Afish controls the concentration of salt in its body by actively excreting salt across its gills, drinking, and producing very small amounts of concentrated urine.

The answer is hyper-tonic.

Explanation:

The hyper-tonic fishes are found in freshwater. In these fishes, their blood conveys a lower water focus than the encompassing freshwater. With the death of freshwater by means of the mouth over the layers of the gill, the particles of water diffuse from the freshwater into the blood as a natural side effect.  These fishes need to create an extremely tremendous amount of pee to offset this abundant utilization of water. These fishes therefore deliver little measures of concentrated pee.

from the original order (top to bottom) the new order will go

1 (founder)

4 (hawk)

2 (mutate)

3 (next generation)