How Dolphins Get Fresh Water While Living in the Ocean

Dolphins and other cetaceans get most of their water from food, while breaking down nutrients also creates extra metabolic water inside their bodies.

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Living in the ocean creates a strange hydration problem for marine mammals: the surrounding water is salty, while their bodies still need usable water. Research on cetaceans shows that food and metabolism are major parts of the solution. Water already contained in prey provides a substantial supply, and cells also create metabolic water as they break down nutrients such as carbohydrates, proteins, and fats. A 2023 study using oxygen isotope measurements in bottlenose dolphins and killer whales found that dietary water and metabolic water together accounted for more than 90 percent of total water input in the animals studied. The remaining input was linked to inhaled water vapor and surrounding seawater that was accidentally ingested or absorbed. The study also found that metabolic water was more important in animals eating more lipid-rich diets. This helps explain how cetaceans can maintain their water balance in a marine environment without relying on freshwater drinking in the way humans do. Older research has also found evidence that dolphins can consume some seawater, so the picture is more complicated than simply saying they never ingest salt water. The key point is that food water and water produced internally through metabolism make up the dominant sources measured in the modern study.

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