9691

• UCREFRP Catalog Number: 9691
• Author: Recovery Implementation Program.
• Title: Recovery Implementation Program For Endangered Fish Species in the Upper Colorado River Basin 25th Annual Recovery Program Researchers Meeting.
• USFW Year: 2004.
• USFW - Doc Type: Moab, UT.
• Copyright Material: NO

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Propagation and Genetics

What's Really Happening to Our Stocked Fish? Experiences from the San Juan
River

Holden, Paull, Mike Golden I, Kirk Dahle, I Manuel Ulibarre, and Dave Hampton2

I BID-WEST. Inc. Logan, Utah; 2Dexter National Fish Hatchery and Technology Center,
Dexter, New Mexico

Approximately 175,000 yoy Colorado pikeminnow were stocked in the San Juan River in
New Mexico in early November 2003. About 20,000 of these fish were marked with a
calcein mark and held in net pens and netted-off backwaters to study the effect of
acclimating the fish prior to release. Approximately 24 hours after stocking, a major
mortality event occurred with the fish being held and over the next 48-72 hours 70-80
percent of the fish were lost. Autopsies conducted by Dexter personnel showed that
internal organs of the dead fish had hemorrhaged, suggesting the fish could not
osmotically adjust to changes in water quality between Dexter water and the San Juan
River. It was also hypothesized that the accumulated stress of removal from the rearing
ponds, transportation to the San Juan River, and stocking added to the severity of
mortality. Dexter had maintained 2,000 of the yoy year class stocked in the river and
experiments were designed and implemented in late November to attempt to determine
the cause of the mortality and protocols to avoid the mortality in the future. The first set
of experiments were conducted at Dexter and used water hauled from the San Juan
River. These experiments tested stressed and unstressed fish. No mortalities occurred in
these tests. A second set of experiments were conducted in the San Juan River in net
pens in a backwater where mortality occurred in early November. Tliis experiment tested
various tempering times and attempted to recreate the mortality event. Again, few
mortalities occurred. The two sets of experiments suggested that water quality
differences by themselves were not the cause of the mortality event, but the combination
of accumulated handling stress and water quality differences could not be adequately
tested this year. We hypothesize that the accumulated stress of handling from the rearing
ponds to stocking, along with a major water quality change, were the causes of the
mortality seen in early November 2003.

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