No more than 3 prawns in one sitting, feed every other day unless belly is still swollen. You will find your cat more active. You could also go with a one prawn a day deal too. I feed my catfish everyday, but a reduced amount. Good luck on getting them to eat once they are at 3' though. About once every 3-5 days is a good amount once they are adults. Their metabolisms slow the larger they get. They need to eat less and less often and will still gain weight and grow some. Make sure that you do not overfeed as it creats more problems than just sick fish. You can also overload your filtration with a growing RTC. What size tank and what's the filtration?