These are the most violent creature in game. You need at least 3 people, 10 Gigas max level, a platform quetzal, with cannon balls about 250 minimum. A couple rex's hopefully max level health. Now build a simple trap out of metal spikes. Now find one of these beasts, very carefully line up your Gigas, and rex's. These are sacrifices for the Coelacanth to eat while you shoot carefully from your queztal, have the other people shoot as well. Finally feed the beast kibble.
So how to really tame it get a fish basket then find one you like then put the fishing basket in front of it then when it gets close press capture fish don't know why people keep lieing about how to tame it.
Trap coels in a fish basket, then cryo the fish. Keep them cryoed until you want to tame a shadow, then make another fish basket, release them from the cryo and trap them again. Put the fish basket in your hot bar and submerge yourself to reset their timer. No wasting fish baskets. Get lots of fungal wood to make more baskets as they will destroy after you "tame".