It is funny, it deals with poop. I never grew out of thinking poop was funny. But yeah, big fish+big meals=big poops. Nothing like your turtle's, though. Quality food (not loaded with filler) also helps cut down on the crap.
It would be helpful if someone had a 7" bluegill and could post a pic of the doo-log. A couple would be better. One turd at light feedings, one with medium, and one with heavy. Then lay the poo on top of a dime and snap a pic for reference.
Also the type of food will determine girth. Feeding a frog to your fish will make a MOAB.