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i <br /> <br />ABSTRACT <br />Razorback suckers are disappearing in nature, possibly as a result of <br />food-related mortality of larvae in man-made reservoirs. Effects of <br />absence, delayed presentation, and variable quantities of food on <br />razorback sucker larvae were demonstrated through laboratory and pond <br />experimentation. In laboratory experiments, the majority of larvae <br />died between 20 and 30 d post hatching when no food was presented. <br />Larvae experienced low (<30$) mortality if abundant food was presented <br />at least 19 d post hatching. Mortality was significantly greater for <br />larvae without food 27 (87-%) and 31 d (93%). Razorback suckers fed <br />from 7 d after hatching, but at variable food concentrations, <br />experienced mortality of less than 20% at 50 to 1000 Anemia Salina <br />nauplii/L. Larvae fed rations of 5 and 50 nauplii/L exhibited <br />significantly greater mortality (>70-%); 30 to 60 nauplii/larva/d may <br />be a minimum necessary in the early life stage of razorback sucker. <br />Larvae which did not receive food during the first 31 d after hatching <br />were smallest (15.8 mm TL) and similar in size to larvae fed from 7 d <br />after hatching at concentiations of 5 to 50 nauplii/L. Larvae first <br />presented with sufficient food up to 15 d after hatching grew largest <br />(21.7-23.2 man TL), and comparably to those larvae first fed frcm d 7 <br />at concentrations of 500 and 1000 nauplii/L. Ponds fertilized at <br />three levels resulted in variable mean invertebrate densities of 43.3, <br />23.7 and 12.5 organisms/L, but survival of razorback sucker larvae did <br />not differ among treatments. Total larval biomass and growth were <br />however, greater at the two higher invertebrate densities. <br />Zooplankton densities in Lake Mohave, where larval razorback suckers <br />iii <br />