Spectrum

From Memory Alpha, the free Star Trek reference

Spectrum was the name of a holographic Serosian fish that the HD25 Isomorphic Projection Dejaren created to keep him company. The Serosians didn't allow Dejaren to have the fish as a pet, so he was forced to hide Spectrum from them. (VOY: "Revulsion")

Spectrum was a porcupinefish (genus Diodon).