Raw tuna are fish that can be caught with level 35 Fishing or level 55 Fishing if catching barehanded, granting 80 Fishing experience per catch. It can be cooked into tuna with level 30 Cooking, granting 100 Cooking experience on a range and 110 Cooking experience on a bonfire. Raw tuna are caught through harpooning, which requires either a harpoon or sufficient Barbarian Training. The fish are caught with the Harpoon option at Cage/Harpoon fishing spots found by the sea.
Free players generally only fish tuna at the dock on Musa Point. Members generally fish tuna at Catherby or the Fishing Guild. Since swordfish is also caught at the same fishing spots, tuna are sometimes seen as a nuisance by players seeking swordfish; thus, it is often seen dropped by Cage/Harpoon spots. At level 35 Agility it is possible to catch two raw tunas at once, but you will only receive experience for one tuna. If two tunas are caught at once a message will appear in the chat box stating, "Your quick reactions allow you to catch two tuna."
Karamja: Behind Luthas' banana plantation on the northern part of the island is a small dock that has fishing spots where players can harpoon, cage, or net fish. Unfortunately a bank is very far away and players have to pay 30 coins to go to the island and 30 coins to leave the island. Stiles can note raw and cooked fish, allowing the player to stay on Karamja and fish indefinitely without banking. There is a bank deposit box next to the Monks of Entrana in Port Sarim. Players still have to pay the thirty coins back and forth from the island, but it's a closer walk than to a bank.
Wilderness: At level 35 to 38 in the Wilderness are some harpoon and cage fishing spots in the waters at the eastern edge. However, player killers may attack and disrupt the player. Players who are training in the Wilderness may use this spot for food, as one of the trees south-west of the fishing spots can be cut and lit to use for Cooking.
Catherby beach. Close to a bank, range, and also a fishing shop, this area is the most popular place for lower-level players and skillers to catch lobsters or swordfish.
Fishing Guild: The Fishing Guild has many Cage/Harpoon spots and is very close to a bank and a range, and there are spawns of a harpoon and a lobster cage nearby as well as a fishing shop. It is preferable for fishers with 68 Fishing or higher, though some players still prefer to fish in other places such as Catherby. With the help of a fish pie, fishing potion, or admiral pie, the guild can be accessed as low as level 63; however, if a player logs out in the Fishing Guild without the required level, they will log in outside. Keep this in mind if you plan to use these boosts with an unstable Internet connection.
Jatizso: Accessible after starting The Fremennik Isles, this spot is frequently deserted despite being as close to a bank as Catherby. It's not quite as good as the Fishing Guild, but it's a fine place to cage or harpoon.
Rellekka: Far from a bank and not in a convenient location. However, if a player equips Fremennik sea boots 1 or up, the player will be able to deposit their catches at Peer the Seer, located north of the Fremennik market, making this a fairly good place to fish. Conveniently there is an everlasting fire in Yrsa's clothing shop if a player wants to cook their catch.
When a player reaches level 50 fishing, they will also catch raw swordfish from the same spot. The approximate percentage of tuna and swordfish for a player with 99 Fishing, catching 4500 fish will be 51.73% for tuna and 48.27% for swordfish.