This one is a great game! I liked a lot the concept of diving deeper to fight mechs, also the fact fishes are essentially aiding you in your mission by providing light! I liked the dub a lot. I loved the fact that there's a minimap: I tend to get stuck on levels, but with this one it wasn't the case! The big mechs are so menacing when they appear, and they made the fight truly epic!
Some critiques I have now: first of all, the player feels slow. The controls seem a bit too slippery, and I had a very hard time dodging bullets, but I get this might be part of the difficoulty (and the theming, because obviously in water it won't move as fast), so maybe adding a dash or run-like ability would be nice to have. I liked the fact there were two projectiles at first, but at the introduction of the disabling bullet I began to think maybe a second projectile is just confusing. I found myself using it only in a few occasions, and due to its long cooldown I mainly used the more spammable bullet. I would think maybe merging the disabling bullet and the big bullet would be optimal, maybe balanced by a slightly longer delay between firing the big bullet and the small bullet, so the player would have a choice of using the bigger, useful but slower bullet and wait a while before he can use the small one, or use the small, spammable one, that cannot disable shields (and would not be encouraged to hold both mouse keys to shoot both at the same time). I would also like to know when the big bullet's ready, maybe a visible timer or loading bar would do. Also one last small small nitpick: the big mechs look blurry most probably because you didn't put "filter mode" to "point(no filter)" in the mech's sprite in Unity, but this is easily fixable by either doing that, or scaling the big mech's sprites.
The music is great, tho I would've liked a more action music for when a big mech appears (but I understand it's not easy to compose in just 7 days).
Overall this is a great game, I could see myself returning to it if it ever gets updated! The gameplay loop is very fun, and the mech designs are simple but perfect! Great work, can see it becoming a bigger game! :D