Very neat game. The thing I liked about it most was the variety--both in the number of fish, but also in level design, including the different ways oxygen was sourced, and the different settings themselves.

Level 2 feels legitimately scary, partially because of the music but also because there is only one tiny oxygen source for exploring the whole area. It feels intense because every scan is somewhat slow and so you have to take it quite slow, often getting more oxygen after scanning a single fish. (Which does make it tedious, but I imagine that's the point?)

Level 3, on the other hand, feels more upbeat and joyous like its music suggests, as oxygen is plentiful and it is easier to navigate. There's also more clustered fish / kelp which makes scanning more fun as you can get multiple done with one scan.

I did find a number of points of confusion while playing.

• It took me a while to figure out how to actually end level 1. Going to the location marker itself did nothing, while I couldn't seem to find my way into the tube. Eventually I managed to get myself off the ground far enough that I could actually get into the tube, but it wasn't obvious that that was where I was supposed to go. I think putting the location marker at the end of the tube rather than at the front would go a long way for clarity.
• In level 2 I would sometimes see some kind of damage markers (?) appear, but I have no idea why. They always appeared when I was generally full on oxygen. My best guess is that it's cause I ran into the lionfish? But I'm not sure.
• I couldn't find "Fish name" in level 3. I had read the itch.io description multiple times before I finally realized that by "Rock Coral" doesn't appear correctly in the progress menu" you really mean "Rock Coral appears as "Fish name" in the progress menu." I think saying that in the bug description would be very helpful. Part of the problem is that one of the rock corals in the level simply refused to scan at all, so I might have thought they were unscannable.
• It's not clear what the "MAIN MISSION" button on the pause menu is supposed to do.

As a nitpick, I feel like making me breath manually while above the water in Level 3 didn't make sense. 

I think the core concept of forcing multitasking is always a fun one. I definitely did not get particularly good at the multitasking by the end of the game, and so it's always interesting just how hard it can be. I found I often mixed up left and right click... I would be trying to release the scanner but accidentally stop breathing, or be trying to stop breathing but accidentally release the scanner, etc etc. So it's interesting because I would argue the scanner button specifically does more as an additional point of confusion than as a particularly compelling player input on its own, which is kinda neat.

Overall, even if there are some rough edges, this is a very impressive entry for the jam. The sheer variety of content is enough to make it fun--simply exploring these different environments with different vibes is engaging. Great job!