SOMA Enemies (major spoilers)

[Potato]

While the logic calls #5 Akers, the story says there's at least 3 of them roaming around. Then again, since it's made from several people, maybe parts of Akers are in all of them.

I searched all of the game's files, no occurences of "Jiangshi" found.

I think it's fair to refer as #5 as Akers, since the enemy found in Theta labs is intended to be one, singular enemy (Akers), whereas #4 is Akers' little kin that are referred in that specific note you were talking about. More than one (at least 3 iirc) are encountered in Maintenance. The Proxy in Theta labs is specifically referred to as Akers in the script multiple times as well (He also has a lot of voicelines!)

Any idea what the aggressive fish in the abyss are called? That's the last thing bothering me.

I think we can just refer to them by their entity name, which would be Viperfish. In-game appearance, Model in Model Viewer