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

compressed air from an oil-less air pump. Temperature in the mobile laboratory was
maintained as close to 200e as possible. The photoperiod was maintained at about 12
light: 12 dark.

Live zooplankton were collected every other day either by plankton tow net or light
trap from six sites at Ouray NWR previously shown to have various amounts of selenium in
water and biota, i.e., North Roadside Pond and South Roadside Pond had high
concentrations, Sheppard Bottom pond 5 moderate concentrations, and Sheppard Bottom
ponds 1, 3, and 4 low concentrations (Stephens et al. 1988, 1992). The collection sites were
a beaver pond about 400 yards upstream from North Roadside Pond (NR), South Roadside
Pond (SR), Sheppard Bottom ponds 1 (SI, reference site), 3 (S3), 4 (S4), and 5 (S5) (Figure
3). All six sites were used in studies 1 and 2, whereas study 3 included S 1, NR, and SR,
and study 4 included S3, S4, and S5. Zooplankton were separated by size class using a
standard #40 stainless steel sieve. Plankton passing through the sieve were < 0.425 mm and
were used in the feeding studies. This size of zooplankton was selected because it is the size
equivalent of 24-hour-old nauplii of brine shrimp, which have been readily consumed by
larval razorback sucker in culture activities at the Yankton ERS. After sieving and prior to
counting and feeding, zooplankton were held in reference water.

Zooplankton from each site were concentrated by filtering water through the
collection bucket of a plankton tow net. Organisms were sampled with a 1-ml Hensen-
Stempel pipette and counted with a stereoscope microscope at 0.7x magnification and a
Wards zooplankton counting wheel. The number of organisms in three replicate counts were
averaged and the volume calculated to feed 20 or 40 organisms per fish for the number of
live fish in each exposure vessel.

Larval fish were fed 20 organisms per fish in study 1 for days 1 through 10 and in
study 2 for days 1 through 4. Thereafter, the feeding rate was 40 organisms per fish in
study 1 days 11-25, study 2 days 5-25, and studies 3 and 4 days 1-20. Based on 1600 ml
test water volume and 10 fish per test vessel, the 20 organisms per fish initial feeding rate
was equivalent to 125 organisms/L (200 organisms/1600 ml), and the 40 organisms per fish
initial feeding rate was 250 organisms/L. Fish were fed zooplankton once daily after water
renewal.

Reference water from S 1 used in renewals was collected daily and measured for water
quality characteristics (Table 1). Water temperature and dissolved oxygen concentrations
were measured daily in one replicate of each treatment in each study (Appendix 1). Mean
water temperature was I7.30C in study 1, 17.70C in study 2, I8.2oe in study 3, and I8.90C
in study 4. Mean dissolved oxygen concentrations were 7.6-7.8 mg/L in the studies. Water
quality characteristics were measured weekly in samples collected from the six sites where
zooplankton were collected (Table 2). Conductivity, pH, and salinity were measured weekly
in situ at the six sites where zooplankton were collected (Table 3, Appendix 2). Water
characteristics were measured using standard methods (APHA et al. 1989).

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