The Japanese fish-shaped cake filled with red bean paste is taiyaki. It is a popular street-food confection made by pouring batter into a fish-shaped mold, adding sweetened azuki-bean paste, closing the mold, and cooking it until golden.
Taiyaki imitates tai, the Japanese red sea bream, a fish associated with good fortune and traditionally enjoyed on important occasions. The fish shape therefore gives the snack a celebratory symbolism as well as its name. Although anko is the classic filling, modern versions may contain custard, chocolate, sweet potato, cheese, sausage, or savory fillings.
Taiyaki first appeared in Japan in 1909. It is considered a reshaped version of imagawayaki, a round filled cake that predates it. That relationship explains why the two snacks can share similar batter and fillings despite their very different shapes.
Dango is another frequent mix-up, but dango consists of chewy rice-flour dumplings, not a filled fish-shaped cake.