Taiyaki is a fish-shaped Japanese pancake stuffed with sweet red bean paste.
Taiyaki is made using fish-shaped mold.
Main ingredient of batter is wheat flour.
Nowadays, there are some taiyaki filled with custard, chocolate, or other ingredient instead of red bean paste.
By the way, "Tai" means sea bream.
Sea bream is a high quality cooking ingredient for Japanese dishes.
I supose it is why they made sea bream-shaped pancake.