I had a lot of fun playing this! Thank you for making it, I am definitely going to check out your other games.
It was enough fun that I was sad to complete it so quickly, so here's my feedback in case you make a longer version. :)
- Overall, I loved it: the premise, the incrementation, the aesthetics, the fishies, the joy of swimming around.
- I was mildly devastated when I became the biggest fish and suddenly could no longer swim! I wanted the joy of being a giant fish among little fish (as far as the demo goes) for some well-deserved carefree swimming at the end. Even if just for the demo, it would be nice if you could change it so you can keep swimming. It felt strange to upgrade the tree enough to be able to become the largest fish, but then have a lot of stamina wasted because I couldn't keep swimming upon reaching max size.
- Being unable to keep swimming as the largest fish squashed my desire to fully complete the upgrade tree (something I almost always do in incremental games). The more I filled it out, the sooner I was going to become the giant fish and be unable to continue individual runs.
- The mining addition was a fun, unexpected addition. While I agree with another commenter that it was a little awkward hold the mouse in place on an anchor while swimming, I felt like that was part of the fun. It added a layer of prioritization on whether to get metal or fish. I don't think that's necessarily a bad thing.
- Fish levels: Can you clarify which fish is what level. Do the levels apply to the player fish, or just the other fish? Is the starter fish level 0 or 1? Is the small blue fish level 1 or 2?
- Top of the screen says level 1. Is that indicating the player's fish level but not changing due to a bug? Or is it "level 1" as in "region 1," like there might be more regions later?
- It seems like there's very few fish and no anchors if you travel too far from the starting position. Is there a way to add more spawns in those more distant areas?
- Upgrade tree: Nice and easy to see tell if a node is maxed out, can be upgraded, or you don't have the resources to upgrade it, UNLESS you're red/green colorblind. Red/Green colorblindness affects ~4.5% of people. An additional indication on the maxed out green icons, such as an extra border or pattern could make it much easier for those with color deficiencies. Or a togglable colorblind mode which more obviously differentiates the icons could make it more accessible.
- More metal in the levels would balance the upgrade tree better. Despite purchasing and upgrading the ability to mine fairly early, I finished the fish-based upgrades well before I had enough metal to get more than halfway in the last two upgrade nodes that needed metal. Or maybe just a different biome to upgrade to that has more metal....
Overall, it was great to play and I look forward to seeing a full version!