1) Depending on the salt concentration, fish either drink water (like marine species) or abstain from it (like freshwater ones).
2) Their gills and kidneys are able to rebuild from one way of osmoregulation to another: in seawater they have the same osmoregulatory system as in marine fish, in fresh water – like in freshwater ones (their blood in seawater is hypotonic, and in fresh water it is hypertonic ).
3) The reserve fat accumulated in the body of the fish helps them overcome rapids, waterfalls and fast counter currents, providing energy.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.