Fish (Installation 05)
From Halopedia, the Halo wiki
A species of fish native to Delta Halo.
They can be seen at several points throughout the level Regret. It is unknown if they are related to any Earth species of fish, although this is unlikely, as they are in completely separate places.
It is assumed that they, like all species of animals on the Halos, were created or placed there by the Forerunner.