Cooperative Fish and Wildlife Research Units Program: Idaho
Education, Research and Technical Assistance for Managing Our Natural Resources

tWe compared the hydrodynamics of replicate experimental mixed cell and replicate standard Burrowspond rearing systems at the Dworshak National Fish Hatchery, ID, in an effort to identify methods forimproved solids removal. We measured and compared the hydraulic residence time, particle removalefficiency, and measures of velocity using several tools. Computational fluid dynamics was used first tocharacterize hydraulics in the proposed retrofit that included removal of the traditional Burrows ponddividing wall and establishment of four counter rotating cells with appropriate drains and inlet water jets.Hydraulic residence time was subsequently established in the four full scale test tanks using measures ofconductivity of a salt tracer introduced into the systems both with and without fish present. Vertical andhorizontal velocities were also measured with acoustic Doppler velocimetry in transects across each ofthe rearing systems. Finally, we introduced ABS sinking beads that simulated fish solids then followed thekinetics of their removal via the drains to establish relative purge rates. The mixed cell raceway providedhigher mean velocities and a more uniform velocity distribution than did the Burrows pond. Vectorsrevealed well-defined, counter-rotating cells in the mixed cell raceway, and were likely contributingfactors in achieving a relatively high particle removal efficiency-88.6% versus 8.0% during the test period.We speculate retrofits of rearing ponds to mixed cell systems will improve both the rearing environmentsfor the fish and solids removal, improving the efficiency and bio-security of fish culture. We recommendfurther testing in hatchery production trials to evaluate fish physiology and growth.