7277

• UCREFRP Catalog Number: 7277
• Author: Papoulias, D.
• Title: Survival and Growth of Larval Razorback Sucker,
• USFW Year: 1988.
• Copyright Material: NO

Consistent failure of razorback sucker year classes in Lake
Mohave, Arizona-Nevada, is not entirely understood. Th date, egg and
larval predation by non-native fishes has been considered the most
likely explanation. Alternatively, in marine systems, insufficient
amounts or qualities of foods, especially during the transition from
Yolk to exogenous feeding, is often identified as a major cause of
mortality of larval fishes. Rearing of razorback sucker larvae in
ponds fertilized at three levels, "high", Ismedium", and "low", with
mean invertebrate densities of 43.3, 23.7 and 12.5 o ;anisms/L
respectively, did not result in significant differences in survival of
razorback sucker (77.0, 89.8, and 67.4-1, respectively). However,
total larval biomass and growth were greater at the two higher
invertebrate densities. Razorback sucker larvae may successfully
survive a reduced food source through increased search effort at the
cost of growing more slowly. Volume of food in guts, but not mmibers
of food organisms, increased linearly with growth of larvae. Numbers
and volumes of food items did not differ relative to fertilization
treatment. First foods of larval razorbacks were diatoms, detritus
and algae. Soon, small rotifers and chircn raids were taken. As
larvae grew, larger organic, primarily cladocexans, were selected.
Based on larval survival relative to zocplankton standing crops
in Ponds, year-class failure of Lake Mohave razorback sucker may well
be attributable to nutritional deficiency at the lowest recorded
densities of reservoir zocplanktcn. However, starvation or food-
related problems do not seem likely explanations at the higher
zooplankton densities in Lake Mohave.