Aside from helping to run a sushi restaurant and diving for artifacts, you'll need to catch a bunch of fish in Dave the Diver, too. As you progress through the story, you'll need to collect Cuttlefish skin fragments. For those not in the know, Cuttlefish look like little squids and spray ink at you when injured, so don't go looking for a traditional fishy boi.
You'll need a few weapon types to be able to catch one and will have to spend a bit of time hunting them in the hope some skin fragments drop. With that in mind, here's where to find and catch Cuttlefish.
Where to find and catch Cuttlefish
Cuttlefish are usually found around 50-70m down, where you start coming across oxygen canisters and more ammo. They often travel in a little group called a congealment, which is kind of disgusting but whatever. Finding them isn't really the issue here; it's more about how to catch them. They don't take a lot of effort to subdue, but you do want to try and keep them at a two or three-star rating, so using a tranquilizer gun is the best bet, as well as using the net gun should you find it.
Unfortunately, finding these weapons involves a little RNG until you gather enough resources to craft them, and then there's the issue of the Cuttlefish not always reliably dropping skin fragments. The less damage you do to fish in Dave the Diver, the better star rating they'll have, and higher star tier fish tend to be more likely to drop skin fragments. Once you've downed a Cuttlefish—you'll know because the fish will be floating and have that little shimmery effect—or caught one using your harpoon, you'll get a notification on the left if you've looted skin fragments. If they don't appear, try again, but watch out for the ink attacks.
If you can swim over to a Cuttlefish fast enough, launch your harpoon at it, and land the attack first time, there's a very good chance you'll catch one and get those skin fragments. The only downside is that there are usually some very aggressive fish near where the Cuttlefish are, so make sure you have something to attack them with.