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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DISCUSSION
Greatest mortality of starved larvae in Experiment 1
occurred between days 20 and 30. Larvae from other experiments
which received food either too late or in insufficient quantity
also died in this time period, presumably of starvation.
Razorback larvae were able to persist without food for as long as
10 days beyond yolk sac absorption with <30% mortality. After 14
days, however, mortalities increased to >50%. A majority of
deaths occurred after food was presented in Experiment 2,
suggesting larvae were too weakened to feed. Thus, the point of
irreversible starvation (Werner and Blaxter, 1980; Powell and
Chester, 1985) was between 17 and 21 days after hatching. A
critical period for these larval fishes (Hjort, 1926), during
which time they must encounter adequate food or die, lies between
yolk sac absorption, and 17 days post-hatch at 180C.
Effect of temperature on duration of this critical period
was not investigated. Experiments (Laurence, 1973; Houde, 1974)
have shown, however, that temperature plays an important role in
time required for incubation, size at hatching, rate of yolk sac
assimilation and rate of yolk sac depletion, so substantial
variation is to be expected under field conditions.
Larvae obviously must encounter food of adequate quality and
in sufficient quantities within a relatively short period of
time. Threshold prey density, beyond which survival differences
were not significant, was 50 nauplii per'liter. The minimum,prey