I have my Anostomus gracilis in a tank alone (20G). The fish is evil and eats the fins off of any fish kept with it; I could probably keep some small barb/danio-type fish with it but cichlids are a no-go and any catfish/pleco would be dead in a day, this fish has killed (by de-finning) 2 cories and a channel cat. When I set up the big tank next spring I'm tentatively planning to add a 55G planted refugium; I'll try keeping the gracilis in there but with my luck it will eat the plants faster than they can grow...damn fish. I love it.