Cory cats nipping Betta fins...?

Hi, I just started this new tank after many years of not having one.
I have a 20 gallon with a male Betta, 2 cories, and a young pleco. I had 1 cherry barb for a few days but he was nipping a my Betta.
I noticed damage done to his fins so I took him out. Since then, my Bettas fins have started to turn dark and ragged looking and his body has dark blotches as well. I figured he has fun rot so started his treatment today and I just noticed my Cory’s swimming up to the top of the tank and nipping at him! My poor Betta has had so much abuse lately!
Ive attached a picture of him as well.
Does anyone know why this is happening? Maybe they aren’t getting enough food?
If so, what’s the best to feed them? Pleco tablets, tropical fish food, or bloodworms?
I now have my Betta in a separate tank. Please can someone help out?

Sisu said:

Hi, I just started this new tank after many years of not having one.
I have a 20 gallon with a male Betta, 2 cories, and a young pleco. I had 1 cherry barb for a few days but he was nipping a my Betta.
I noticed damage done to his fins so I took him out. Since then, my Bettas fins have started to turn dark and ragged looking and his body has dark blotches as well. I figured he has fun rot so started his treatment today and I just noticed my Cory’s swimming up to the top of the tank and nipping at him! My poor Betta has had so much abuse lately!
Ive attached a picture of him as well.
Does anyone know why this is happening? Maybe they aren’t getting enough food?
If so, what’s the best to feed them? Pleco tablets, tropical fish food, or bloodworms?
I now have my Betta in a separate tank. Please can someone help out?

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Hello and welcome to the forum. I am sorry to hear you are having difficulties with your fish. From my own knowledge I am sure dories are best kept in groups of 4+ if your tank is big enough I would recommend adding more. Do you keep live plants in your tank? Your Cory fish will do better with shelter. You could try re-arrange your tank and see if that helps things settle a bit. If it continues I would advice removing your Betta or the Cory fish and placing them into a different tank to avoid stress. You mentioned that your tank is newly set up. Please ensure to test the water everyday for ammonia or nitrites. Perform a water change every time readings show above 0 for both of these as this could stress the fish out too. Ammonia is also toxic to all fishes. Weekly water changes during cycling are important too. A gravel vac can help assist you with this. I would recommend changing 50-75% weekly. Best of luck.

In addition to post #2, there are some issues to keep in mind.

First thing, male Bettas are not commujnity fish. A male Betta should be on his own in his own tank. Keeping it with other fish, especially upper level (tetras, barbs, and such) is only asking for trouble either from the Betta or from the other fish to the poor Betta.

Having said that, it is unlikely the cories are nipping fins of any fish, as they have no teeth. They will "mouth" one another and often other fish too, but I have never hear of this causing fin damage.

Back to the cory numbers, yes, they must have a group of at least five. A 20g tank is not much space, but five or six cories will be OK and they will bee stressed with just two or fewer than five.

Barbs, tetras, rasbora and danios are also what we term "shoaling" species, meaning they live in very large groups and the need for a group of their species is programmed into their DNA. So in future, do not acquire one, two, three, etc of any of these, only groups of at least six, but only if you have the tank space. A group of six or seven cherry barbs could manage in a 20g, with the group of cories, but certainly not with a male Betta.

Guppylover3x said:

Hello and welcome to the forum. I am sorry to hear you are having difficulties with your fish. From my own knowledge I am sure dories are best kept in groups of 4+ if your tank is big enough I would recommend adding more. Do you keep live plants in your tank? Your Cory fish will do better with shelter. You could try re-arrange your tank and see if that helps things settle a bit. If it continues I would advice removing your Betta or the Cory fish and placing them into a different tank to avoid stress. You mentioned that your tank is newly set up. Please ensure to test the water everyday for ammonia or nitrites. Perform a water change every time readings show above 0 for both of these as this could stress the fish out too. Ammonia is also toxic to all fishes. Weekly water changes during cycling are important too. A gravel vac can help assist you with this. I would recommend changing 50-75% weekly. Best of luck.

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Thank you for the quick reply.
My Betta ended up passing away
But I have more cories in the tank now. 4 total. Will stay away from having a Betta in a community tank. I’ve had luck with it before.
I know about water changes and I have a gravel vac. Thanks for the other info.

Byron said:

In addition to post #2, there are some issues to keep in mind.

First thing, male Bettas are not commujnity fish. A male Betta should be on his own in his own tank. Keeping it with other fish, especially upper level (tetras, barbs, and such) is only asking for trouble either from the Betta or from the other fish to the poor Betta.

Having said that, it is unlikely the cories are nipping fins of any fish, as they have no teeth. They will "mouth" one another and often other fish too, but I have never hear of this causing fin damage.

Back to the cory numbers, yes, they must have a group of at least five. A 20g tank is not much space, but five or six cories will be OK and they will bee stressed with just two or fewer than five.

Barbs, tetras, rasbora and danios are also what we term "shoaling" species, meaning they live in very large groups and the need for a group of their species is programmed into their DNA. So in future, do not acquire one, two, three, etc of any of these, only groups of at least six, but only if you have the tank space. A group of six or seven cherry barbs could manage in a 20g, with the group of cories, but certainly not with a male Betta.

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Well from your information...it just goes to show how little ppl at the pet stores know.
I’ve read info online about male Bettas being ok with certain fish. And a bunch of years ago I had one co existing with multiple fish.
The barb is what did the damage not the Cories. And then it got significantly worse in a few days.
But I did notice one of the cories swimming up to the top of the tank where Finn (Betta) was and did something that looked like nipping.
I moved Finn to another tank so he could relax and recover but he passed away soon after.
I now have 4 cories together and they seem to be doing well. Will make sure to do my research before getting any other fish.
Thank you.

Sisu said:

Thank you for the quick reply.
My Betta ended up passing away
But I have more cories in the tank now. 4 total. Will stay away from having a Betta in a community tank. I’ve had luck with it before.
I know about water changes and I have a gravel vac. Thanks for the other info.

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I’m sorry to hear

Sisu said:

Well from your information...it just goes to show how little ppl at the pet stores know.

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Very true. You will see many times on this forum advice from many members not to rely on advice from staff in most fish stores. Research is prevention, which is always better than a cure after trouble.

Sisu said:

I’ve read info online about male Bettas being ok with certain fish. And a bunch of years ago I had one co existing with multiple fish.
The barb is what did the damage not the Cories. And then it got significantly worse in a few days.
But I did notice one of the cories swimming up to the top of the tank where Finn (Betta) was and did something that looked like nipping.
I moved Finn to another tank so he could relax and recover but he passed away soon after.

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The barb naturally went after the Betta because the barb is a shoaling species and it must have a group, and scientific studies have now proven what many of us long believed, that keeping shoaling fish in too small a group will increase aggression; aggressive fish become more so, and peaceful fish become somewhat aggressive. This is because the fish "expects" to be in a group of its own, and when not so accommodated it is under severe stress and frustration. We cannot go contrary to nature, it just does not work.

The Betta was severely stressed by what he was forced to endure, not being alone, and internal issues resulting from the stress, weakened immune system, weakened physiology is not reversible. Some people claim to have had success with a Betta in with other fish, but this is not normal, and risking fish just to hope the abnormal will prevail is not wise. Research involves understanding what is normal behaviour for a fish, and then assume your fish will expect that. And, other members here could tell you of a Betta that they thought was "OK" with other fihs, only to have it turn and attack them literally overnight. Again, we cannot go against nature.

I explained the normal cory "friendly" behaviour; one author likened this mount/barbel interaction with other fish to be like a hug or a kiss. Comical, but perceptive in understanding the fish's behaviours. And that brings me to your last point:

Sisu said:

I now have 4 cories together and they seem to be doing well. Will make sure to do my research before getting any other fish.

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Cories are highly social; they live in groups of hundreds. Studies have shown five or six is minimum for the fish to (hopefully) be OK. A couple more will benefit your four, believe me.

Hi guys i have a betta and a Cory and 4 guppy fish. Now i don't know who is nipping the fins of my betta

Helllboy said:

Hi guys i have a betta and a Cory and 4 guppy fish. Now i don't know who is nipping the fins of my betta

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Most likely nipping his own fins due to stress

Betta males should not share their territory with anyone...especially flowy finned male Guppies since to a Betta male they look like another Betta male intruder in their territory and when that intruder refuses to leave, the Betta will take out its frustration on itself.

Helllboy said:

Hi guys i have a betta and a Cory and 4 guppy fish. Now i don't know who is nipping the fins of my betta

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Probably no one but probably degeneration of the fins itself (finrot).