Easy bio toxin: Just find one near the shore, aggro it and swim to the shore, making shore its following you. Once your on the shore wait for jellyfish to be on the edge of shore and just stab it with your spear / pike. You get like 20 - 30 bio toxin, but 1 spoils in about 40 minutes. I find it really useful to just go harvest bio toxin than use narcotics to keep a tamping Dino asleep, so you can use all your narcotics on tranq arrows or tranq darts. Oh and finally once you reach a high enough level (I think around level 90) you can learn the shock dart which uses the bio toxins, and 1 - 3 shots most Dinos.
Using a quetzal, kill the ones on the surface for easy bio toxin, then use it to make shocking darts, which are better than tranq darts, or use the bio toxin as a better narcotic for being Dino's torpor up
They drop a pretty neat resource called 'Bio Toxin' when killed. It can be use as a steonger alternative to the Narcotic. It can also be used for a new 'Shocking Tranq Dart' which can shock the target and add a substantial amount of torpor. Perfect for knocking out Quetzal's.