Hi, I'm Lauren Stern. Hi, I'm Vivian Tron. And we are KnifeGrid students in Miss Andrew's seventh period Biology Honors class. The question that we received from the middle school students was how do freshwater salmon survive in the ocean? Freshwater salmon has been most of their life in the open ocean, living in the Northern Atlantic Ocean and the Pacific Ocean. They are an adromus, meaning that most types are born in freshwater and then they migrate to the sea and then return to freshwater to spawn. As adults, they lay their eggs and gravel beds at the upper reaches of freshwater streams. And when the eggs hatch, the salmon spends several months migrating downstream to the open ocean where they remain for some three to five years. When mature, the adult salmon return to the mouth of the stream where they originally hatched and migrate upstream to its head waters, spawn and die. While in freshwater, the fish are hypertonic to their surroundings. This means that their cells have a lower water concentration than the surrounding freshwater. Without certain adaptations, the cells would absorb so much water during oxmosis that the pressure would build up and the cell would burst. While the salmon are in salt water, they are hypotonic to their surroundings. That means that their cells have a higher water concentration than the surrounding sea water. Sea water is made up of the salt which is dissolved into the solvent water. This ultimately means that the ratio of salt to water is greater than the ratio of salt to water in freshwater. Without certain adaptations, the water would leave the salmon cell and the salmon cell would ultimately shrink and its contents would also be compressed, making it harder for the cell to carry out certain functions. And this happens through the process of oxmosis as too much water has left the cell to dilute the salt water outside of it. In freshwater, the freshwater will move into the cell because the membrane is permeable only to water and instead of salt moving out, water moves in. In salt water, water would move out of the cell in an attempt to create an exotonic concentration on both sides which means that the concentrations of salt and water are the same on both sides of the membrane. In order for salmon to stay hydrated well in salt water, the salmon drink sea water to replace the water that they've already lost. However, a consistent problem occurs where the salmon must filter out the salt so that it doesn't affect their cells. One of the salmon salt water adaptations includes the kidney's ability to produce concentrated urine. This means that the fish can get rid of large amounts of salt while using minimal amounts of water. The fish contain a special enzyme in their gill that uses energy from breaking apart molecules to actively transport salt against their concentration gradient out of the blood and into the salt water. In summary, while salmon are in freshwater, they can see a large amount of freshwater which must be diffused into their bloodstream biosmosis. While in salt water, the fish cannot afford to lose any more water. Therefore, it must produce small amounts of concentrated urine as well as X-Great salt-thru-it-skills. The end! Thank you for watching!