I love fish, but even foods that are fish-shaped are fun!
Taiyaki is a Japanese snack which is comprised of a fish-shaped waffle filled with sweet red bean paste inside. Although red bean paste is traditionally used, other fillings such as custard, chocolate, and vanilla also exist. They are best eaten freshly made, hot from the street vendor.
I’ve only eaten Taiyaki in Japan, but I’m sure Taiyaki is available in areas with a sizable Japanese population. This snack originates from over 100 years ago.
As an odd fact, the band Aerosmith loves Taiyaki (as I have read on the Japanese Wikipedia entry)!