Case #6 — A Fishy Tale You read a news release indicating that a species of saltwater fish was found in Lake Michigan. How it got there was a mystery. Unfortunately, the fish has died. In another instance, a saltwater fish was found living in a lake a bit upstream from the Gulf of Mexico. It was assumed that the fish swam from the ocean to a freshwater lake. This fish survived and is doing well in the lake. You wonder why one fish survived and the other did not. (Be sure to include specific biological terms such as hypotonic, isotonic, or hypertonic in your explanation. Also talk about the water relationship between the cells of the fish and the water outside.)
Questions:
1. What happened to the saltwater fish that was found in Lake Michigan?
2. Explain what happened to the survivor fish that swam from the Gulf of Mexico to the freshwater lake. (Hint: the journey from the ocean to the lake will take the fish through some brackish water—water that has more salinity than freshwater but less than salt water.)
3. What would happen to a freshwater fish that suddenly found itself in the Atlantic Ocean? Explain.
