Hey, the fish die because you have to go to supplies & purchase environment upgrades and different things like an aeration system. So in the beginning, or if you already have $500, go to supplies and do environment. Wait an hour or so on 2 x speed for it to complete. Then you can breed more fish. Once you have money from that, you'll be able to get the oxygen & the food upgrades & have enough $ upgrade the last time and breed anything. Make sure you get the aeration system once you get to the level 2 env. It is fun doing the charts, aint it?
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Yaelle