Thank you for the feedback!
I see the point you're making and agree with it. It is not evident how to achieve it though. An idea I just had may be to have the lights of the submersible go out for a moment and make everything go completely dark. Then attract the player's attention on the radar and show that there is a mass approaching the submarine. When the player exits the radar view, the lights start up and make the swarm of fish visible, leading to an effect of wonder/suspense when seeing the mass approach in the radar and an effect of revelation when the attacking fish are first visible. Also I could change the intro to clearly show an approaching red mass rather than just a full red radar, I think it would be more effective in creating suspense, and there would be a parallel with when it actually happens to the player (the intro is supposed to depict the view of the first submersible that got lost). That would be a bit of work though.