Blue marlin

One of the most expensive ocean fish, the Blue Marlin (カジキ, Kajiki), despite appearing all the time in late summer, is actually very hard to find. Selling for 10,000 Bells, this fish resembles a swordfish. It has a long, pointed extension of its mouth. The fish can be found all day and has a large shadow size.

Donating to the Museum
When placed in the museum in all games, the fish goes in the very back tank and zips around very quickly.

In Wild World
Blathers says this about the blue marlin when donated:

"To be honest, this is the first time that I've seen a proper blue marlin, wot wot! As you can see, its bill is quite dangerous. Every year people are injured by them. Still, how can one complain? If you were to drag me out of the museum one night... I assure you, I would give you a pecking you'd not soon forget, hoo!"

In City Folk
Blathers will talk about the blue marlin when donated:

"Hootie hoo, what a magnificent fish! Look at that sleek, hornlike bill! This fish is quite fast, said to be capable of reaching speeds of up to 100 kilometers per hour... A regular oceanic speed demon, wot? If you get in its way, beware! It might not be able to stop in time!"

In New Leaf
"Blue marlins are famous for their long, swordlike noses that give them the nickname 'swordfish.' They use their 'swords' to knock out their prey before capture, not skewering it as you'd think. Able to swim at speeds above 60 mph, their speed and power make them a true test for any angler."

Encyclopedia Information
Once the player has caught a particular fish or bug, they can find information about it in the bug or fish menus. Once the blue marlin has been caught, the following information can be found in the fish menu:

Further information
The Animal Crossing blue marlin is actually the Atlantic variation. In the wild, it uses its big spear-like snout to attack fish and cepapholods that it may eat, such as tuna and squid. Represented in-game by the fact that it only appears in summer, the Atlantic blue marlin generally stays in the area of ocean south of Spain but north of South Africa. There are many names for this fish such as billfish, ocean guard, and Cuban black marlin.