Use a school of Sabertooth Salmon and harvest them with a sickle to get a better chance at prime fish meat when you spot one. For the best results go for one around level 90 or above if you can, and make sure you have at least 125 narcotics on you when you knock it out. It can be a lengthy tame due to the overall tame percentage gain of fish but having a few of these with about 3k health and the rest of their levels into power makes them a nightmare, especially in water due to their stun. Enjoy, they're a favorite of mine.
I would argue that this dinosaur is the strongest mount that can fight on both land and in the water. I had one that was bred multiple generations, full imprint, purple saddle. I named him Fury to represent all of the anguish I experienced leading up to his creation. He was able to handle anything I threw at him with ease. People were surprised to hear that I was easily able to kill both squids and alpha carnos with him. Never got to attempt an alpha Rex. He met his match when I attempted an alpha squid. RIP Fury.
Baryonyx are quick like Allosaurus and do just as much damage (but don't get a pack bonus). They don't use oxygen for swimming and can sprint in the water. Right click in the water does an AoE stun that lasts about 10 sec. Their 'C' is a... Taunt? They also jump and you can fire a weapon from their back.
These are great for doing fish meat runs. Most water mounts such as Basils, eat fish meat as fast as they can gather it. Others such as spinos simple are a pain to use in underwater combat due to turn radios and hit box. Baryonyx gathers fas much fish meat as a spino, but better due to its stun ability and unlimited oxygen and maneuverability. Just swim right up to a megladon, stun it, chomp. Rinse and reappear. Best at fish meat gathering in my opinion. Never underestimate their stun ability!!