Predatory cat

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Asian red tail is different to nemurus, nemurus max out at 12inch and are also less aggressive artc will kill anything it's with....
 
I'd go with a catfish that does not exceed 1' TL and stands its own. Even so, commming aggressive fish is always a gamble, an experiment that may or may not blow up in one's face.

Sun catfish, 4-lime pim were good suggestions. Both of these would do better in a good group of say ~6. A more exotic and rare loner would be a bolt catfish - http://www.planetcatfish.com/common/species.php?species_id=725

Hemibagrus nemurus, Synodontis eupterus or other larger, riverine, territorial synos may be considered. PCF Cat-eLog can be filtered by size, btw.

The problem with wood catfish is they are maniacally nocturnal.
 
Sun catfish is probably your best Bett for a predator, 4-line pims are aggressive to one another so you will need a group which I think will turn out to be to much once full grown for a 180, they are also not the most predatory cats but will snack on meaty foods if it fits in their small mouth. I will say they can handle their own with SA fish, I had two that did very well with a large jag, midevil, butti, an exceptionally aggressive Oscar, and a wolf who occasionally took chunks out of them but they'd heal fast. They'd fight back till the other fish got tired if need be, needless to say they are great fish, and I am thinking of starting a smaller set up to grow some out with some other fish I have. I also had a big leporinus take a small chunk out of one of them. They fought too. It was an aggressive set up, everyone was 8"+ the smaller pim being the smallest fish at 8 inches. The rest were more around a foot. Also if there's a significant size difference between two specimens expect one to get beat up time to time by the larger one to keep the smaller one in check.
 
Is the requirement on it eating other fish firm? Cuz if you want something with a predator attitude and can keep a good while with your footprint is a vulture catfish. Look them up, from experience I can say they rock and can be real lookers. If it is firm, my buddy really liked his gulper catfish but i dont know anything about them.
 
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