Like he said, all of the fishing functionality is being checked by the server (except for your own durability which is purely clientsided).
fishing strength (your "damage" to the fish per tick) is being checked. and the interval per tick is also being checked.
so you can't force it to "tick faster" and you can't force it to reduce the fish's durability ("health") in bigger numbers.
there's really nothing you can abuse in fishing except for your own durability and botting.
It's funny though, tons of other
very important game features aren't being checked and can be freely abused (like that revival item, which to me seems like a game breaking flaw).
but fishing? no. let's put all of our strength into making it fully serversided and secured. hehe go figure..
