Taming this guys are easy, all you need in an Ichthyosaurs 2 stacks of Raw Meat and a Will to go to ocean bottom. Set your Ichthyosaurs in passive , swim to one and make sure you are on the left side of the basilo so that when you jump off the basilo is in feeding range.
Feed it and jump back on the Ichthyo lure the mantas and the baddies away from basilo. After the drop agro go back and feed again. Always remember to get off the Ichthyosaur right beside the basilo so you can feed it and jump back on it and run to safety. Be cautious of your surroundings especially Tuso and don't forget to keep eye on oxygen all the time underwater
I tamed mine with a baryonyx to kill the manta bodyguards. The time between the first and second feeding interval takes a while, so sit back and grab some coffee while you wait. Regular meat will do as after the second feeding, the interval is only about 10 seconds. Make sure you keep all Megalodons and other mantas away from it while taming. I absolutely love mine for alpha killing and bio toxin farming. Also they get a crap ton of hit points per level up, almost 400.