7269

• UCREFRP Catalog Number: 7269
• Author: Pimentel, R. and R. V. Bulkley
• Title: Concentrations of Total Dissolved Solids Preferred or Avoided by Endangered Colorado River Fishes
• USFW Year: 1983
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

596 PIMENTEL AND BULKLEY
TABLE 1.-Initial concentrations (mgIliter)a of the major ions in each compartment of the experimental chamber used
to establish preferences and avoidances of total dissolved solids (TDS) for Colorado River fish.
Compartment number
Ion 1b 21 3 4 5 6 7 8
Ca- 47 160 160 160 160 160 160 160
Mg" 16 82 170 250 330 420 500 580
Na` 1.0 170 360 550 750 930 1,100 1,300
K+ 0.0 6 6 6 6 6 6 6
Cl- 4.0 220 220 220 220 220 220 220
SOq 6.2 590 1,300 2,000 2,800 3,500 4,200 4,900
HCO,- 200 210 210 210 210 210 210 210
Total 274 1,438 2,426 3,396 4,476 5,446 6,396 7,376
Conductivity in pmhos/cm = 618 + 0.68 mg/liter TDS; r2 = 0.91.
b Logan City water.
Approximate mean composition of Colorado River water at Moab, Utah (USGS 1978)
Methods
Preliminary experiments with humpback
chubs indicated that larger fish were less sen-
sitive to high TDS concentrations than were
smaller fish. For this reason, as well as the larger
sample size permitted by smaller fish, juvenile
fish for all three species were used in the ex-
periments. Fish were hatched and reared at the
Willow Beach (Arizona) National Fish Hatch-
ery. Colorado squawfish were hatched in July
1980 and bonytails and humpback chubs in May
1981. Fish were held outdoors in concrete race-
ways and fed commercial pelleted trout feed
until they were transported to the Utah Water
Research Laboratory. There they were held in
224-liter circular fiberglass tanks with a 14-hour-
light, 10-hour-dark photoperiod. The water
supply was dechlorinated Logan City water (Ta-
ble 1). Dissolved oxygen remained between 90
and 100% of saturation, pH between 7.6 and
8.2, and total ammonia below 0.2 mg/liter. The
fish were fed commercial trout feed ad libitum
twice daily and were acclimated to 14 C (range,
+I C) by the procedures of Richards et al.
(1977). Fish used in the tests were 2.5 to 5.0 cm
long and were either young of the year (bony-
tails and humpback chubs) or yearlings (Colo-
rado squawfish).
Preference for and avoidance of various con-
centrations of TDS were tested in an enlarged
version of a salinity-gradient device designed by
Staaland (1969) and modified by Reynolds and
Thomson (1974). The device was a long trough
(243 cm long, 45 cm wide, 30 cm deep) with a
series of staggered partitions 20 cm high (Fig.
1) that formed eight compartments. The ap-
paratus was filled by placing a sealed plexiglass
lid on top, tilting the trough on one end, and
pouring water of decreasing salinity successively
into each of the eight compartments. As the
box was filled, it was lowered to a horizontal
position. The partitions maintained disconti-
nuity layers created during filling. Compart-
ment 1 contained dechlorinated Logan City
water to which the fish were acclimated; com-
partment 2 contained the major ions found in
the Colorado River at Moab, Utah (USGS 1978;
mean of 1978 water year, April-July excluded).
Compartments 3-8 contained the same ions as
compartment 2 except that concentrations of
Mg++, Na', and S04- were raised a combined
total of 1 g/liter per compartment in sequence
(Table 1). These three ions are the major con-
TOP VIEW
AlRSTO? PARTITIONS FILLING
SIDE VIEW /HOLE
8_?/ 6 5 4\ ? 2 1
WATER DENSITY
LEVEL INTERFACE
FIGURE 1.-The total-dissolved-solids (TDS) gradient de-
vice modeled after Staaland (1969) and Reynolds and
Thomson (1974). The length is 243 cm, width 45 cm,
height 30 on. The density interface is where water of
lesser IDS concentration floats on top of water of greater
IDS concentration.
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