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ov P 0 u i ns ?,ia ? r <br />FOOD AVAILABILITY AND MORTALITY FOR <br />LARVAL RAZORBACK SUCKER, Xyrauchen texanus <br />by <br />Diana Papoulias <br />Department of Zoology, Arizona State University <br />Tempe, AZ 85287 <br />Starvation of fishes early in life has been suggested as a potential <br />cause of mortality on a significant scale and thus a major factor in reducing <br />recruitment to adult populations. <br />In Lake Mohave, Arizona-Nevada, mean size of captured larval razorback <br />sucker is 10.6 mm total length (TL). Stomachs are mostly empty and lake <br />zooplankton density appears low at the time of razorback hatching. No recruitment` <br />to the adult population has been detected. <br />Laboratory experiments were performed at the United States Fish and <br />Wildlife Service, Dexter, New Mexico facility at water temperatures of 18'*C. <br />To determine when larval razorback sucker must encounter food or die, larvae <br />were started on food at 4-day intervals. Those larvae fed beginning 25 and <br />29 days post-hatch had significantly higher mortalities than those larvae fed <br />5, 9, 13, and 17 days after hatching. The effect of varying food density on <br />mortality was also investigated. Fish receiving 10 nauplii per liter per <br />8-hour period had greater than 70% mortality, while those receiving 50 nauplii <br />per liter per period had less than 30% mortality. Fish which received no food <br />throughout the experiment, as well as those fed at varying time periods or prey <br />densities, experienced peak mortalities between 20 and 30 days post-hatch. The <br />point of irreversible starvation was determined to be between 17 and 21 days post- <br />hatch, and the critical period between 7 and 17 days post-hatch. <br />The results are discussed in relation to observations on razorback sucker <br />larvae in Lake Mohave. <br />"'Tie Council's first Best Student Panne award went to Diana Papoulias for <br />the research described herein. ke Dffer our :sincere con:,,ratulations to <br />Diana `or her excellent ccntri.bu'_ion! <br />@?td 7 ?S?s Cc?vr.C` vo <br />P, 1?a