Fu Manchu lions don't need alot of room to swim since they are not very active spending most of there just sitting on a rock or sand or in a cave doing nothing I also believe they are the smallest lion to but apparently it's hard to get them eating in a aquarium another cool predator would be a leopard toby puffer but the tank might be a tiny bit to small for one of those but I have seen them done in 10 gallons before and doing ok
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