An interesting idea, but honestly I was very confused playing this, unsure of what I was meant to be doing and how certain mechanics worked, for example, I only realized from reading the comments that holding the mouse further from your fish makes it swim/dash faster, a detail that probably should have been in the tutorial (unless it was and I missed it?).
There were also moments were my shoal would randomly swim away from me really quick and I couldn't find them again, or one time they just all died at once even though there were no predators around. Not sure if these were mechanics I didn't understand or just bugs.
Again, a great idea, but the execution leaves a lot to be desired for me. I'd love to see it developed further though, taking these things into account.