What physiological characteristics of anadromous fish allow them to make long migrations associated with changes in water salinity?

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.

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