One word of caution about offal...if it isn't eaten by something, you end up with some else for the water to decompose. Plus, if you toss heads, fins, vertebrae...one of the worst "fish" related injuries I'll always remember was stepping on a fish fin (without a fish attached) that went through my deck shoe and about an inch into my foot. Couldn't walk for five days, had to get a tetanus shot and the doctor had to lance it three days into the ordeal. I'd had a fish kill and didn't remove all the dead fish and two years later, paid for it. I no longer put offals into any of my ponds.

Teach a man to grow fish...
He can teach to catch fish...