7821

• UCREFRP Catalog Number: 7821
• Author: Hamilton, S. J., et al.
• Title: Evaluation Of Toxicity To Larval Razorback Sucker Of Selenium-Laden Food Organisms From Ouray NWR On The Green River, Utah.
• USFW Year: 1996.
• USFW - Doc Type: \
• Copyright Material: NO

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Supplemental feeding study

Survival at the end of the 20-day exposures was 95-97 % in the test with 5-day old
larvae, 90-95% in the test with lO-day old larvae, and 97-100% in the test with 24-day old
larvae (Table 12). There were no significant differences in survival between feeding groups
or between age groups.

For all age groups, fish length and weight were significantly different between feeding
groups (Table 12). Larvae fed 80 organisms/fish were significantly larger than larvae fed
either 20 or 40 organisms/fish, and larvae fed 40 organisms/fish were significantly larger
larvae fed 20 organisms/fish.

DISCUSSION

Survival and growth

Mortality in study 1 did not occur until day 5 of feeding selenium-laden zooplankton
when fish age was 10 days posthatch. This mortality was similar to study 2 where mortality
occurred earlier at day 2 of feeding when fish were 12 days posthatch. Mortality in studies 3
and 4 occurred later than in studies 1 and 2 probably because of the advanced life stage (24-
28 day old) larvae at test initiation. In all four studies, about 50% mortality occurred
consistently after 10 to 15 days exposure in all treatments (study 1 10-15 days; study 2 6-12
days; study 3 13-15 days; study 4 14-16 days) (Figures 4-7, Appendices 3-6). In contrast,
fish age when 50% mortality occurred was 15-20 days posthatch in study 1, 16-22 days in
study 2, 37-39 days in study 3, and 42-44 days in study 4. Mortality in this study occurred
sooner than reported by Papoulias and Minckley (1990) who found the median time to 50 %
mortality in starved larval razorback sucker was 24-25 days posthatch. They also reported
that larval razorback sucker first fed food beginning 7 days posthatch had 100 % survival and
those beginning 11 or 15 days posthatch had 90% survival after 50 days posthatch.
Starvation was probably not a cause of the reduced survival in the present study because
larvae were fed prior to and during the studies and mortality occurred in a shorter time
period than observed by Papoulias and Minckley (1990) for starved fish.

A concentration response between survival and selenium or other inorganic
concentrations in zooplankton was not observed in this study because a threshold for toxic
stress was apparently reached rapidly and exceeded in the larval razorback sucker, including
those in the reference treatment. Consequently, larvae in all treatments died at about the
same time. In study 1, the median time to death of larvae fed zooplankton from SR and NR
was significantly longer than for larvae fed zooplankton from S 1, which suggests an
antagonistic interaction between inorganics present in the food organisms. This reduced or
delayed stress in the SR and NR treatments, in turn, caused a significant delay in mortality
compared to the S 1 treatment. If a typical concentration response was present, larvae fed
zooplankton from SR and NR should have died first because inorganic concentrations were
highest in SR and NR. However. because mortality was significantly delayed in the SR and

40