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

pendent
lenergy
aylor &
starved
advan-
sonably
specific
cksuck-
iency of
ambient
Mohave
January
t Febru-
'emper-
hen the
han the
larvae
21° c).
h razor-
hirds as
wim-up
.4 mm).
period
Marsh
~e in our
>'per av-
caught
,t 1988).
ve been
;e-class.
reduced
error (SE)
,SOO,and
rentheses
compari-
ange
L (mm)
'~.9-15.8
.8-13.7
~.7-21.1
~.9-23.0
.9-28.8
.5-28.4
8
4
0
4
2
0
8
~ 4
'0 0
4
0
E2
w
0 0
a~ 4
E2
z 0
2
0
2
2
Fig. 1. Temporal distribution of mortalities in delayed feeding
experiments (B-H) compared with that of starved razorback
sucker larvae (A). The continuous vertical line at d 8 indicates
the approximate time of yolk absorption; arrows indicate days
on which each set of larvae (B-H) were first provided [ood.
Percentage mortality is in the upper right corner.
or completely-absorbed yolksacs, and predomin-
ately empty stomachs (Marsh &Langhorst 1988).
In addition, reported averas~ densities of zoo-
plankton in areas of Lake Mohave proper where
larvae have been captured vary from 1.5 to 26.3
organisms I-' (Marsh &Langhorst 1988, Paulson
unpublished data). Furthermore, only a portion of
~~
8 STARVATION
4
0 A
~
~; 2 100/L
20%
p O B
i
~ 50/L
~ 2 18.3%
o
L 0 ~
a~
~ 4 10/L
~ 2
Z 73.3%

0 0
8 5/L
4 es.7%
0 E
0 5 10 15 20 25 30 35 40 45 50
Days post-hatching
Fig. 2. Temporal distributions of mortalities in variable-ration
experiments (B-E) compared with that of starved razorback
sucker larvae (A). The continuous vertical line at d 8 indicates
the approximate time of yolk absorption; treatment ration and
percentage mortality are in the upper right corner. Mortalities
for rations of 500 and 1000 nauplii I-' are not presented since no
dead fish were recovered.
this zooplankton biomass is presumably available
to the larvae. Marsh &Langhorst (1988) reported
that the preferred foods of razorback larvae in
Lake Mohave were cladocerans and that these
comprised nearly 64% of total zooplankton densi-
ty.
Our results suggest that wild-caught larvae from
Lake Mohave are in transition from dependence on
endogenous to exogenous foods, and therefore in
the critical period. In our experiments, starvation
killed most 20-30 d old larvae. Experimental larvae
at death measured only slightly less (9.3-10.1 mm
TL) than the average wild-caught larva (10.6 mm
TL) as estimated by Marsh &Langhorst (1988), at
most, a few weeks old. However, some ~urvae in
our 50 d experiments that had received asub-opti-
mal ration of brine shrimp were nearly half the size
of those receiving excess nauplii indicating that age
may not be reliably predicted from size when food
U 5 1 U 1 5 LU l5 .SU S5 4U 45 5U
Days post-hatching