Lets say your inventory is full and you catch a mythical fish with its tag and there's tons of people around you. One person picks it up but doesn't give it back to you and claims it for themselves. I think there should be a system where if your inventory is full it goes into a place where you can claim the fish head and the tag later.
I don't believe that the fishing plugin is custom, so I'm not sure how possible that would be. Definitely an interesting thought, but I think that it's better to just report them to staff, as they can get it back for you for now
I have been told you fish in 1 spot, you will stop getting fish but you will get the secondary drop like dragon fish bones and suffix