Lenny is a light blue anchovy fish who has appeared in many episodes.
He is a light blue colored fish who wears blue pants, black shoes, a white coat, a red tie, and a black hat with a dark blue stripe on it. He wears a tuxedo every time he is with Mable-Monica. Sometimes he wears a white shirt. However, in "Spongicus," Lenny's tuxedo was shown without his head and his other look was there so it could possibly be that the other one is not Lenny or neither it was another fish because the tuxedo was only shown, not his head.
Compared to most anchovies seen in the series, Lenny, along with his wife Mable, are one of the few anchovies to speak full English, rather than the species' usual "meep" sounds.