Are cories aggressive?

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sdb

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May 4, 2004
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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. :confused:
 
I've never heard of cories being aggressive at all--maybe a bit pushy about food, but not aggressive. I've had to remove cories from a tank because they were pushed around or nipped at by more aggressive fish--and I've never seen any sign of aggression from any of mine.
 
Thanks, OG. That's exactly how I feel. I've done a lot of reading about cories because I like them so much, and never once have I read anything about them being aggressive. They're totally opposite as far as I'm concerned. And I agree about them being a little pushy at mealtime, it can be funny to watch them push each other around in that cute little way of theirs.
But aggression, no.

I'm pretty choked at my LFS, and it's the only one in town that I ever bought from. The only other one has too many dead fish.
I'm seriously considering going out of town to get my fish when my 33gal finishes cycling.
 
Cories are the least agressive fish I know. they just spent all day forraging and playing. They're a little cheeky when it comes to food pellets but nothing bad. I reckon your LFS is trying to cover their backs with a little 'creative information'.
 
I would think that the problem was with the betta and not the cories. I have 8 peppered cories in my tank and they generally seem to ignore everyone else even durring feeding time. Every now and then one of my german rams will push some cories away from some food, but I have never seen the cories try and outmuscle the rams.

One thing you don't say is how you introduced the new betta into your tank. It is possible he just didn't survive the transistion from one tank to another.
 
I floated the bag for a while, then sucked out about half the water with a turkey baster. I then replaced that water with about the same amount of tank water. After a while, I gently netted him out and into the tank. It's how I've always transferred new fish, and I've yet to lose one yet. I also didn't feed him or turn on the lights at all, to try to keep things calm for him until he felt a little more comfortable.
I agree the LFS is trying to get out of being responsible. The only thing they've accomplished is by losing a customer, which is a big deal in a small town. Replacing the fish would have been way cheaper.
I'm glad everyone confirmed my belief of the cories being gentle. Thanks for all the replies (and the link, swimfins).
 
Yeah, it sounds like your method of acclimation should have been sufficient. I still get shocked when I hear about a LFS that refusses to replace a dead fish after such a short amount of time. Out of curiousity how often do you test your water parameters?
 
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