I have been using live buegils for cats for over 20 years I have caught them all blues, flats and a lot of channels on them. I mainly fish for flats but all the cats like a live bluegil. I see where some one said they use green sunfish, I believe what they are talking about is what we call rockbass here in st louis , I believe the official name is warmouth bass. These are tough little mean guys and work better than a bluegil but they are not as easy to catch. I always use as big as the rockbass are the gils as I can catch. It dosn/t take much of a cat to eat a large bluegil, hand size is great. Where i fish on the mississippi there is a lot of current, so if you hook them in the back they get turned around and it blows out their gils and kills them. I always hook them it the mouth , in the hard cartrage area. Another thing I always do is slit their stomachs to get the blood smell in the water, they will stay alive for a long time like that and you will catch more.