In addition, since grayling are a freshwater species, the salt water of Cook Inlet serves as a barrier to potential migrants from the Susitna drainage. Maybe in time they would have colonized the Kenai system naturally. A short hop with a plane apparently overcame the obstacles that had stumped grayling for thousands of years. Blood lines, lateral lines, and other stuff Fish have many of the same internal organs that we do, a heart, stomach, liver, etc. But they have also developed some really neat physical features that are totally different from anything that humans have.
Fish have at least two internal organs that are misunderstood by many people.
Just as with our own kidneys, it filters the waste products of metabolism from the blood. These aid in the digestion and absorption of nutrients. Most people have probably seen the swim or gas bladder in a fish as they clean it. In salmon and trout it looks like a small, semi-transparent balloon inside the body cavity, right up alongside the kidney. Interestingly, it is actually the swim bladder of fish that is detected by the sonar units that we use in rivers for counting salmon.