While your tame still might die anyway if you have a high hp dino that gets zapped by these whistle followall and swim away. If you can i managed to rescue my 140 rex that way. She had 8k health and lost around half with a normal saddle. I came back with my re and killed them with rock throw. (It was super effective)
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!