Which process facilitates osmoregulation if a saltwater fish migrates from the ocean into a freshwater river?

💡 Explanation

When a saltwater fish enters freshwater, the external environment becomes hypotonic; water diffuses *into* the fish's body while salts are lost to the environment via osmosis. Kidney tubule salt reabsorption decreases minimizing salt loss leading to increased dilute urine production to excrete excess water. Therefore lessened salt retention results, rather than altered gill excretion or more water intake behaviors required by saltwater or blocking all water by the scales.

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