I saw two sores on its belly but no other marks. It was full of eggs but nothing unusual could be found. This is the fourth one in the past month come up on the shore dead. All are catfish and all are adults. All of the other fish are feeding and seem healthy. Any ideas? I thought I would find a hook in it or something but no nothing.

Could be injuries from spawning....

That's my bet, they're spawning and beating each other up... Females and males both take a beating.