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1 <br /> <br />1 <br /> <br />1 <br />1 <br />1 <br /> <br /> <br />1 <br /> <br /> <br />1 <br />1 <br /> <br /> <br /> <br />1 <br />Propagation and Genetics <br />What's Really Happening to Our Stocked Fish? Experiences from the San Juan <br />River <br />Holden, Paul, Mike Golden, Kirk Dahle,1 Manuel Ulibarri2, and Dave Hampton2 <br />B10- WEST, Inc. Logan, Utah; ZDexter National Fish Hatchery and Technology Center, <br />Dexter, New Mexico <br />Approximately 175,000 yoy Colorado pikeminnow were stocked in the San Juan River in <br />New Mexico in early November 2003. About 20,000 of these fish were marked with a <br />calcein mark and held in net pens and netted-off backwaters to study the effect of <br />acclimating the fish prior to release. Approximately 24 hours after stocking, a major <br />mortality event occurred with the fish being held and over the next 48-72 hours 70-80 <br />percent of the fish were lost. Autopsies conducted by Dexter personnel showed that <br />internal organs of the dead fish had hemorrhaged, suggesting the fish could not <br />osmotically adjust to changes in water quality between Dexter water and the San Juan <br />River. It was also hypothesized that the accumulated stress of removal from the rearing <br />ponds, transportation to the San Juan River, and stocking added to the severity of <br />mortality. Dexter had maintained 2,000 of the yoy year class stocked in the river and <br />experiments were designed and implemented in late November to attempt to determine <br />the cause of the mortality and protocols to avoid the mortality in the future. The first set <br />of experiments were conducted at Dexter and used water hauled from the San Juan <br />River. These experiments tested stressed and unstressed fish. No mortalities occurred in <br />these tests. A second set of experiments were conducted in the San Juan River in net <br />pens in a backwater where mortality occurred in early November. This experiment tested <br />various tempering times and attempted to recreate the mortality event. Again, few <br />mortalities occurred. The two sets of experiments suggested that water quality <br />differences by themselves were not the cause of the mortality event, but the combination <br />of accumulated handling stress and water quality differences could not be adequately <br />tested this year. We hypothesize that the accumulated stress of handling from the rearing <br />ponds to stocking, along with a major water quality change, were the causes of the <br />mortality seen in early November 2003. <br />15 <br />