Covenant koi
From Halopedia, the Halo wiki
Covenant Koi (tentative name) are a species of fish similar to Earth Koi and Goldfish.
The Covenant apparently make similar use of them as Humans do of their counterparts, namely that of a decorative pond fish. A school of fish was kept in a garden in High Charity.
They can be found on the level Gravemind, in the central pond of the Valley of Tears B section within High Charity.
