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166 largest natural point source in Colorado is in the Glenwood-Dotsero Springs area (Bureau of Rec- lamation, 1983). These springs have a combined flow-rate of 0.5 m3 s -' and a flow weighted av- erage total dissolved solids (TDS) of 15.0 g 1- t (Eisenhauer, 1983) with much of this TDS being due to sodium chloride. The source of salinity for these springs is believed to be from precipitation dissolving evaporites while percolating down to local aquifers (URS, 1982). The United States Bureau of Reclamation (USBR) has devised a plan for diversion of these springs to decrease salinity of the Colorado River. One of the optional uses for this diverted water is aquaculture, with squawfish culture suggested as part of a mitigation package. The purposes of this study, then, were to determine the potential for culture of Colorado squawfish in saline water, to understand more about the effects of salinity on this species, and to provide data useful for risk assessment in cases where development in the basin may increase salinity. Methods and materials Ninety-six hour acute toxicity tests were con- ducted with squawfish using saline water diluted with fresh wellwater to make five dilutions of 0, 25, 50, 75, and 100% (0.5, 5.0, 9.7, 13.7, and 18.3 g 1- t salinity) by volume. Saline water was obtained from Glen-60, a designation assigned by the USBR to a spring located at the Hot Springs Lodge and Pool in Glenwood Springs, Colorado. Freshwater used in the research came from a well located on the Colorado State University cam- pus. Test methods were those in APHA (1980) with water replaced at 48 h to avoid toxicity from metabolic wastes. Tests were repeated three times (ten animals per concentration each time) over a seven month period in 1985-1986. Post-larval Colorado squawfish were obtained from the National Fish Hatchery in Dexter, New Mexico, on 5 August 1985. Fish of this age would correspond to late season age-0 fish in the wild. The fish were produced from broodstock that is maintained at the hatchery. Fish were fed a diet .,r- of appropriately sized trout pellets. Test fish were held at Colorado State University in flow-through facilities receiving the well water supply used as the diluent in toxicity tests. All fish were held in well water two weeks prior to initial toxicity test- ing. Over the seven month period during which fish were tested, mean fish weight increased from 0.410 to 2.607 g. Plastic buckets containing 10-1 of test solution were used as containers during testing. The buck- ets were covered to minimize evaporation and maintain proper salinity. Water temperature was maintained at 22-23 ° C by placing containers in a water bath and dissolved oxygen was main- tained through aeration. Saline water for studies was obtained from Glen-60 in May and December of 1985. After transport back to the laboratory, saline water was stored in several polypropylene and vinyl-lined containers until needed. Concentrations of inor- ganic constituents found in control water and sa- line spring water are shown in Table 1. Due to limited numbers of fish available for testing, survivors from controls and low salinity concentrations of the first two tests were, after six months acclimation in control water, added to other untested fish for use in the third 96 h sur- vival test. Fish were deprived of food for 48 h prior to each test and were not fed during the tests. Measurements of length and weight were conducted on survivors at the completion of each test and on mortalities as they occurred. Death Table 1. Comparison of ions present (mgl-') in control, Glen-60 saline spring water, and equivalent salinity sea water. Parameter Fresh Glen-60 saline Sea wellwater spring water waters Calcium 69 336 210 Magnesium 30 88 667 Sodium 53 6567 5540 Potassium 1 151 190 Carbonate 5 0 - Bicarbonate 248 302 74 Chloride 11 9810 9956 Sulfate 176 1133 1343 Nitrate 18 < 1 - a Data source: Wheaton, 1977.