Cyclicthys is a genus of fish in the porcupinefish family, Diodontidae.

Fish of the genus Cyclicthys have three-rooted, rigid spines (actually modified scales) distributed over their bodies, and beak-like jaws, used to crush their hard-shelled prey (crustaceans and molluscs).

[1] They differ from members of the genus Diodon, which have moveable spines.

Their inflated size combined with their spines make them extremely difficult to swallow.

They may be poisonous, through the accumulation of tetrodotoxin or ciguatera.