Spiny Cheep Cheep

Spiny Cheep-Cheeps are blue Cheep-Cheeps with spikes running down their backs. They only appear in one level, 7-4 on Super Mario Bros. 3 but swim faster than normal Cheep-Cheeps. The spikes don't really make it more dangerous, since Mario and Luigi can't stomp on enemies underwater anyway.

They reappear in Super Mario Land 2: Six Golden Coins. This small variety was colored black and acted similar to its Super Mario Bros. 3 counterpart.

After a long hiatus, these fish reappear in the game New Super Mario Bros. Wii where they are now purple. They will home in on the character and can only be defeated with a fireball, being frozen, or by a Star.

Trivia

 * A very similar fish appears in Yoshi Touch & Go, as it was blue and spiky, but this unnamed fish's spikes were white, and were always seen jumping. They could only be defeated by smacking them with an egg, and is actually most likely a spiky variant of Flopsy Fish.
 * Spiny Cheep-Cheeps are set to make an appearance in New Super Mario Bros. Wii.
 * In Super Mario World there are blue spiny fish which cannot be defeated except by Invincible Mario and they try to get beneath Mario or Luigi so that the character will land on them and die.