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If your betta is old, sick and suffering, you may not want to sit and watch him slowly wither away. He may not want to wither away, no one knows. You may have a large spawn of babies, too many. You may need to thin them down. These are not things we do to be monsters, they are things that we feel are necessary. If you don't agree, then you don't need to read any farther.
Before I get into the various methods, I will take a moment to offer alternate suggestions for culling. One thing about culling, is that you can never tell a fish's true colors until they are grown, so keep this in mind. Also, many pet stores will trade supplies or live food in exchange for fish. Sometimes they will even buy them. There are also always fish/betta lovers willing and more than happy to make a home for culls. These are the alternatives to culling your spawn. 

Please note that when I talk about 'culls' here on this page, I am not referring to the overly deformed or ill culls that I do not believe should be forced to live in those conditions. I also do not believe they should be sold (as I have seen done) or given as 'gifts' (which, again, I have also seen done). If you wish to keep these deformed bettas alive, to fight to swim for air, to struggle to get to their food, then do so. I ask that you not try to pass them off as gifts to unsuspecting customers. Most customers are willing to adopt a cull, but I don't think many expect to receive a fish that can barely swim. Ok, back off my soapbox :)


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Culling your Spawns

bulletMany people do not have thee space in their homes to house hundreds of young bettas. This does not mean that they should not take up another hobby, by any means. For this reason, many breeders might need to cull their spawns fairly early on. If you are one that needs to do this, please remember that sudden cases of velvet or other illnesses can wipe out the majority of a spawn, so think carefully when choosing to cull your spawn early.
bulletYour first option is to only start with a small spawn. You can do this by removing the female during spawning. Watch her and count the eggs she releases. When enough eggs have been released to satisfy what you feel you can handle, remove her from the spawning tank. She will most likely release the rest of her eggs in her own bowl and make a snack of them. This is one way of keeping your spawn small and not having to cull later.
bulletOne was to cull your spawn early in their lives, is to use a small siphon and suck them out of the tank and into a cup of ice water. I have never done this (I happen to HAVE plenty of room for all my fish, lol) so I do not know about it first hand but have heard it kills them instantly.
bulletIf you are breeding for certain color or fins and want to cull out the unwanted, less than the best juveniles (after, of course, checking with local fish stores to see if they would like to trade for supplies) then you can take the remaining ones that you no longer wish to keep and feed them to the Oscars at your Pet Store. You may be shocked at this concept, but I find it one of the best methods. Not only does it rid you of the unwanted fish, it also serves a purpose for the Oscars so your fish's life does not go in vain.

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Euthanizing your Adults

bulletFreezing: I know of many, many people who use this method, but I really don't know for sure. I doubt any of them have sat in the freezer and watched to see if their fish suffered or not. I have recently read that a breeder placed some bettas out in sub-zero weather (as cold or colder than a freezer) and watch to see if they suffered. She reported that they thrashed around and did not die for over a half hour :( I also did a test of my own. I froze a diseased betta that I had to let go. After ensuring he was frozen solid in the freezer, this was after hours in there. I placed his frozen body into a fish bowl of normal water. Within an hour, he thawed and was attempting to swim around. I have never used the freezing method since...horrible :(
bulletCold Water: It is suggested to take a small container, such as a betta hex, and fill it with cold water and add a couple ice cubes. Once the ice cubes are half melted, move them aside and place the betta(s) to be euthanized one at a time in the water. There seemed to be no thrashing or apparent suffering, they simply 'fell asleep'. Now, this method does not kill the betta, only puts it into a state of unconsciousness. I really can't recommend this method either.
bulletAnesthetic overdose: Use 3-4 times the recommended dosage of any of the commonly used anesthesia agents. Because of the risk of recovery the fish should be left in the solution for several hours.

One formula that is very well known is Clove Oil & Vodka. The only reason for the vodka is to help the clove Oil dissolve into the water. Do NOT increase the Vodka in hopes it will help your fish die faster, it will cause more discomfort. Increase the Clove Oil, if anything. Clove Oil is used by veterinarians as an anesthetic to put fish to sleep. Use this and your fish will do just that, fall asleep. Here is the recipe:

First, mix 2 ml clove oil (can be obtained from a pharmacy or health food store) with 8 mls vodka to make a 10 ml stock solution.  Place the fish in a container with one gallon of water and add the 10 mls of clove oil and vodka to the one gallon of water, and the fish should just go to sleep quietly with no struggle. Clove oil (eugenol) is used as an anesthetic in fish for surgery, and the vodka is necessary so that the clove oil will dissolve in the water.  If your fish struggles, it is most likely because the vodka level was too high. Never raise the vodka level, please. The vodka may come in handy afterwards to wash down the guilt :(((

You could also use a fish anesthetic called Finquel MS-222. An overdose will peacefully euthanize a fish. You can purchase a small bottle of the stuff for under $10 from Argent Chemicals. Their website is

I have never used this method so I do not know how efficiently this works.

bulletDecapitation: This is only suitable for smaller fish. It is assumed to cause instant unconsciousness. Remove your fish, place them in a paper towel or something so you have a good hold on them, place a very ,very sharp knife right behind the gills and slice with one, quick motion. Be prepared to cry, some of that vodka might come in handy again :'(

           I have never used this method so I do not know how efficiently this works.

bulletCranial concussion: A sharp, single blow to the head with enough force to damage the central nervous system. This may kill small fish outright, but larger fish may only be stunned. Place your fish in a fish bag, I would not stick but a teaspoon of water in it, then snap it on a table's edge. Just thinking of these makes me want some vodka *sniff sniff* Anyone who has to do these, I really feel for you.
bulletSodium bicarbonate (baking powder or Alka Seltzer): This is not an accepted form of euthanasia and will cause a degree of discomfort and stress, but it is readily available and can be used in the home if there are no other alternatives available. Decapitation may be required once the fish has lost consciousness to ensure death and that the fish will not 'wake up' in the garbage or septic tank. I can't imagine even trying this method, but wanted to mention here mainly to warn you against it.

           I have never used this method so I do not know how efficiently this works.

bulletPoisoning: There are many chemicals that will effectively kill fish. None are considered humane and will all cause considerable distress unless the fish is euthanised first
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  March 23, 2009 10:27 PM CST Pet Sites

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