Acclimation of Osmoregulatory Function in Salmon

Summary

Acclimation of Osmoregulatory Function in Salmon Download a printable version of this essay. As you know, salmon spend most of their life in the open ocean, where they reach sexual maturity, but lay their eggs gravel beds at the upper reaches of (freshwater) streams. When the eggs hatch, the young salmon spend several months migrating downstream to the ocean where they remain for some 3-5 years. When mature, the adult salmon return to mouth of stream where they hatched (they remember the taste/smell of the water in the stream), migrate upstream to its headwaters, spawn, and die. As you might expect, there are some serious physiological challenges presented by habitats as different as freshwater streams and the open ocean. The purpose of this essay is to discuss one of those challenges — how to keep the concentration and composition of their body fluids within homeostatic limits while migrating from fresh to salt water and back again — that salmon must cope with during their life cycle. Osmoregulatory Problems for the Salmon The information you need to know in order to understand salmon osmoregulation is presented in the following table. Salmon Body Fluids Ocean Water Fresh Water Total Solute Concentration 1.0% 3.5% < 0.1% % NaCl 50% (approx.) > 99% n/a Like nearly all vertebrates, the salmon is an excellent osmoregulator. However, like virtually all osmoregulators, the salmon is never in true equilibrium with its surroundings. As you can see from Row #1 in the accompanying table, in the ocean, the salmon is bathed in a fluid that is roughly three times as concentrated as its body fluids, meaning that it will tend to lose water to its surroundings all of the time. And, because the composition of its body fluids is so different from the ocean water, the salmon will be faced with all manner of gradients that are driving exchanges that will continuously tend to drive its body fluids' concentration and composition beyond homeostatic limits. In particular, the very high c...