Fish and Cold Water

Despite the extreme harshness of the environment, there are many reasons for marine fish to attempt exploitation of polar and sub-polar oceans. In addition to the relative greater availability of oxygen in cold water (15), there are rich food supplies, making expansion into these regions a potentially good strategy at the evolutionary level. In order to survive and thrive in such a habitat, polar fish have evolved physiological, biochemical and behavioral compensatory mechanisms to minimize the effects of exposure to the frigid waters. The mechanisms examined here not only allow these fish to exploit a rich habitat but also enhance their ability to expand their populations even further in the polar oceanic realms.

The low ambient water temperature seen in the oceans of polar regions profoundly impacts the marine life which is exposed to it. The most obvious danger is that of freezing; seawater temperatures in these regions can plunge to -1 to -2 �C. Unless prevented by some means, ice crystals in internal water columns can seed additional formation of ice through body fluids, with the obvious and expected results of respiratory and systemic organ collapse and massive tissue destruction (6).

To combat freezing, polar fish have evolved a variety of physiological adaptations. Many teleost fish found in polar, subpolar and even cold temperate waters produce macromolecules that, when admitted to the blood, essentially perform as anti-freeze (4), a mechanism of obvious impor

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uclear proliferation, when compared to that seen in embryos raised at colder temperatures (9). These authors found that mRNA levels in themselves did not increase, suggesting that translation or post-transcription rates are primarily the temperature-dependent factor. In cold-adapted species, assembly of tubulin protein to form cytoplasmic microtubules may show a similar response to environmental temperatures, with the microtubules of such fish being able to assemble effectively at low temperatures (3). Migration, often inshore or upstream into bodies of relatively fresh water, is frequently an option used by fish when the water temperatures around them lower or change inordinately. Evidence suggests that migration patterns in cold-adapted species may themselves be temperature-regulated at the genetic levels of these organisms. In Atlantic cod, several studies have examined the relationship of changes at the biochemical or genetic level to migration behavior. In juvenile fish, additional compensatory mechanisms at the biochemical levels have been seen in response to cooling ambient water temperatures. As well as producing anti-freeze proteins, most cod exhibit migration patterns, moving inshore to summer feeding after spawn

Category: Science - F