of teh AVMA Panel on Euthanasia.”JAVMA. Vol 218, No. 5. 2001. http://www.avma.org/issues/animal_welfare/euthanasia.pdf

Dr. Harms, Craig. “Euthanasia in Fish.” PetPlace.com. publishing date unknown. 12 Feb 2007 .

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Christie F is a Betta splendens hobbyist that enjoys spending time caring for her fish and helping new betta keepers learn the ropes. More posts by:

9 Comments for this entry

  1. Anonymous says:

    I read on your site that older bettas get cataracts. My fish is going on five years old and just this past week has been having trouble getting his food. He darts at it but misses, like he either can’t see it good or can’t get to it . He is also swimming a little bit on his side and having trouble turning around in the tank. Can you give me suggestions on how to help him. His name is Ron Weasley. We love him very much and realize he is getting on i years but don’t want to lose him. thanks, donna

  2. Christie says:

    Donna,

    You must have done an incredible job to have a 5 year old Betta. Kudos to you. That’s about equal to 130 people years. Not too shabby! Sadly, as nature runs its course your betta will eventually succumb to old age. The loss of sight (looks like cataracts but we don’t really know) can make eating a little more difficult for your betta but he can still use his other senses to reach his food. You may notice him lunging more but as long as he doesn’t have to compete with other faster fish, he should still be able to eat. You can also ensure he’s getting enough by dangling the food in front of his mouth with a pair of aquarium forceps, tweezers, a pipette or a toothpick.

    Difficulty moving around and gradual sluggishness is also part of getting old for Bettas. For a fish as old as yours, there really isn’t a lot you can do to bring back his energy. I suggest keeping the water clean and warm around 78 F [26.6 C]. Cold blooded animals have more energy when they’re warm. Continue to feed him a nutritious diet and avoid stressors. Watching your aging Betta reach the end of his life can be sad but you can also find some solace in knowing your provided him with the best possible home you could and that YOUR betta is one of the few that get to live a long full life.

  3. girlfire23 says:

    My betta seems to be slowly seeping blood from the top of his head… he has not eaten in at least a week…he is constantly staying at the surface… has lost all of his personality and basically just sits at the top of his bowl motionless. I clean his tank at least once a week… and the water appears to be clean but it smells like he is exuding some kind of oder. Not sure what the right thing for me to do is. please help.

    C

  4. DFox says:

    Suggest you look at the American Fisheries Society Publication on this exact issue. I do not think the report you site is the most up to date.

    http://www.fisheries.org/afs/docs/policy_16.pdf

    • Christie F. says:

      Thanks for your resource DFox. I read it carefully and cross-referenced it with the FDA website and the original report I got my information from. For the most part they were in agreement. I should note that liquid nitrogen and electroshock aren’t really options for most betta fish hobbyists. Your report was in regards to fish research so of course, laboratories would have better resources than most of us.

      One mistake in the [Guidelines for the Use of Fishes in Research (2004)] said that MS-222 is not approved by the FDA. It actually is and has been since I believe the late 90s, though it is hard to pinpoint approval dates on the FDA website. Of course, for euthanasia purposes it is supposed to be prescribed by a licensed Vet. (Again, very few of our readers will ever consider this method).

      Thank you for sharing your resource with our readers and for prompting me look back and review my 2007 article. I definitely want to be sure the info I’m sharing is still valid and up to date. :) It looks like it is.

  5. Terry says:

    Christie,

    I believe my betta, Batman, is suffering from dropsy (raised scales, bloated stomach). It’s been just about two months since I first started noticing the bloated stomach. At first, I thought it was just an issue of overfeeding (I had family business to tend to so I left him with a coworker). However, after putting him on a diet for a few weeks and his stomach still not going down, I did more research and found out it was dropsy. I’ve tried treating him with epsom salt baths every couple of days the past couple of weeks with frequent water changes. When that didn’t work, I tried diagnosing him with API General Cure (supposed to help “swollen abdomen”). I’ve been treating him for about a week with the medicine now but still no improvement.

    I’ve had Batman for just over a year now, and every day I come home from work, he still swims up and greets me. He always has a good appetite in contrast to what people in other forums say the fish will be like when suffering from dropsy. The past couple of days, I have noticed that he seems just a tiny bit more tired than usual. And last night, I noticed that there are some white stuff starting to form on the tip of some fins. Do you think it is time to put him to sleep even though he is still so active? It hurts me so much to see the condition that he is in, but he is still swimming around like it’s okay. I’ve had Batman since he was still little, so I’ve developed a lot of feelings for him :(
    Your input will be greatly appreciated.

    Thanks,
    Terry

  6. Mare says:

    Thank you for this very valuable info. Our lovely sapphire male Betta, Gill aka Fin aka Blue Boy came to us almost 3 yrs ago now after being given to a friend whose mind, time and energy was/is occupied with her terminally cancer-stricken husband so this poor betta had been relegated to the inside of a china cabinet and largely ignored and rarely fed (outta sight/outta mind) as she’d been erroneously told he could eat the plant that was in the container and she didn’t know he was a carnivore! His container had been stuck inside the china cabinet so that her cats couldn’t get at him. As she hadn’t the time nor inclination to properly care for him and asked if we could take him we agreed and took him off her hands and have enjoyed him very much…’til recently when for the last 2 months, he suddenly stopped eating altogether and despite things we’ve tried to do to help him, he’s slowly but steadily gone downhill:-( The pet store people gave us different things to try but said he was probably just old and dying as we’d already had him almost 3 years, is that true? Anyhoo, this afternoon I found him lying on the bottom, still as death and barely breathing. I followed your suggestion to see if his fight/flight reflex was still there but sadly it was not. We haven’t the money to afford to take him to the vet to get the things you suggested and I couldn’t find clove oil at any pharmacy in our city. We couldn’t stand to watch him suffer this way any longer so 1/2 hr ago, my husband who is a fisherman, took his very sharp fillet knife and quickly dispatched poor Gill as your article instructed. I didn’t want to flush him as everyone was suggesting to me to do as I felt that would be cruel so I’m really glad now that I saw this article and learned that it really IS! I can’t help but cry as I type this message…I know my family and friends will say I am just being silly, they’ll say that he was ‘just a fish’ but we don’t feel that way at all! I can’t help but wonder if the ceramic log I bought him 6 mos ago might have slowly been leaching chemical toxins such as lead into his water as it was made in China and I’ve since then read some not very good things about Chinese glazes? I guess it’s pointless now to wonder as it’s too late for my wee guy…just wish I’d read that about suspect Chinese glazes before now as I wouldn’t have kept using it:-( He really liked sleeping in it though. We just buried him with a short ceremony underneath a plant in our garden so that now his little body may contribute to the cycle of life and perhaps help another living thing (a plant) to benefit from his death and our loss. Thank you for listening to my blubbering and I apologize.
    Peace,
    Mare
    Anyhoo, sorry for this sappy message but thanks again, your article was most helpful.

    • casey says:

      Great article. I have to agree with Mare, a few days ago I put an aquarium log in my betta’s tank. A day later, the water was cloudy and smelled terrible, like plastic. I flushed out all the water and got rid of all the plants and rocks (they were permanently ruined). The next day my fish was at the bottom of his tank hardly breathing. I am able to handle him with my hands, which was never the case before.

      My advice, don’t buy aquarium decorations/plants from CHINA!

      What is your advice? He is in a small bowl and I am trying to keep the water around 80 degrees, but how long should I treat him before I euthanize him? I have had other sick bettas too… fortunately I never had to euthanize them but I just has a bad feeling about this guy :(

  7. Aimee says:

    Please help! I can’t stand seeing my roommates betta fish suffer anymore! I have tried treatments and such, he has been sick for 2 wks now. He has clamped fins, staying at the top of tank on a plant I rested in half tank of water so that he can get air easily. He isn’t swimming right and is having trouble breathing. I did one and last treatment of meth blue dip for ten seconds, I noticed his breathing has calmed some but still having problems swimming and still staying on top of the plant for quick air. :( please help, I don’t know what to do and if he has a chance I surely don’t want to kill the poor lil dude. He is a trooper and can tell he is fighting.

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