Here's why:
* Osmosis: Saltwater minnows have adapted to live in a high-salt environment. Their bodies are designed to maintain a balance of salt and water. If placed in freshwater, the water would rush into their bodies, diluting their internal fluids and potentially leading to cell damage and death.
* Physiological Adaptations: Their kidneys and gills are specifically designed to handle the high salt levels in seawater. They can't efficiently process the low salt content of freshwater.
In summary: Saltwater minnows are specially adapted to saltwater environments and cannot survive in freshwater for extended periods.