Squid

The Squid is a fish that can be found in the ocean between December and mid-August, at any time of the day. Despite it being called a fish in, it is infact a type of mollusc (Europe) / mollusk (US) , like (but not directly related to) the Octopus.

Donating to the Museum
Squid can be donated to the museum: when given to Blathers, he will briefly talk about the Mollusk.

In Wild World
"Octopus and squid both have ink, and I've seen squid ink in recipes quite often... Strangely, however, I've never heard of a dish that uses octupus ink! I suppose it's partially due to the fact that octopi produce very little ink... What ink they DO make is watery and ill-suited for cooking, as well... That said, I've heard that the flavor is not at all repugnant, eh wot? Perhaps an octopus-ink pasta wouldn't be bad..."

After being given to the museum, the squid will appear in the ocean tank of the aquarium, propelling itself around towards the back.

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 squid has been caught, the following information can be found in the fish menu:

Further Information
The type of squid in Animal Crossing isn't mentioned, but judging by the in-built City Folk description, it maybe a European Squid which is white with two long arms. The family name,  'Loliginidae'  is commonly refered to as the inshore, calamari, and grass squid. Squid eat small plants, insects and small animals that float on the surface of the ocean.