If you see a group of these bastards turn around and don't go back.. I just had a 206 spino and a 200 sarco get annihilated by a group of 4 of these and both tames had about 5k + health and it took merely 20 seconds for them to die... so stay away these guys are bad news!!!
Use a basilosaurus to fight them. Since all their attacks involve electricity unlike the electric eels which can bite, they are doing no damage to the basilosaurus. Just spam the attack button and don’t forget to harvest their body for toxin too!