EVALUATION OF EFFLUENT WASTE WATER FROM SALMONID CULTURE AS A POTENTIAL FOOD AND WATER SUPPLY FOR CULTURING LARVAL PACIFIC LAMPREY Entosphenus tridentatus

Pacific lamprey populations have declined in abundance from historic levels in the U.S. Pacific Northwest. The decline of this species has raised concern among tribal, state and federal management agencies. Conservation efforts involving this native species include habitat restoration, improvements to fish passage systems, and development of culture techniques. The present research focused on refining the culture methods for the larval stage of the species. The first objective of this study was to test the viability of waste water from salmonid culture as a potential food source and water supply for raising the ammocoete (larval) stage of the Pacific lamprey. Larval lamprey filter feed on detritus and cohabitate with juvenile salmonids in the wild, therefore the effluent water from rearing salmonids may be a viable source of water and food for culturing lamprey. Rearing lamprey in this manner could be a sustainable method for raising lamprey at existing salmonid hatcheries. The second objective was to determine if the quality of the effluent water is improved by running through lamprey culture tanks before it leaves the facility. Release of nutrients in effluent water could have negative impacts on wild systems, and the filter feeding action of the lamprey may sequester nutrients from the water thus improving the quality of the effluent stream.

The experimental unit in this study was a combination of a steelhead trout (Onchorynchus mykiss) tank containing 150 juveniles and a lamprey tank containing 90 fish. Flow through well water entered the steelhead tank and then flowed into the lamprey tank for a second use. To complete the first objective, three treatments with three experimental units each tested the use of the effluent, a conventional lamprey diet, or both combined as a means for rearing lamprey. For the second objective a fourth treatment with three replicate systems where lamprey were excluded served as a control to test the effect of lamprey presence on effluent quality. After nine weeks of study, growth, survival, proximate composition and fatty acid profile of the remaining lamprey were assessed. The quality of the effluent water as it left the lamprey tanks was also analyzed. The results of this research may provide additional methods for producing quality lamprey and to potentially reduce effluent concerns from salmonid aquaculture.