It could be that the insane nature of the cories stressed out your betta, I tried putting 4 female betta's in with my 5 hyperactive albino cories and they hated it, had to take them out pretty quickly. Cories didnt even notice them but would end up bumping into them all the time which was obviously stressing/****ting the betta's pretty badly, two ended up with fungus within a day and one of them died overnight.. only one still surviving, but she's a big tough fish now!sdb said:I had four peppered cories in my 10gal with a male betta. They were a blast to watch. The betta always stole the cories pellets and carted them off in his mouth. There was no troubles, aggression, or behaviour problems at all. Unfortunately, my betta died recently. I think from old age as he wasn't sick, the cories are fine, and there wasn't a mark on him.
Anyway, yesterday I bought another betta. He was swimming in a large tank with some bottom feeders and a couple fish. I put him in my tank, and he spent all day and evening hanging about the heater at the very top of the tank. No swimming at all, though his fins were always about half flared. He didn't seem concerned, he just didn't swim anywhere. The cories seemed to totally ignore him. I kept the light off, fed the cories but not the betta. Thought I'd leave it a day.
This morning I woke and the betta was dead. I called my LFS where I got him, and they said he was fine when he left, the other fish are fine, and that cories are aggressive about their territory. They figure the cories went after the betta during the night, ultimately killing him. I don't believe it, since the cories seem so peaceful and I've never seen aggression from them before.
Are cories aggressive (when I'm not looking!)?
Would they have ganged up on the betta and killed him?
It just doesn't seem possible.
Anyway, your cories might not be as abnoxious and inconsiderate (but still so cute!) as mine, so who knows!?
Hope I helped a little,
Ellen.
