Wanna get biotoxin without risking your Dinos? Find a school of these and get close enough to hit with a crossbow and aggro them - they’ll slowly swim closer. Draw them to a shore where you can stand and see them on the surface then shoot them with a gun. Once dead, check and make sure you didn’t miss any then harvest them with your axe. Gives about 15-18 biotoxin per jelly. Biotoxin spoils in an hour on you, 4hrs in a dino and 8 in preserving bin. Good luck!
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!