An alternative given (and the only one available on the wordbank) is "The fish is in a floor". Unless they mean a fish in a mosaic, how can this be a correct sentence?
Add your fish to the contents of a concrete mill, mix and poor. Or if you are rich and obsessed with fish, get aquarium floors.
Though I agree it is not realistic and a bad translation.
Reported via the "hover hints are wrong" option - as the others say: the preposition should be 'on' not 'in'...it looks like a typo - I often type 'i' for 'o' and vice versa.