Biggish fish able to hold its own in 20g with gardneri killifish


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Just looking for some ideas out of curiosity (if nothing comes of this I’ll just separate the fish which isn’t a big issue either) for a fish that’s at least 3-4 inches long or bigger for a 20gal. It’s kept at 76°F. I have a male and female killifish pair with a male and female peacock gudgeon. Today (see my posts) I discovered after putting all my fish in the same tank (which I’d planned to do all along but had to wait for the gudgeons) I realized 2 things.

1. My fish are really stupid. The female killifish was acting territorial and puffing her gills/fins out in a big display at every fish in the tank, including the male killi whos bred with her before. Likewise, the male gudgeon was determined to duke it out with her by circling her constantly with fins all flared and chin puffed out. They all think they’re the same species, apparently, and are very confused. The only non aggressive fish was the female gudgeon watching it go down, and the killies kept attacking and chasing her between displays for no reason. They’re bullies without a cause.

2. No fish I have can put the male killifish in his place. I don’t know if a more intimidating fish to him would make a difference in his behaviour and bring peace to the tank, but there needs to be some balance because he’s been a terror to all the fish in my tank since the moment I’ve had him. I have to keep him alone in the spare tank because he relentlessly chases and shreds the fins of any fish he rooms with, save breeding, and is the largest fish I own. He’s a bully that has nothing to challenge him.

I don’t want to endanger any of my fish but I’m wondering if there’s something akin to a peacekeeper for fish, one that could somehow reduce this aggressive behaviour or at least balance it out and bring peace to the tank. The only fish I have that he hasn’t attacked have been 5 cardinal tetras, which were in the tank before he was and not for very long, and the otto, which hides. Any ideas?


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More than 10 years
Giving this a bump up for you hope you get some suggestions today

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