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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />32 <br /> <br />line C. However, because that it is highly probable that <br /> <br />food is available and that age-O fish feed during winter, <br /> <br />line C would be accurate only if the maintenance <br /> <br />requirements of these wild fish were so great that, despite <br /> <br />overwinter feeding, wild fish depleted their energy reserves <br /> <br />faster than starved aquarium-held fish. <br /> <br />If wild fish were able to ingest sufficient calories to <br /> <br />more than offset their higher metabolic demands, the <br /> <br />resulting size versus survival relationship would fall <br /> <br />somewhere between lines A and B. Such a situation could be <br /> <br />illustrated by curve D, which would be non-linear because as <br /> <br />fish size increases, the availability of suitably-sized prey <br /> <br />items also increases. The probable key size for age-O <br /> <br />Colorado squawfish is the size at which they are able to <br /> <br />shift to a piscivorous diet, which seems to occur at 30-50 <br /> <br />mm TL (USFWS, unpublished data). Along the lower portion of <br /> <br />curve D, smaller fish are gradually able to feed on a wider <br /> <br />range of invertebrate food organisms, which results in small <br /> <br />increases in both fish size and time to starvation (but <br /> <br />slope D > slope A or C). Then, at some critical size (i.e., <br /> <br />50 mm), the fish are capable of switching over to a diet <br /> <br />consisting mainly of fish. This conversion to a more <br /> <br />energetically profitable prey results in significant <br /> <br />increases in time to starvation for those fish larger than <br /> <br />the critical size (where slope D < slope A or C). This <br /> <br />"piscivory size threshold" is undoubtedly a range rather <br />