Sushi is categorised as a type of Fish in Enchanted Folk and the School of Wizardry. It can only be found during Mystery Time.
Sushi appears to be a living version of a Nigiri Sushi, that moves when being held by a player.
Sushi can be caught in the ocean at The Beach or on The Island.
The sushi Catalogue entry reads:
"Some kinds of sushi fetch high prices."