Recently I've fished Rocky Point with my boat for a few days I've crossed back several times into the States with a lot of cleaned fish and they don't care at all. I've asked them if there's a limit, and they said there really isn't, as long as you're not bringing it back for commercial purposes (like if you're coming back with a few hundred pounds). So as long as you're using it for personal purposes I don't think there really is any limit. Main point is just declare it, be honest, you'll never get in trouble that way.
Thanks I thought I remembered something about 50lbs, but I dont think they will bust out the scale.
They don't. Make a point of declaring it, though. I usually say "some sport caught fish and shrimp I bought at the market" At most, they might open the cooler and take a peek, but that's about it. Unless of course, you've got a dozen coolers all full! Never ever been an issue for me, even with two large marine coolers full of fillets.