Question

Bony fish that live in freshwater use what to get rid of excess water ?

Answer 1

They use the algae in the water                                                           

Answer 2

Many fishes excrete Ammonia which takes a lot of water to be removed !! All the excess water are excreted out either through excretory system or by gills !!

Second they maintain ion balance by gills by uptaking ions by active transport !