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Post-Treatment Monitoring

Fish Health – Growth Rate, Survivability, and Condition (K) Factor

The health of stocked rainbow trout is yet another testament to the amazing recovery of Diamond Lake. The growth rate of trout was phenomenal for 2007 and 2008 – fingerlings stocked in mid-June reached 11 inches by October.

Leading up to the Sept. 2006 rotenone treatment, both the growth rate of legal-sized trout and survival rate of stocked fingerlings was nearly zero. The estimated 95 million tui chub in Diamond Lake effectively out-competed trout for zooplankton and benthic invertebrate food sources. With a lake now free of tui chub, stocked fingerling trout grew an average of nearly two inches per month during the summers of 2007 and 2008.

To create a fish health index, biologists weigh and measure fish from snout to the fork in their tail fin. The Condition Factor (k) is a relationship between the fork length in centimeters and weight in grams of the fish where K=(100(W)) / (L^3)

See a graph of historic fish health (pdf) at Diamond Lake.

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ODFW employees pull a trap net on Oct. 31, 2007. Trout stocked earlier in the summer as fingerlings were measured and weighed to calculate fish condition. Trout over 14 inches were released. ODFW employee releases a healthy 16-inch rainbow trout during the trap netting operation.
100,000 fingerlings were stocked in Diamond Lake on June 12, 2007

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