Geez...and I only thought channel cat were the stepchildren of southern fishing ponds, periodically donating their omnivorous bodies only to palates of science. Theo Gallus, fisheries philosopher and seer of bigger things has brought new information to the table. Well done. It has never entered my mind to measure the mouths of channel cat.
Theo, would you like to write a story for PB? If so, let's do it. I'll help. Heck, if you hurry up, we'll put it in the Sept-October issue.
You are right on the money deducing the larger mouths belong to males. But, it's because females are larger of the species. They tend to be longer and heavier, while males of similar length are lighter weight, with wider, more flattened heads. Depending when you measure, females are much heavier, especially when their ovaries are full and the males have one thing on their minds.
Another twist to your theory, though. Think about this. Even though a given size shiner will fit into a given channel cat mouth, that doesn't mean channel cat will be effective predators. One of the most fun things about fisheries management is to take solid science such as Theo and Cody's stuff, then put it to work in a pond. I love to eat oranges, but I ain't drivin' to Florida to get an orange. Golden shiners are fast, and quick. They live in open water, near shore, normally in the top few feet. Channel cat are typically skittish, nocturnal, hanging deep as they can. I love Theo's fact finding. Let's take it to the next step and answer the follow up question. Will channel catfish effectively prey on golden shiners in Theo's pond, based on mouth size of catfish and length of shiners? When we take solid scientific evidence and mix it with a behavioral study, now we have the makings of a great story.
Theo, why don't we write a story based on your current findings, with a hypothesis, then a follow up on the behavioral aspects?

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