What effect does osmosis have on freshwater fishes?

Osmosis significantly affects freshwater fishes due to their hypoosmotic environment, where the surrounding water has a lower concentration of solutes than their bodily fluids. As a result, water continuously enters their bodies through osmosis, leading to potential overhydration. To counteract this, freshwater fishes actively excrete excess water through their kidneys and produce dilute urine, while also absorbing salts through their gills to maintain osmotic balance. This regulatory process is crucial for their survival in freshwater habitats.