The best thing to do when you need fish meat is to find a Piranha. First, you go into the water by about, 4 ark inches. Second, you go on shore. Third you take a look at the water. Last, if (IF) there are Piranhas there, kill em’. In my opinion the best thing to harvest the fish meat with is a pickaxe.
These guys can be tamed with the aberration fish basket but dam, this thing is annoying if you want to swim without any dino, taming one with an ab fish basket is 100% useless plus it's the most annoying thing ever for new players, but if you tame a high level army of these it can be op tho
These things will spawn in your water pen and kill your tames if they're on passive. Make sure you have Dino's to kill them or foundations all around your pen, they've killed so many of my Icthyosaurus' it's not even funny.
Be very carful while crossing the smallest rivers, they might seem weak but usually around 3 of them comes. They also have a pretty big range.Spear can take one of them but for multiple you are going to need a decent armor and a pike.
I'm around lvl 30 and ever since I started the game I can honestly say "I hate these creatures!" I've died by them more then anything else lost two parasaurs, a raptor, and who knows what else. Advise keep glancing under water to see if any are around, avoide rivers crossing on foot. I like rock hopping and dino swimming they can take more damage
If you’ve got a sheer enough drop off into deep water, these are easy and hilarious to kill. I was dehydrated in a cave one time, stepped into the water to see 20 of these guys turn to me, stepped out and they all popped out after me. They die the second they hit air.