Set the egg OSRS Items inside and wait until you own a fish (you can not put the shark puppy in it.) They help you catch fish underwater faster based on the stage. Stages are pup (there is not shark eggs), juvenile then adult. The next is that the Angler Fish. It's the only resource for light in dark underwater cave, as candles or lanterns would go out. They have three phases, egg, larvae and subsequently adult. You need to incubate the egg.
Pufferfish are the next. Their eggs are located on the surface of the water which you may get from scaling up the anchor rope. Climb it up to visit Captain Murk. Get a pufferfish egg and then incubate it. It will hatch soon. They blow up when an enemy strikes you, poisoning the enemy. The most common fish would be that the salmon. They help you find eggs. When you're in 10 squares of eggs, it is going to float in circles.
All fish have to keep underwater. You can not go from the water with it following you or on your stock. You may have just one fish at a time even if the fish is with the tamer. You can't go from this water with fish (besides eggs). Why you can't set them in the bank is because you have to give them to the Fish Tamer.
You might also have a house underwater in Mogrin. Your dungeon will be temporarily removed before you move your house to a location that is not underwater. Having a house in Mogrin unlocks a brand new attribute for the PoH. Whenever you're in Mogrin you can add an aquarium to your PoH. If you move your house, it will still be there and you can upgrade your aquarium items but you can't create another aquarium until you move back to Mogrin.
To make an aquarium, then you must have level 54 structure. When you put in your aquarium, you will see a hotspot which looks like a massive fish tank. To create it you must have level 54 construction, 3 regular boards, 8 claws and 4 molten glass bits. In this you can have 5 little fish or one medium sized fish. To get them, go Cheap RuneScape 2007 Gold to the Fish Tamer. Sorry people, crisis, gotta go, I'll update more later.