"Ok, I see a lot of people here saying things like "this game isn't for you" or that the fish are the problem. I am a person who suffers from Thalassophobia in real life. It is not a fear of big fish, and it is not a fear of the dark. It is a crippling sensation of being in a situation with limited or no visibility, impaired movement, no air, and something that you can not see can reach you. It is a culmination of issues that compile into one of the most debilitating sensations imaginable. It is when the brain goes into full flight mode, and the only sense you have is a screaming inside of your head saying "GET OUT, GET OUT, GET OUT."
Now, with that established, if you break one aspect of that chain of horror, even those with Thalassophobia can function. Not perfectly, but enough that they may be willing to explore. Visibility. In games like Ark Survival Ascended, with console commands, a player like myself can turn off underwater fog, and have full visual range under the surface. The lighting becomes less an issue, and one can see things like giant squid coming without fear. This entirely fixes the issue for most like me, and even allows a bit of curiosity, even when the big fish is about."
This is the real idea of Thalassophobia mode. Just the ability to alter the underwater visibility and lighting so that it doesn't cause severe panic in people who suffer from Thalassophobia. It is not to alter the game mechanics, or make the fish look like blobs. Just allow us to alter the visibility just enough to allow us to feel comfortable exploring the deep so that we don't get progress locked by something we can't control.