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I I I I I I I I I I I I I I I I I I I . Temperature Control Water temperature was varied by controlling hot and cold water supplies to each rearing tank as described earlier. Depending on flows needed, desired temperatures from 53-1200 F can be achieved by mixing water from these two lines. In 1991, the FRH had 21 rearing tanks, each receiving 1-1.5 gpm of 68-700 F from this system. Due to mixing of water supplies, it is recommended to have an aeration/nitrogen gas removal system because of the potential for nitrogen gas problems. Note: Upon completion of the Colorado Pikeminnow/Colorado River Squawfish project, the FRH installed a heat exchanger (Maxchanger, Tranter, Inc., Wichita Falls, TX) to reduce energy usage. FISH ESCAPEMENT PRECAUTIONS FOR EFFLUENT WATER All holding facilities were screened (inlet and outlet) to prevent escapement. Screen size was detennined according to fish size. The largest screen size possible without escapement was used in each container to reduce fouling in that container. See rearing container section for specific sizes. BROOD STOCK ACQUISITION Wild Stock During the summer of 1990, ten adult Colorado pikeminnow were captured in the Colorado River near Grand Junction, Colorado and transported to Dexter National Fish Hatchery (DNFH), Dexter, New Mexico. In June of 1991, these 10 wild fish were artificially spawned on-site (DNFH) in an effort to produce genetically diverse half-sibling groups. This was accomplished by subdividing eggs from each fertile female (three total) and fertilizing each group of eggs with milt of each individual male (seven total). This paired mating assured maximum genetic diversity from the ten wild fish (7 x 3 = 21 lots ) and that all fish contributed to the production of offspring. Before spawning took place, each spawner (females and males) was identified by a Passive Integrated Transponder (PIT) tag number (see Marking and Tagging). Along with this PIT number, each fish was labeled with a corresponding letter (female: A, B, or C) or number (male: 1, 2, 3, 4, 5, 6, or 7). When a group of eggs was fertilized, there were a corresponding ill number and ill letter. For example, the eggs from the first female and first male artificially spawned together would be AI, and from that female and the next male would be .A2, etc. (please refer to Table 2. for PIT tag numbers and corresponding labeling of the 1991 FRH year-class.) Care was used to isolate all lots and keep known parentage labels on all fish/egg-rearing containers throughout the 1991-92 study until fish from these known crosses were large enough themselves to be individually PIT -tagged. These advanced fingerlings were then transferred to refugia ponds at Horsethief State Wildlife Area, Grand Junction, Colorado. Captive Stock The focus of the 1989-90 pikeminnow project was to investigate the best intensive culture practices. A domesticated pikeminnow broodstock at Dexter National Fish Hatchery, Dexter, New Mexico provided progeny (fertilized eggs and sac fry) for studies during the 1989-90 study years. 3