From Nookipedia, the Animal Crossing wiki
The hammerhead shark (シュモクザメ, Shumokuzame) is the most common member of the shark group. This large fish always appears in the ocean during the summer months, between June and September. The hammerhead shark has always sold for 8,000 Bells, except in the PAL versions of Animal Crossing: Wild World, where it sells for 12,000 Bells, as much as the Hercules Beetle or the newer Golden Stag beetle.
Donating to the Museum
When donated to the Museum, this fish always goes into the back tank, the ocean tank.
In Wild World
Blathers will comment on the player's donation as follows:
"The fin of the hammerhead shark is used in some foreign cooking, eh wot? Indeed, it is used in a delightful delicacy called shark's-fin soup! This dish is usually quite pricey because of all that goes into its preparation. Why, it takes three days merely to reconstitute the dried shark's fin! After THAT, the chef must pick out the skin and cartilage with tweezers! Only after all that can it be used as an ingredient. THAT is a just cost!"
In City Folk
Blathers will say this when handed the big fish:
"Ah, the hammerhead shark, also, I believe, known simply as the hammerhead in certain circles. The hammer-shaped head is thought to give this shark a great sense of its environment...like radar. Compared to other sharks, this one wears a bit of a daft expression that some people find charming!"
The hammerhead can then be found "pacing" in the back tank, much like the blue marlin.
In New Leaf
"The hammerhead shark is a shark with a head like a hammer, which is what you'd expect. However, despite being sharks, they are actually fairly laid back, which is not what you'd expect. With their eyes positioned on the two ends of their 'hammer,' they can see in almost all directions. Oddly, their nose holes are located right next to their eyes on their hammer section. They have a number of small holes on the front and lower portions of their heads as well. These holes allow them to detect prey, even fish hiding below them and out of sight. While they eat a nice array of fish, it seems rays are their favorite source of food. Rays, beware!"
The smooth hammerhead's name comes from its hammer, which lacks any sort of central indentation. It is a rather common hammerhead shark, and the second largest after the great hammerhead. It's fins are valued for the delicasy shark fin soup.
Names in other languages