From the Super Mario Wiki
Piscatory Petes are small Cheep Cheeps similar to Blurps and Rip Van Fishes. They appear in Super Mario World 2: Yoshi's Island and its remake Yoshi's Island: Super Mario Advance 3 in which they swim at the Yoshi, blocking its path. The Yoshi can defeat them in its Submarine form with a single torpedo.
They reappear in Yoshi's Island DS, although since the Submarine no longer shoots torpedoes, Yoshi simply has to avoid them. They appear automatically in the Island Museum the first time Yoshi views them instead of the normal "egg has to hit" policy. This is because Yoshi can't hit them with eggs.
"Piscatory" means of, relating to, or dependent on fish or fishing.
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