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60 HAMILTON ET AL or intermittently to 30 /-Lg/L of copper for 56 days postfertilization (30 days pre hatch and 26 days posthatch), whereas survival was reduced at 51 /-Lg/L after 38 days in the intermittent exposure and at 57 /-Lg/L after 63 days in the continuous exposure. How- ever, effects in their study occurred at lower whole-body copper residues (6-10 /-Lg/g) than in our study (23 /-Lg/g and higher). Buckley et al. (1982) also reported reduced growth in coho salmon (Oncorhynchus kisutch) exposed to 70 /-Lg/L of copper for as little as 2 weeks, but no effect on survival even in fish exposed to 140 /-Lg/L for 16 weeks. In contrast, Marr et al. (1996) reported reduced growth in rainbow trout exposed in soft water (hardness 25 mg/L as CaC03) to 4.6 /-Lg/L of copper in 2 weeks, but no apparent effects on survival after 60 days at the highest concentration tested, 9 /-Lg/L. Exposure to zinc concentrations of 79 /-Lg/L in the razorback sucker study (4X) and 130 /-Lg/L in the bonytail study (8X) also could have contributed to reduced growth and survival of fish. Bengtsson (1974b) reported reduced growth in the minnow Phoxinus phox- inus exposed in soft water (hardness 39 mg/L as CaC03) for 30 days to 130 p.g/L of zinc, whereas in a separate experiment with the same species tested in similar water (hardness 47 mg/L as CaC03) survival was reduced at 80 p.g/L (Bengtsson, 1974c). Spehar (1976) reported that female flagfish (Jordanella flori- dae) exposed in soft water (hardness 44 mg/L as CaC03) to zinc had reduced growth at 51 /-Lg/L after 100 days of exposure and reduced survival at 85 /-Lg/L at 30 days. Sinley et al. (1974) reported increased mortality in swim-up rainbow trout exposed in soft water (25 mg/L as CaC03) to 260 /-Lg/L of zinc. Concentrations of copper, selenium, and zinc that cause adverse effects discussed above fall within the range of concentrations tested in the present study, and thus, suggest that they caused the adverse effects ob- served. Copper and zinc are essential inorganics neces- sary to meet the metabolic needs of animals, and are homeostatic ally controlled in fish by metallothionein, a protein found in liver and kidney tissue (Hamilton and Mehrle, 1986). Metallothionein also serves a detoxifica- tion role by sequestering inorganics such as cadmium and mercury, as well as excessive amounts of copper and zinc, and reducing the amount of free metals in tissues, thereby reducing potential toxicity. Selenium is also an essential micronutrient to ani- mals as a component of certain proteins and enzymes where it is selectively incorporated against a concentra- tion gradient of sulfur, which is present at concentra- tions that are orders of magnitude higher than sele- nium concentrations (Stadtman, 1980). However, when selenium is available at greater than micro molar con- centrations, it can be extensively substituted indiscrimi- nately for sulfur in many cellular constituents (Stadt- man, 1974). Although there is a mechanism for the metabolic control of copper and zinc, i.e., metallqth- ionein, there is no known control for selenium. Stadt- man (1974) stated "because of the greater reactivity and lower stability of selenium compounds compared to the corresponding sulfur compounds, the cell may encounter metabolic problems which eventually can lead to death of the organism." The death of fish and wildlife from selenium poisoning has been documented in 12 case histories by Skorupa (1998). The consequence of reductions in total length, weight, or condition factor is that swimming perfor- mance is reduced, and susceptibility to predation is increased (Barns, 1967; Taylor and McPhail, 1985), and feeding efficiency is reduced (Gunn and Noakes, 1987). Functions that promote fish survival are also related to body size (reviewed by Ojanguren et aI., 1996). For example, sensory systems develop rapidly during e"r1y life stages and visual acuity increases with fish siZe, enabling large fish to better detect predators and fqod and resist starvation, thus allowing them access to a wider range of prey, which increases the likelihood of finding appropriate food. Ojanguren et al. (1996) fur- ther stated that better swimming performance by larger fish could reflect the overall fitness because swimming is a highly integrative function requiring muscular strength and coordination, morphometric adequacy, ac- curate sensorial perception, and physiological adjl.\st- ments. It has been hypothesized that interaction of slOw growth and increased early-life mortality have con- tributed to the decline of the endangered Colorado squawfish in the upper Colorado River (Kaeding and Osmundson, 1988). It is also believed that the upper Colorado River provided suboptimal conditions for fish growth because of generally lower water temperatu~es compared to the lower basin. Thompson et a!. (1990 assessed this hypothesis and found that smaller Col- orado squawfish with lower condition factors had ~e- duced survival during overwinter conditions compar~d to larger fish with higher condition factors. Others have also shown that overwinter survival of a variety of otlier fish species depends on fish size and condition factor (reviewed by Thompson et aI., 1991). Overwinter sur- vival of fish has also been shown to be reduced by exposure to selenium at low concentrations in water (4.8 /-Lg/L) and diet (5.1 p.g/g) (Lemly, 1993a). In t~at study, stress from low water temperatures and selenium residues caused hematological changes and gill damage that reduced respiratory capacity, reduced activity and feeding, depleted body lipids by 50-80%, and reduced survival. Consequently, razorback sucker and bony tail with reduced growth may have reduced survival poten- tial. .