Salmon are very unique creatures, in that they can live in both freshwater and saltwater environments. They live part of their short lives in the ocean and the rest of the time they spend in freshwater rivers and lakes. In a sense, Salmon live a double life in two very different environments. How are Salmon able to adapt to these two environments so easily?
Saltwater fish and freshwater fish each have different ways that they have adapted to their habitat. Saltwater creatures have to learn to compensate for the excess salt and other minerals in their body, while freshwater creatures do the exact opposite. They have to make up for the lack of minerals and salt in the water.
Saltwater fish have to consume a lot of saltwater in order to get enough water to survive. The excess salt then has to be expelled through active transport via the kidneys and/or the gills. The urine of these animals are highly concentrated with salt and other ions and it does not contain much water so as to conserve it.
Freshwater fish do not take in or drink any or very little amounts of water, because they are surrounded by freshwater and can take in too much water if they drink it. Freshwater fish obtain the salt that they need from their food. They will eat things that have the salt and other ions that they can’t get from the surrounding water. In contrast with saltwater creatures, their urine is very watery so as to get rid of the excessive amounts of water they take in.
Salmon are born in freshwater so they easily adjust to it, but when they enter the ocean they produce something called cortisol which stimulates the growth of chloride cells. These cells excrete salt which is then excreted through the gills. Once they renter the freshwater streams, Salmon just stop producing cortisol so they can adjust to the surrounding environment again. Salmon are amazing and unique creatures, because they can easily adjust between two very different environments.