Great game with a good, fun and addicting concept! Could be improved a lot though. It's pretty pointless to have all the upgrades upgrade the same thing, at least they all say they improve only rare fish chance. Maybe you didn't have enough time to do different upgrades? Because currently there is no strategy to buying, you just buy whatever is the cheapest. There could be something which reduces wait time for getting fishes, increasing fish value etc.
Also the aquarium could be improved a lot. The fishes generate barely enough money to make a profit, unless you play for a long time. Also I don't know what the point of the feeding is, the fishes are alive for 20h and no one is going to play for that long.
Those things would already make it a lot more fun to play the game for a long time. I wanted to try and max every upgrade but gave up cause I got too bored when nothing new happened. So more areas would also be great. And I wonder what the two secret achievements are, couldn't figure them out.
But yeah for only 7 days of time and working solo, this is really good, well done!