These guys won't attack you unless you attack them. They will them group up and latch on to you, giving you the bleed effect.

I found a 4.5 size and fed it to a 150 Hesperides and it instantly tamed

If you attack one and don't one shot they will attack you I have noticed they won't if you kill one in one hit they will ignore you.

Will attack if you attack them, just stay clear of the water in general due to the amount of piranhas that spawn with them

Even if you only see one, keep an eye out for others after you've killed it.

Try not to hit them, because if provoked they suck your blood

U can get good blueprints when fishing

Don’t hit these if you just started trust me my 150 Kaprosuchus got mawled by these guys