Answer:
Nothing! An adult blue catfish is at the top of the food chain. They are only sustainable in major rivers and largereservoirs fed by these rivers. The blue catfish requires a large forage base only available in these environments. So you won't find any blues in your local farm pond. I'm sure larger fish feed on adolescent blues, but adult blues have no natural predators. It is not unusual for an adult blue catfish to reach twenty pounds or more in a short period of time. I have recently become addicted to catching these fish, and have used several different methods. So far, my biggest is a thirty pound monster, but I'm looking to go bigger. I practice catch and release for any blue larger than ten pounds, as these are breeding size fish. I have some pictures and techniques posted at the following link. Good luck!
http:/hubpageszperiodzcom/hub/catfishhunter