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Title: Comparing the effects of feeding a grain- or a fish meal-based diet on water quality, waste production, and rainbow trout Oncorhynchus mykiss performance within low exchange water recirculating aquaculture systems

Author
item DAVIDSON, JOHN - Freshwater Institute
item GOOD, CHRISTOPHER - Freshwater Institute
item Barrows, Frederic
item WELSH, CARLA - Freshwater Institute
item KENNEY, P - Freshwater Institute
item SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2012
Publication Date: 9/3/2012
Citation: Davidson, J., Good, C., Barrows, F., Welsh, C., Kenney, P.B., Summerfelt, S.T. 2012. Comparing the effects of feeding a grain- or a fish meal-based diet on water quality, waste production, and rainbow trout Oncorhynchus mykiss performance within low exchange water recirculating aquaculture systems. Aquacultural Engineering. 52:45-57.

Interpretive Summary: Traditionally, fish meal harvested from the wild (i.e. sardines, anchovies) has been a primary protein source in the feeds of farmed fish. Fish farming has grown to the point that alternatives to fish meal must be found. The development of fish meal free feeds has been a research priority around the world and several effective diets have been developed. The effect of the diet on fish performance and on the rearing environment was investigated, and while good growth was observed when feeding the grain based diets, the formulation still needs further refinement to be optimal in recirculation water systems.

Technical Abstract: Feeding a fish meal-free grain-based diet (GB) was compared to feeding a fish meal-based diet (FM) relative to water quality criteria, waste production, water treatment process performance, and rainbow trout Oncorhynchus mykiss performance within six replicated water recirculating aquaculture systems (WRAS) operated at low exchange (0.26% of the total recycle flow; system hydraulic retention time = 6.7 days). Rainbow trout (214 ± 3 g to begin) were fed the GB diet within three WRAS and the FM diet within the other three WRAS for three months. Feeding the GB diet resulted in significantly greater total ammonia nitrogen (TAN) throughout the study, as well as significantly greater total suspended solids (TSS) and carbonaceous biochemical oxygen demand (BOD) over the greater part of the study. Greater counts of fine solids (2-30 µm) were associated with the GB diet. Despite greater concentrations of TSS and BOD, water clarity was improved for the GB diet as reflected by significantly reduced true color and increased ultraviolet transmittance. Total and dissolved phosphorous, as well as the daily mass captured per kg feed of total phosphorous were significantly lower within the effluent associated with the GB diet. The daily mass of total nitrogen and TSS captured per kg feed and discharged from each WRAS was equal between diets, but waste load among three discharge flows varied. Waste removal efficiency across unit processes was similar between diets, with the exception of solids removal efficiency across the microscreen drum filter and the radial flow settler, which was generally lower for the GB diet. Rainbow trout growth, feed conversion, condition factor, and survival were similar between diets. Survival was near 99.5 ± 0.2% for both diet treatments. Skin-on fillet yield and whole-body protein levels were significantly greater at the end of the study for trout fed the GB diet. Omega-3 fatty acid concentrations were similar within the fillets of fish fed each diet, but the fillets of fish fed the GB diet contained significantly greater levels of Omega-6 fatty acids. Overall, the GB diet evaluated during the present study proved to be a viable feed option for use within a low exchange WRAS. However, further refinements to grain-based diet formulations that lead to improved water quality in WRAS are still necessary.