TDK +1 on what Fish said. RES are a great maintenance fish for sure and they don't normally cross breed with BG. Oh maybe from time to time but unless I'm mistaken RES only breed like once a year and BG can breed 5 or 6 times a year... but if they did x breed I don't think it would be smaller that's for sure! Considering RES can grow up to 3 to 4 pounds...
RC