I've seen a couple threads regarding tackle boxes, which I feel is a pretty good idea, but I can generally keep my tackle under control (roughly half a page of inventory space).

Where I get bogged down is the actual fish I've caught taking up a page/page and a half of inventory. So my idea is similar to the tackle box idea, but a creel bag instead. It could be equipped as the secondary weapon, perhaps manufactured by a weaver or leather worker, with a set number of slots for fish, perhaps increasing as the level or quality of the bag increases.

Just a thought, but I'm sick of all the limsan anchovies and gobies in my inventory bag...starting to smell...