Fish (High Ground habitat)
From Halopedia, the Halo wiki
A species of fish native to Earth.
One of their defining characteristics is an odd snout, distinguishing them from other fish.
On the level High Ground, one can find small fish in the water. It is possible to kill them; if you do, they float to the surface and then drift to shore before eventually respawning. Throwing a grenade in the water will result in the whole school dying and floating to the surface (like throwing dynamite in a pond).