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FISH IN POLAR OCEANS.
Term Paper ID:24742
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Essay Subject:
Examines conditions conducive for exploitation of cold oceans by fish, adaptations, dangers, growth rates, protein synthesis, migration, genetics.... More...
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8 Pages / 1800 Words
16 sources, 27 Citations,
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Paper Abstract:
Examines conditions conducive for exploitation of cold oceans by fish, adaptations, dangers, growth rates, protein synthesis, migration, genetics.
Paper Introduction:
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
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Nathanailides (11) examined thesignificance of cold-related changes in enzyme activities in fish muscleand found that fish attempt to compensate for these effects by increasingthe activity of aerobic enzymes. Fish inhabiting the colder seas of the polar regions have evolvedmany adaptations that permit them to take advantage of these harshenvironments. Rev. Physiol. Fish. and Physiol. Fish. Am. Can. In cold-adapted species, assembly of tubulin protein toform cytoplasmic microtubules may show a similar response to environmentaltemperatures, with the microtubules of such fish being able to assembleeffectively at low temperatures (3). These authors believed that season effects and evenlatitude may play a role in cold adaptation mechanisms; in support of this,the work of Nelson et al. These authorsexplain their finding of genetic variability in the greater sensitivity oftheir sampling tool--microsatellite (nuclear) DNA as opposed tomitochondrial DNA--which revealed greater levels of allelic variation thanthat reported previously. USA. Evolution of anti- freezeglycoprotein gene from a trypsinogen gene in Antarctic notothenoidfish. Physiol. If migration is not an option for the organism, theproduction of components, either as salts or macromolecules, that candepress freezing points is required. The concentration of solutes in seawater is about 3x that seen inplasma. Aquat. Ice-binding structure and mechanism of ananti-freeze protein from winter flounder. Schurmann, H.; Steffensen, J. 49:516-522; 1992. Can. Fish. Can. Microtubule assembly in cold-adapted organisms:functional properties and structural adaptations of tubulins fromantarctic fishes. Matschak, T.; Stickland, N. J. Fish. In their study of standard metabolic rates inAtlantic cod, Schurmann and Steffensen (15) have suggested that theirunexpectedly low overall SMR values may reflect the impact of otherimportant factors which may influence how ectotherm fish respond to coldsea conditions. Exp. 45:245-26 ; 1983. J. Nature. Aquat. 238:287-295; 1986.11. Unless prevented by some means, ice crystals ininternal water columns can seed additional formation of ice through bodyfluids, with the obvious and expected results of respiratory and systemicorgan collapse and massive tissue destruction (6). J. Davies, P.; Hew, C.; Fletcher, G. The usual strategy is to produce large, colloidal macromolecules,glycopeptides and peptides (4). Differences in exercisephysiology between two Atlantic cod (Gadus morhua) populations fromdifferent environments. Compensation and the expression of adaptation are not alwayspredictable, and high variability seems built into many of the mechanisms,especially at the biochemical level (12). 4. J. 53:4 8-413; 1996.1 . In addition to the relative greater availability of oxygen in coldwater (15), there are rich food supplies, making expansion into theseregions a potentially good strategy at the evolutionary level. J. Fish which routinely inhabit temperate marine oceans haveplasma freezing temperatures between -.5 and -.8 °C, with fish exposed tolower temperatures facing a significant risk of freezing (6). In this study, these two populations were also foundto be genetically distinguishable from cod populations overwintering off-shore along the edge of the Grand Banks continental shelf. Mechanism of temperature acclimation in the carp: amolecular biology approach. In Atlantic cod, several studies have examined the relationship ofchanges at the biochemical or genetic level to migration behavior. Compar. Proc. Sci. Sicheri, F.; Yang, D. Because of this hypertonicity, the freezing temperature of the seacan lower to -1.9° C -- a full degree below the freezing point ofunprotected plasma. J. Theseauthors found that mRNA levels in themselves did not increase, suggestingthat translation or post-transcription rates are primarily the temperature-dependent factor. Migration, often inshore or upstream into bodies of relatively freshwater, is frequently an option used by fish when the water temperaturesaround them lower or change inordinately. Nelson, J.; Tang, Y.; Boutilier, R. J. Inaddition, actual migration behavior in some species may be regulated inpart by the animals' exposure to changes in the temperature of the wateraround them. Studies of the effects of freezing water on the growth of polar fishhave yielded interesting results where protein synthesis is concerned. In someinstances, adult cod tend to remain in water to which they are alreadyacclimated (7), and the movement of individuals into warmer waters is morelikely as a result of the need for food. This study showed that, ingeneral, the smaller the fish, the earlier AFGP appeared in the plasma andthe greater are the quantities of anti-freeze protein built up during thewinter. Yetgene amplification in combination with the potential of high diversityseems also to be the rule, at least at the level of anti-freeze proteins(2), probably enabling a more extensive radiation of ancestral forms intothe nutrient-rich pelagic and related habitats where more modern forms arefound today. J. (14) showed that, in Atlantic cod, a portionof the population in their study remained inshore throughout the winter andthat these fish were different at the genetic level from their off-shoremigrant counterparts. 66:2611-2617;1988. (13) also reported differences in respiratoryphysiology in cod populations inhabiting the same geographical regions butexposed to different environments. Aquat. 67:23 -254; 1994.14. Aquat.Sci. Metabolic rates at both the standardand active levels as well as oxygen consumption are probably impacted byexposure to frigid water (15). J. The mechanismsexamined here not only allow these fish to exploit a rich habitat but alsoenhance their ability to expand their populations even further in the polaroceanic realms. Fish. Different genes areprobably activated at warm and cold temperatures, yielding muscle proteinswhose function will be enhanced during exposure to the appropriatetemperature. As well as producing anti-freeze proteins, most cod exhibit migrationpatterns, moving inshore to summer feeding after spawning offshore andreturning offshore by late autumn and early winter (14). Goddard, S.; Wroblewski, J.; Taggart, C.; Howse, K.; Bailey, W.;Kao, M.; Fletcher, G. Onemight expect muscle power output of a swimming organism to decline withlowered ambient temperature, and there are indications that such a declineis regulated by changes at the genetic level, i.e., at the level of muscleprotein synthesis. Acad. Nathanailides, C. Injuvenile fish, additional compensatory mechanisms at the biochemical levelshave been seen in response to cooling ambient water temperatures. (6) found that, whilesmaller cod tended to be favored over larger individuals based upon theirover-wintering production of AFGP, fish in the very smallest category werethe least freeze-resistant. The influence of temperature on mRNAlevels for muscle contractile protein and a proto-oncogene associated withcell division in Atlantic Salmon (Salmo salar L.). DeVries, A. Aquat. When fish were cold-acclimated, aerobicenzymes increased in content and capillarization was seen, making oxygenand metabolites more easily accessible at the structural level. Sci. Experimental assumptions in themselves have proven to be confoundingvariables in some instances. Different species of fish respond differently at the level ofgrowth of muscle fibres to changes in temperature (12), and interspecificdifferences exist as well in the levels of aerobic enzymes in cold-adaptedfish (1 ). The effective role of AFPs and AFGPs is to lower thefreezing point of an organism's blood plasma without affecting or loweringthe melting point, and to do so without causing osmotic imbalance in thevarious many, sensitive, physiological systems. Sci.53:2333-2336; 1996.12. Aquat. Literature Cited 1. And while cold-adaptation strategies may be very similar among polar fish (1), variabilityexists. Ruzzante, D.; Taggart, C.; Cook, D.; Goddard, S. Zool. Variation within populations has been more difficult to showconclusively. 5. Can. Physiol. Fish that can acclimate to changes in temperature, such as somespecies of carp, are capable of producing different forms of myosin heavychains, i.e., isoforms of the muscle protein and that the expression of theisoform RNA activity is temperature dependent (5). In order tosurvive and thrive in such a habitat, polar fish have evolvedphysiological, biochemical and behavioral compensatory mechanisms tominimize the effects of exposure to the frigid waters. Anti-freeze production, freezeresistance, and overwintering of Juvenile Northern Atlantic Cod (Gadusmorhua). Age, animal length, physiology (as evidenced by not only anti-freeze production but also reproductive state) as well as time of year andprevailing environmental thermal conditions all seem to play a part in cold-adaptive strategies. Biochemical responses to temperaturein the contractile protein complex of striped bass (Morone saxatalis). Sci. Overwintering of adult Northern Atlantic Cod(Gadus morhua) in cold inshore waters as evidenced by plasma anti-freezeglycoprotein levels. Survival of especially hard winters might then favor the youngermembers of the population. L. Can. The most obviousdanger is that of freezing; seawater temperatures in these regions canplunge to -1 to -2 °C. 2. 375(653 ):427-431;1995 (June). Goddard, S.; Kao, M.; Fletcher, G. Fish Biol.5 :1166-118 ; 1997.16. These molecules have been termed anti-freeze polypeptides (AFPs) and anti-freeze glycoproteins (AFGPs) (2).Produced primarily in liver cells, they are subsequently liberated intoplasma and extracellular fluids. Nat. Godard et al. Can. Of molecular weights averaging between2,4 and 34, Daltons, such macromolecules can effectively depress thefreezing point of fish plasma 2 -3 x more than would be expected on thebasis of strict colligative relationships (i.e., not related to adependency on the sheer number of particles added to solution). There may be strong pressure at the gene level to conserve specificaspects of cold-adaptation mechanisms (such as AFP production) with theadded proviso that diverse appearance be the rule. Ruzzante et al. Evidence suggests that fish plasma anti-freezes exert their influenceby altering the structure of water around them as the temperature lowers(4) and binding specificity occurs along specific axes of the anti-freezeprotein in relation to the ice planes (16). Moerland, T.; Sidell, B. Fish. 3. The young of thisspecies (Gadus morhua) can produce relatively greater plasma levels of anti-freeze proteins, and at an earlier point in winter, when compared to thoseseen in adult fish of the same species (6). Phylogenetically distant(unrelated) fishes may synthesize nearly identical forms of anti-freezeproteins, arguing for common ancestry or the existence of extremeevolutionary pressure to conserve a valuable survival strategy (1). 53(3):634-645; 1996.15. Chen, L.; DeVries, A.; Cheng, C. Fish. Biochem. Can. Haakon, H.; Tonn, W.; Welch, H. Many teleost fish found in polar, subpolar andeven cold temperate waters produce macromolecules that, when admitted tothe blood, essentially perform as anti-freeze (4), a mechanism of obviousimportance. The first over-wintering episode may then be a determining factorwith regard to selective pressure, with the individuals successfullyreaching their second winter having the best ability to produce anti-freeze. In addition to the danger of actual freezing, low temperatures canlimit the efficiency of many cellular reactions, among them those thatcontrol oxidative phosphorylation. J. Further, at the level of population dynamics, by extending theamount of time young cod remain at or near their nurseries, thecharacteristics and location of the nursery areas might be moresignificantly imprinted on the young animals. In a study that examined complete energybudgets for Arctic cod (Boreadadus saida) at low temperatures, theseauthors suggest that growth rates in this polar fish mirror that of primaryprey species of copepods, amphipods and capelin that themselves exhibitseasonal patterns, with consumption and respiration rates by the codslowing at lower water temperatures. Effects of temperature, hypoxia andactivity on the metabolism of juvenile Atlantic cod. The 1°difference between environment and plasma fluid is large enough to causefreezing, in part because supercooling of fluids in the presence of icecannot occur. 259:R 237-244; 199 . 51:2834-2842; 1994.8. These mechanisms are found at the cellular, biochemical andbehavioral levels, and some dependence or interraction is likely amongdifferent levels that helps regulate the overall physiology of theseorganisms. Metabolic specialization of muscle duringdevelopment in cold-water and warm water fish species exposed todifferent thermal conditions. This study also stressed theimportance of using a whole-organism approach to the genetic typing of apopulation. Sci. Chemicalreactions in cells are influenced by such factors as temperature,substrates and oxygen delivery; cold adaptation permits polar fish tobypass the usually expected drop in biochemical reaction rates and maintainlife systems when ambient temperatures drop in their habitat. Geneticdifferentiation between inshore and offshore Atlantic Cod (Gadusmorhua) off Newfoundland: microsatellite DNA variation and anti-freeze level. Zool. 94:3811-3816; 1997 (April). These authors proposed that, in order to avoidfreezing, the smallest fish compensated for slightly lowered biochemicalprotection with behavioral tactics, effectively layering behavioralmodifications over the expected physiological response. Nathanailides, C. Detrich, H. Can. Suggestions of little or no gene flow and differentiation indifferent cod populations must therefore be carefully considered, and theuse of multiple assay techniques can more successfully resolve questions ofpopulation structure in species that migrate. Aquat. W. Anti-freeze peptides and glycopeptides in cold-waterfishes. Evidence suggests that migrationpatterns in cold-adapted species may themselves be temperature-regulated atthe genetic levels of these organisms. The low ambient water temperature seen in the oceans of polar regionsprofoundly impacts the marine life which is exposed to it. Gerlach, F.; Turay, L.; Malik, K.; Luda, J.; Scutt, A.;Golspink, G. To combat freezing, polar fish have evolved a variety ofphysiological adaptations. Sci.54:1772-1784; 1997.9. 7. Zool. 53:2147-2155; 1996.13. Further, this sensitivity to temperature has its greatestimpact at the level of mRNA translation, rather than at the level oftranscription of contractile proteins; in embryonic Atlantic salmon, anincrease from 5°C to 8°C or 11°C causes, by hatching time, increasedmyofibrillar protein content at the expense of nuclear proliferation, whencompared to that seen in embryos raised at colder temperatures (9). This mechanism might make seeking overwinteringconditions elsewhere relatively unnecessary by allowing them to acclimatequickly rather than move on. Clearly, marine fish have evolved compensatory strategies to cope inmany ways with the harsher environment of the polar seas, and successfulcold-adaptation is a function of many complex and highly interractivemechanisms. The synthesis of proteins, both at the level of anti-freezemacromolecules and myosin chains, can be temperature-sensitive. Bioenergetics of ArcticCod (Boreagadus saida) at low temperatures. Apparently, cold adaptations are by nomeans predictable, even within species. Fish anti-freeze proteins:physiology and evolutionary biology. J. This in turn could affectsubsequent migration patterns and behavior for these animals. Changes in growth rates of polar fish are also variable, and probablyrelated to cold-adaptation (8). Ann. 6. "Are changes in enzyme activities of fishmuscle during cold acclimation significant?". 118(3):5 1-513; 1997. Sci. Despite the extreme harshness of the environment, there are manyreasons for marine fish to attempt exploitation of polar and sub-polaroceans.
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