3301

• UCREFRP Catalog Number: 3301
• Author: Papoulias, D.
• Title: Effect of Food Availability on Growth and Mortality of Larval Razorback Sucker,
• USFW Year: n.d.
• Copyright Material: NO

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smaller at death than when stocked. Fists which died from
insufficient food were approximately the same size at death as
when stocked, indicatin4 a small amount of growth before
starvation.
Growth at the stage when fish depend on endogenous food and
switch to exogenous food is related to temperature and its effect
on yolk sac efficiency. It may therefore be difficult to predict
size at which fish from different temperature environments will
die due to insufficient food during the critical period. Lake
Mohave, for example, is colder (11-150C) during the period of
incubation and hatching for razorback sucker. We may expect
larvae to be larger at hatching with a reduced yolk sac yet able
to survive with inadequate food for a longer period (Houde,
1974). Marsh (1985), found that razorback sucker hatched almost
twice more slowly at 150C as at 20oC; however, total length of
larvae at swim-up was not significantly different at the two
temperatures. No information is available on size at which
razorback hatch in Mohave nor efficiency of yolk utilization at
the ambient temperature. Lake Mohave larvae which have been
examined had reduced or recently absorbed yolk sacs and 67% of
stomachs empty (Langhorst and Marsh, 1986). Of fish with food
about 70% had <10 food items - cladocerans, copepods or rotifers-
and the average is 4 items (Marsh, unpubl. data). Density of
zooplankton in Lake Mohave during the first 4 months of the year
is <5 organisms/L (Paulson, pers. comm.). Langhorst and Marsh
(1986), reported zooplankton prey items at an average of 1.5/L