From Nookipedia, the Animal Crossing wiki
The Squid (イカ, Ika) is a fish that can be found in the ocean between December and mid-August, at any time of the day. Despite its being called a fish in Animal Crossing series, it is, in fact, a type of mollusk, like (but not directly related to) the Octopus.
Donating to the museum
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.
In New Leaf
The information board in front of the tank that houses the Squid says the following:
Chip will say this when given a Squid:
The type of squid in Animal Crossing is not 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 referred to as the inshore, calamari, and grass squid. Squids eat small plants, insects and small animals that float on the surface of the ocean.
Names in other languages