Napoleonfish

The Napoleonfish (ナポレオンフィッシュ, Naporeon Fisshu) is a big, blue, rare fish with a large humped head. One of a group of fish which all sell for 10,000 Bells, this fish appears during late summer in the sea and island sea. Like most other sea fish, the Napoleonfish appears in the back tank, when placed in the museum. Its first appearance is in and it also appears in  and.

In
In, the Napoleonfish is a lucky item during summer, meaning it gives a 777-point Happy Home Academy bonus when placed in the player's house.

In
Upon donating the Napoleonfish to the museum, Blathers will comment:

The Napoleonfish can be found lazing around near the bottom of the sea fish tank at the back of the fish exhibit.

In
After donating a Napoleonfish to Blathers, it will appear in the section for fish and sea creatures, specifically in the large tank in the northeastern room of the fish and sea creatures area.

The exhibit has this to say about the Napoleonfish:

In
Once donated, the Napoleonfish can be seen in the coral reef tank with the Clown Fish and Butterfly Fish.

Real-world information
The Napoleonfish, Cheilinus undulatus, is more commonly known as the humphead wrasse; both names are derived from the large hump on the forehead of adults. Males are larger than females. Due to overfishing and the destruction of coral reefs, their natural habitats, the fish is now considered endangered. Humphead wrasses are protogynous hermaphrodites: all fish are born female, but contain the genes for both sexes, and some fish change sex to male a year or two after sexual maturity.