Sockeye salmon are an amazing species to watch during the time of their migration. These able bodied swimmers face the elements and forge against the raging waters of various streams to make their way back home to their breeding grounds. As if this journey wasn't enough, the salmon undergo huge physical changes to cope with the upcoming breeding season. As these salmon begin their upstream adventure, their bodies turn a deep red color. This coloration is how these salmon got their name suk-kegh (sockeye) which means " red fish" in Salish. The males of this species carry this metamorphosis to a new level by changing their heads to a deep green, and elongating them to expose sharp, jagged teeth.
You may be thinking that none of that is that amazing, but the real fascination these creatures provide comes from the changes that have occurred on the inside. Scientists have recently discovered that size and strength of an individual salmon's cardiovascular system directly correlates with the distance it travels to spawn. It seems that the farther a salmon travels upstream, the greater range of temperatures it encounters. To cope with the increase in water temperature the cardiovascular system must be enlarged to avoid fatigue due to this added stress. In a recent study it was determined that fish that spawn on the coastal boarders possessed a much smaller cardiovascular system, and were therefore much more susceptible to cardiac failure due to a change in water temperature.
These cardiovascular differences make sense for the species on an evolutionary level. It would be a waste for the coastal breeders to spend the energy necessary to maintain a larger cardiovascular system, if they very rarely faced dramatic changes in water temperature. While at the same time, the fish that travel up to 680 miles upstream need the evolutionary kick to get them to their breeding grounds.
Scientists are still unsure if water temperature was the original stressor for this evolutionary change. They hope to learn more in order to prevent unnecessary salmon deaths in the future because of the increase in water temperature due to global warming. If they are able to pin point the trigger to select for larger cardiovascular systems these fish may be able to breed in their traditional breeding grounds for many more generations.
Posted by M on Wednesday, April 27, 2011