Their attacks shock you (which makes you unable to move), and they often stick in groups. If you get surrounded by these, you're basically dead. Don't use melee weapons, use a crossbow.

They drop bio toxins, which can be used for a new tranq dart that's more powerful AND shocks the target.

All fish can't kill you in shallow water!
Just make them come in shallow water and kill them with bare hands!
Believe me!
These f#cking creatures can't shock you in shallow water
Make sure they are very near to the beach and kill them!

Once grabbed they won't let go till dead I had a Lvl 215 spino and was having a jolly swim then BANG WAM I get jumped by 8 jelly bastards and the spino died :(