This is a very creative game. By registering my mutated fish, I can increase the variety of new ones that I can purchase. This means that there is no limit to the types of fish I can purchase. It's really exciting!
This game reminds me of Insaniquarium or Cookie Clicker, but I feel it has even greater potential.
Once I can register a 'strong' fish, I feel that the space occupied by weak fish in my aquarium is wasted. I would then delete the weak fish in the trash. If I do so, and add stronger fish, the aquarium will become 'stronger'.
However, in doing so, the aquarium temporarily loses its diversity. This is a bit of a contradiction, because it is more visually pleasing to have a variety of fish in an aquarium.
Insaniquarium had a concept like an ecosystem to solve this point. I think that special interactions between different species would make this game even more fun.
Anyway, it's a really interesting concept!