What information have conservation physiologists uncovered about possible reasons that some sockeye salmon breed successfully while others are unsuccessful at reproduction?

Question

What will be an ideal response?

Answer 1

Answer: Sockeye salmon are anadromous young hatch in freshwater rivers, then several years later migrate to the ocean where they continue to grow and mature before migrating back to their birthplace to spawn and die. When salmon move from saltwater to freshwater, their gills must undergo a transition from an ion secreting epithelium in saltwater to an ion absorbing epithelium in freshwater. When the shift between the two types of epithelia occurs, there is a change in the expression of genes that encode the sodium-potassium pump. The isoform, Na+/K+ ATPase α1a, is expressed mostly in the freshwater epithelium, while the isoform called Na+/K+ ATPase α1b, is mostly expressed when fish enter saltwater. When salmon migrate from saltwater to freshwater to breed, there is an increase in the amount of mRNA coding for Na+/K+ ATPase α1a in the gill, indicating the shift from ion secretion to ion absorption. Researchers discovered a "mortality-related signature" of gene expression in gills that help identify which fish are successful in reaching spawning grounds and which are not. Fish that were not successful in reaching spawning grounds tended to undergo the transformation from ion-secreting to ion-absorbing epithelium while still living in saltwater. In contrast, fish that successfully reached spawning grounds underwent the gill transformation only when they reached fresh water. It appears that a premature shift in the transformation process may have a detrimental effect on fish's osmoregulation, so they may be in poorer condition by the time they reach fresh water.