If one spawns 3 mantas will automatically spawn near it, and start following it and group up near its belly. If you feed a basilo every ichthy/megalodon/manta near the basilo will automatically take one damage (the game inflicts the damage as if it was inflicted by you), then get angry at you and start chasing you. You should then run away if your tame can't kill the mantas quickly because mantas do more damage through armor like saddles than other creatures, so your tame's health might get shredded in seconds.