The Titan Holefish is based off the ocean sunfish.

Slow, stupid and "delicious", they mindlessly swim around the icy cold water. They have completely zero reflexes, doesn't react to any form of danger at all, since they completely relied on symbolic Symbiotes.

The most significant feature about them, is, you guessed it, the hole. The hole is lined with oxygen-rich gels which you can absorb as an emergency oxygen supply. They provided oxygen and nutrients for the Symbiotes' eggs. In return, these small aggressive fishes would do anything to defend these derpy "titans", as well as feeding them and thus cleaning off parasites.

P.S. I called them "derpy" because they're literally brainless-- they're so stupid they didn't even react to getting RAMMED by a Seatruck submarine


Edit(31/12/2021)--Fixed a few minor mistakes in my previous post:
-The symbiote on the hole was "through" the gel
-The rear fin of the Titan Holefish was "seenthrough" the body
-Background light rays were too close together
-The quartz didn't "luminate" correctly