7701 - Laserfiche WebLink

Home Browse Search

~. 167 was defined as lack of opercular movement. Le- thal concentrations to 50 percent of the test fish (LC50) were estimated by the trimmed Spearman Karber method (Hamilton et al., 1977). Temper- ature (glass thermometer), dissolved oxygen (Y.S.I. model 57 meter), salinity (Y.S.I. mode133 meter), conductivity (Y.S.I. model 33 meter), pH (glass electrode), and ammonia (ion specific elec- trode) were measured daily during tests. Results and discussion Colorado squawfish directly transferred to 100% Glen-60 water, died within 6 h. Squawfish all sur- vived at 9.7 g 1-'salinity and LCso's for the three tests ranged from 11.8 to 14.7 g 1-' salinity at 96 h. Since confidence intervals for the three rep- licates overlapped, these data were combined and the LCSd was estimated to be 13.1 g 1-' salinity (95% confidence intervals 12.4-13.8). Water quality conditions measured during testing were satisfactory for the well-being of the fish (Table 2). While toxicity tests on Glen-60 water were being conducted, a separate test on squawfish acclimation to high salinities was also performed. Results, however, were inconclusive due to high mortality of control fish. It is possible that food deprivation during initial acclimation (one week) and the 96 h testing that followed was the cause of increased mortality in these relatively small fish (0.74 g average weight). When fish were offered food midway through the acclimation period, fish in control water fed while those exposed to di- luted Glen-60 water (8.5 g 1-' salinity) did not. This observation suggests that acclimation of squawfish to saline water may need to be initiated at some lower salinity. Glen-60 is asodium-chloride dominated water and is similar, in many respects to sea water (Ta- ble 1). LCso's of other primary freshwater fishes (Ictalurus punctatus and Micropterus salmoides) tested in Glen-60 water were similar or slightly higher than literature values (Nelson, unpublished data) suggesting that Glen-60 water is similar to seawater in this regard. While salinity tolerance"is of interest to biolo- gists when studying fish distributions and habitat requirements, little material has been published dealing with effects of salinity on Colorado squawfish. In a related paper Pimentel & Bulkley (1983) reported TDS concentrations that were preferred or avoided by a variety of Colorado River fishes including Colorado squawfish. In their study, chloride was kept relatively constant while other ions were increased across the dilu- tion gradient, so squawfish salinity tolerance can- not be inferred from this work. Salinity tolerance of Colorado squawfish might be expected to be similar to that found in other primary freshwater fishes. This appears to be true when tolerances of fishes in the same Family (Cyprinidae) are examined. According to a toler- ance ranking by the United States Environmen- tal Protection Agency (EPA, 1988), goldfish (Carassius auratus), and fathead minnow, (Pimephales promelas) have '96 hr LCSO's of 16.1 and 11.9 g 1-'salinity, respectively (based on the formula, Salinity (g 1-') = 0.03 + 1.805 x Chlo- rinity (g I -' );Wheaton,1977). These data bracket Table 2. Ranges of physical and chemical parameters observed during salinity testing of Colorado squawfish. Parameters Concentration of Glen-60 (% by volume) 100 75 50 25 0a Dissolved Oxygen (mg L- i) 6.3-6.7 6.6-7.1 6.6-7.3 6.8-7.5 7.0-7.8 pH 8.3-8.5 8.3-8.6 8.3-8.6 8.2-8.6 8.1-8.4 TANb (mg 1-1) 0.042-0.74 0.036-1.6 0.066-1.0 0.046-0.94 0.036-0.80 a Fresh wellwater. b TAN =total ammonia-nitrogen.