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.