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a 3.8-L plastic jar filled with site water, covered, and transported to the laboratory in coolers. In the laboratory, the samples were thoroughly mixed and a subsample was collected in a glass vial and preserved in 70% ethanol. The subsample was used to make semi-quantitative estimates of species composition at each station. Sediment grab samples for separation of benthic invertebrates were collected in plastic jars and transported in coolers to the laboratory. Sediment samples were washed through a set of sieves and the invertebrates extracted from the debris using stainless steel forceps. Generally, two sets of aquatic invertebrate samples were collected from each sample station on a monthly basis when available, placed in Whirl-Pak bags, and stored frozen at -20oC. One set was analyzed for selenium concentrations by atomic absorption spectrophotometry, and the other set was analyzed for concentrations of inorganic elements by inductively coupled argon plasma (ICP) spectroscopy analysis. One sample from two different lots of the commercial diet fed to adults at the Horsethief reference site also was collected for selenium analysis. Spawning In late spring of 1996 after water temperature rose to 160C (-600F) and remained there for about a week (last week of April), fish held at Adobe Creek and North Pond were captured by personnel of the CRFP between April 24 and 29 using trap (fyke) nets and electrofishing methods and transported to the fish holding building at Horsethief. Adults held in earthen ponds at Horsethief were collected using a seine. All fish were held in 1.3 m-diameter tanks in the holding building supplied with flowing Colorado River water supplemented with oxygen delivered through diffuser bars. Muscle plugs were taken from all fish for selenium analysis. Muscle plugs also were taken from 14 hatchery brood stock fish held at Horsethief. To induce spawning, fish were injected with human chorionic gonadotropin hormone on each of 3 consecutive days, beginning 5 days prior to spawning date. Fish were not injected on the fourth day, and were spawned on the fifth day. All females were injected at the rate of 220 International Units (IV) per kg of body weight. All males were injected at the rate of 660 IV per kg one time, 5 days prior to spawning. After inspection for spawning characteristics (i.e., tubercles present and milt running in males, coloration, plumpness of females), as many adults as possible were spawned. Eggs from each female were fertilized with sperm from at least one male. Fertilized eggs were washed in bentonite clay solution to reduce adhesiveness and then were water hardened in Colorado River water. Eggs were transported to 24-Road Fish Hatchery (hereafter termed 24-Road), Grand Junction, CO, and placed in incubation buckets with screened bottoms. Eggs from each female spawned were held in separate buckets. Buckets were held in 1.3 m-diameter tanks with recirculated 24-Road Fish Hatchery water (hereafter termed 24-Road water). Two samples of eggs from each spawn were collected, placed in Whirl-Pak bags, and stored frozen at -20oC until thawed for selenium and ICP analyses. After spawning, two fish from each site were sacrificed (euthanized with MS-222 [tricaine methanesulfonate]) to determine selenium concentrations in various tissues. Sacrificed fish were stored at -20oC until thawed for selenium analysis. After spawning, adult fish from Adobe Creek and North Pond, along with Horsethief and brood stock fish, were held in the same earthen ponds at Horsethief for 60 days to determine the rate of selenium depuration from their tissues. Fish were captured at 30 and 60 days post spawning, identified by their PIT tag, measured for total length and weight, inspected for general 17 I I I I I I I I I I I I I I I I I I I