No, you don't have to kill one.
It's only in extreme cases of deformity in the fry when you might have to make the decision to cull a betta.
I've never had to deal with such situation as I've never had a deformed fish in a spawn but I was faced with an emergency early in my betta keeping where one of my fish jumped out of his tank while I was at work. I found him on the floor covered in dust and very close to death.
I used the freezer method because I didnt want him to keep sufering, he had had enough and was going to suffer much more if I had placed him in water and try to bring him back to life. He was not going to make it.
When you breed/spawn or keep fish-you often are faced with a hard choice..."Humane euthanasia or allowing the creature to suffer needlessly"
Humane euthanasia should be fast and the fastest method is often the hardest method for some....but you need to view it as-"what is in the best interest of the creature"...not you......killing something is never going to be easy for most of us.....so when the deed needs to be done.....do it fast......decapitation and smash the head/brain.....faster the better.....small fish it can be harder but can still be done by using newspaper and placing the fish between it-use a heavy book or a hammer...don't hesitate....make a hard clean hit-roll up the paper and dispose of properly either in the trash, burn or bury.....
While clove oil is highly recommended- I personally find it too slow and the fish appears to suffer in the struggle too long for my taste...slow suffocation IMO seem cruel....
If I couldn't destroy the head/brain I would freeze-when done properly it is fast, painless and limits undue suffering-depending on the fish current state-I would start with very cold water (under 40F) to shock them first so that the system would shut down quickly-it is then a matter of time before they stop breathing while in the unconscious state while in the freezer and by using a small solid disposable type container with a top of some type can help limit your viewing (like a tin can, styerfoam cup).
Never flush a live or dead fish down the toilet-this is not only cruel for a living fish/aquatic life- but can have a negative impact on our environment....
If I was culling due to deformity and not health per se...I would gut load them and feed to another fish.....never feed a sick fish to other fish...
Culling is never going to be easy-but sometimes we have to...its a selfless act on our part and its our responsibility as responsible fish keepers. If you can't bring yourself to cull-then you should not breed fish because culling is a realistic part of breeding.......
Well said OFL. I was actually waiting for your response here. Thank you.
About the freezing, I was thinking the same thing, but was told that freezing is making them suffer and is cruel. I was thinking to get a very small amount of water, then make sure it is as cold as possible and shock the fish while everything is slowing down. (I have shocked a fish for the first time a while back [by accident] and it was really hard to get him back to his healthy self.) Then stick it in the freezer.
Maybe a half pint cup will help this process go faster?
OFL, I kind of know what euthanasia is, but am a little foggy on it. Is it always (opening the body of an animal?)
I havent had to cull a betta yet (I havent had a successful breeding pair yet) but I have culled guppy fry before, and I find that the quickest way to kill them is to just stab them thru the head, I know it sounds horrible, but it ends really quick.
either that or you can feed them to any bigger fish if you have some, when my guppy fry die now, I feed them to the severum upstairs :P
Well I have never had to cull a fish at all! I know sometime in a couple generations, I will have to eventually do it.
I might just stick to the freezing and stuff after OFL answers my questions. Also if times get rough I will attempt the decapitation or the book thing. Talking about this sends shivers down my back, but I know that is has to be done.
Euthanasia is just the term used for "putting them to sleep"
You may be thinking of the word- "necropsy" which is when you cut them open-like an autopsy
Also, FYI-even with the decapitation to sever the spine and destroy the brain-the heart may still beat for up to 15 min....usually it is less- but without the head they don't feel anything...remembering that the fish perception of pain is different than it is for us.....