"Man's Best Friend"

An egg can be found in the Deep Grand Reef on the floor inside the Degasi base, pick one up whilst you're down there for Seamonsters. There are only 5 eggs in total though, and it may be possible to lose one - so technically this is missable although it'd be hard to miss it.

To hatch it, you need to build an Alien Containment unit in your base, with a hatch so you can get in and out of it. Once built, place the egg inside and it'll take about 20 minutes to hatch. After it's hatched, pick up the cuddlefish then go outside and drop it to release the fish.

NB you'll need 5 glass, 4 titanium and 1 quartz to build the alien containment and the hatch.