Catching and killing the How to Fish Tuna can be tricky as, despite only being a miniboss, it's a particularly furious fish. The Tuna is massive, can bounce and leap very high, and hits like a truck, so you need to take care when fighting one, especially since the lure required to catch it is rather expensive too, so you don't want to waste them. But you need to kill a Tuna every time you want to fight the final boss of island 4, so it's good to know the best way to defeat one in How to Fish, which I've laid out below.
How to catch and kill a Tuna in How to Fish
Like the How to Fish Shark, the Tuna seems to be a guaranteed catch from the Professional Boss Lure, which you can buy from the shop on island 4 for $1,200.
But be warned that the Tuna is a pretty tough fish and I recommend packing an upgraded SMG (if you've still got your old one from island 3, swap the compensator for a suppressor and get all the bullet upgrades) and a sniper rifle with a suppressor, extended magazine, and all the bullet upgrades you can afford. I personally preferred the SMG as it was much easier to spray bullets at the Tuna rather than be precise with the sniper rifle, but both are good to have.
When it comes to fighting the Tuna, there's nothing particularly special about the fight to be aware of other than that it can leap very high and almost attack from above. Again, it's like the Blue Shark in that it's just a very big and very aggressive fish that flops about and pounces towards you to try and bite. Strafe to avoid its lunges, and shoot it as much as possible when it repositions to have another go.
The only other thing to bear in mind is that island 4 doesn't have much to disrupt the path of the Tuna, unlike the trees on island 3, so it can move a bit more unpredictably. You can try luring it into a building in the hopes that it will get stuck, but you also put yourself at risk of getting battered in the tiny rooms. Although, I recommend having some clams or spare fish on you to eat and heal if the Tuna does indeed strike you.
Once you've killed the Tuna, you can cook and sell it, which should bag you roughly $4,000 – more than enough to make up for the expensive Professional Boss Lure. But you also need one to summon the final boss of island 4, the Albatross. To do this, you just need to drop the Tuna's corpse on the central grass patch, and the Albatross will eventually swoop in and destroy it, so you won't be able to sell it afterwards.
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