Originally Posted by lamberb2
You could possibly do a black ghost knife fish, in aquariums there rarely reported over 12 inches long, There are a couple different catfish you could look into also.
I must disagree with this. The BGK will easily attain 20 inches if it is healthy. And having an inflexible body it needs a tank at least 2 feet in width so it can turn around, and the length should be no less than 5 feet, preferably 6 feet. It has some other specific needs (dim light, lots of cover, hiding spots) and is basically a nocturnal fish. In the normal tropical aquarium with lighting this fish will be severely stressed. I would not recommend this species of fish to aquarists recently new to the hobby.
To the OP (mickeymcmick), welcome to Tropical Fish Keeping forum, and to this wonderful hobby.
To your original question, I would refer you to our profiles, second tab from the left in the blue bar across the top of the page. There are many species included, with data on numbers (some fish need a group, others are fine alone), minimum tank size, water parameters, etc.
Fish are living creatures, and each of us has the responsibility to ascertain the particular needs of a fish before acquiring it. We all learn the longer we are in this hobby, but we aim to know enough before acquiring the fish that we can prevent undue suffering which can otherwise easily occur.