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<br />Environmental Biology of Frshes l9: 778, 1990.
<br />©194(1 Kluwer Academic Publishers. Printed in the Netherlands.
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<br />Food limited survival of larval razorback sucker, Xyrauchen texanus,
<br />in the laboratory
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<br />Diana Papoulias' & Wendell L. Minckley
<br />Department of Zoology, Arizona State University Tempe, AZ 85287-1501, U.S.A.
<br />t Present address: U.S. Fish -and Wildlife Service, National Fisheries Contaminant Research Center,
<br />4200 New Haven Rd., Columbia, MO 6520.x, U.S.A.
<br />Received 4.1.1989 Accepted 22.8.1989
<br />Key words: Critical period, Starvation, Mortality, Fish larvae, Catostomidae
<br />Synopsis
<br />Razorback suckers in Lake Mohave, -Arizona-Nevada, are suffering recruitment failure. Concomitantly,
<br />lake zooplankton levels are low and variable. We test, under laboratory conditions, the possibility that
<br />starvation is a cause of low recruitment. Razorback sucker larvae that were starved, received food too late, or
<br />were provided with insufficient food died between 20 and 30 d after hatching. Yolk absorption was at ^- 8 d
<br />after hatching, the critical period during which larvae must feed or most will die lies between --- 8 and 19 d,
<br />and the point of irreversible starvation for individuals is between 19 and 23 d after hatching. Results support
<br />food-related mortality as a contributor to year-class failure of razorback sucker in Lake Mohave.
<br />Introduction
<br />Starvation of larvae has long been suggested as a
<br />cause of mortality which may reduce recruitment to
<br />adult populations of fishes (Hjort 1914, 1926, Cush-
<br />ing 1976, Leggett 1986). Larvae are especially vul-
<br />nerable when switching from endogenous (yolk) re-
<br />serves~to exogenous nutrition, termed the `critical
<br />period' by May (1974), when they must encounter
<br />and capture foods sufficient in quality and quantity to
<br />sustain life and promote growth and development.
<br />The razorback sucker, Xyrauchen texanus (Ab-
<br />bott), alarge, endemic species of the Colorado
<br />River basin, western U.S.A., is disappearing due
<br />to chronic year-class failure (Lanigan & Tyus 1988,
<br />Minckley et al. 1990). No recrui`-nent to known
<br />adult populations has been detected for approxi-
<br />mately 30 years, despite extensive sampling with
<br />appropriate gear (McAda & Wydoski 1980, Minck-
<br />ley 1983, Tyus 1987). In Lake Mohave, Arizona-
<br />Nevada, old adults remain common (Minckley
<br />1983, McCarthy &Minckley 1987), and reproduce
<br />every year, but larvae disappear at an average size
<br />of 10.6 mm total length (TL). These wild-caught
<br />larvae have reduced or absorbed yolksacs and their
<br />stomachs are mostly empty. Concomitantly, lake
<br />zooplankton densities tend to be low and variable
<br />(Paulson et al. 1980, Langhorst & Marsh 1986).
<br />Disappearance of larvae may be related to limited
<br />food during a critical period. The three laboratory
<br />experiments reported here were designed to assess
<br />effects of absence, delayed presentation, and varia-
<br />blequantities offood onlarval razorback mortality
<br />and growth during and immediately following the
<br />transition from endogenous to exogenous feeding.
<br />Methods
<br />Experiments were performed at Dexter National
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