9486

• UCREFRP Catalog Number: 9486
• Author: Papoulias, D. and W. L. Minckley
• Title: Food Limited Survival of Larval Razorback Sucker, Xyrauchen texanus, in the laboratory
• USFW Year: 1989
• USFW - Doc Type: Environmental Biology of Fishes
• Copyright Material: YES

76
resulted in a range of 10 to ~- 20 nauplii fish-` at
each of 3 feedings at termination of the experiment
(Table 3). Survivors grew nearly as large as those
receiving -~- 50 nauplii 1-` from the onset of the
experiment (Table 4), indicating that 30 to 60 nau-
plii fish-' d-` was near a minimum required to
survive the critical period.
Discussion
Razorback sucker larvae that were starved, re-
ceived food too late, or were fed an insufficient
quantity usually died between 20 and 30 d after
hatching (Fig. 1, 2). Exact time of yolk absorption
was not recorded in these experiments, but was
estimated at 8 d post-hatch based on observed pres-
ence or absence of yolk in dead larvae and from
Minckley & Gustafson (1982). Larvae persisted
with < 30% losses for 11 d after yolk absorption,
but mortality increased to > 50% after 15 d even
though food was presented (Fig. 1). The critical
period at 18° C, during which larvae must find and
consume suitable food or die, therefore lies be-
tween ~- 8 and 19 d after hatching, and the point of
no return, when starvation is irreversible (Werner
& Blaxter 1980, Powell & Chester 1985), lies be-
tween 19 and 23 d.
Fish larvae utilize energy from foods directly for
growth (Blaxter 1969). Rapid growth may make
them less vulnerable to predation (Cushing 1976)
and environmental hazards, but more dependent
on reliable exogenous foods due to minimal energy
reserves (O'Connell 8r. Raymond 1970, Taylor &
Freeberg 1984). Razorback sucker larvae starved
for different periods, but surviving to take advan-
tage of food when finally offered, grew reasonably
well compared to those fed from d 1. No specific
data are available on sizes at which razorback suck-
ers hatch in Lake Mohave, nor on the efficiency of
yolk utilization, nor rates of growth at ambient
temperatures. Razorback sucker in Lake Mohave
have been observed spawning from early January
through April with hatching occurring from Febru-
ary to May (Langhorst.& Marsh 1986). Temper-
ature of Lake Mohave during the period when the
eggs are incubating tends to be lower than the
incubation temperature for the eggs of the larvae
used in our experiments (9° to 1~° C vs. 21° C).
However, Marsh (1985) found that although razor-
back sucker embryos hatched almost two-thirds as
slowly at 15° as 20° C (5.5 vs. 8.5 d), TL at swim-up
was not significantly different (8.5 vs. 8.4 mm).
Temperature in Lake Mohave during the period
after hatching (15° C-17° C; Langhorst & Marsh
,1986) more closely parallels the temperature in our
experiments (18° C).
Larvae captured from Lake Mohave proper av-
erage 10.6 mm TL, while the largest larva caught
measured 12.2 mm TL (Marsh &Langhorst 1988).
No razorback suckers larger than this have been
caught except for those in the 30--10 year age-class.
Those larvae which have been taken have reduced
Table 3. Experiment 3. Number of food organisms per individu-
al razorback sucker larva at beginning and end of 50 d feeding Table 4. Experiment 3. Total length (TL) ± standard error (SE)
experiments ± standard error (SE). Differing letters in pares- of surviving razorback sucker larvae fed 5, L0, SU, 100, 500, and
theses denote significant differences (p < 0.05) in pairwise com- 1000 nauplii I-'three limes d-'. Differing letters in parentheses
parisons of treatment means. denote significant differences (p <O.US) i n pairwise compari-
sons of treatment means.
Nauplii Nauplii Mean ± SE Range
I-' larva-' nauplii larva-' number of
Nauplii 1-' Number Mean TL
Range
(beginning) (end) nauplii specimens (mm) ± SE TL (mm)
9 16.3 ± 3.2 (x) 9.8- 19.5
5 1 5 4 14.9 ± 0.5 (x) 13.9-15.8
.
10 3.9 17.3 ± 2.0 (x) 13.0- 19.5 10 6 13.6 ± 0.9 (x) 11.8-13.1
50 16.7 21.9 ± 3.3 (x) 16.3- 27.8 50 28 16.1 ± 0.3 (x) 13.7-21.1
100 39.0 49.3 ± 3.6 (y) 43.3- 55.7 100 23 19.4 ~ 0.3 (y) 16.9-23.0
500 195.0 209.5 ± 7.2 (z) 195.0-216.7 500 27 25.0 ± 0.6 (z) 14.9-28.8
lOW 390.0 436.9 ± 28.2 (w) 390.0-487.5 lOW 27 23.7 ± 0.7 (z) 11.5-28.4
8
4
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ai 4
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Frg. 1. Tempe
experiments
sucker larvae
the approxim~
on which eact
Percentage me
or completf
ately empty
In addition
plankton in
larvae have
organisms 1-
unpublished