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

Authors: DAVIDSON III, JOHN - Freshwater Institute; GOOD, CHRISTOPHER - Freshwater Institute; Barrows, Frederic; WELSH, CARLA - Freshwater Institute; KENNEY, P BRETT - West Virginia University; SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Journal of Aquaculture Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2012
Publication Date: 1/29/2013
Publication URL: https://handle.nal.usda.gov/10113/57139
Citation: Davidson III, J.E., Good, C.M., Barrows, F., Welsh, C., Kenney, P., Summerfelt, S.T. 2013. 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. Journal of Aquaculture Engineering. 52: 45-57.

Interpretive Summary: Aquaculture diets are currently being developed to reduce/ replace the use of fish meal and other non-sustainable ingredients with more sustainable yet cost effective ingredients. As alternative ingredient diets are developed for aquaculture, it is important that these diets result in optimal performance and health of the cultured species, but also produce optimal water quality within fish culture systems and minimize nutrient concentrations within aquaculture effluents. This article provides detailed results on water quality concentrations, waste production metrics, and rainbow trout performance metrics related to feeding a zero fish meal, grain-based diet versus a traditional fish meal-based diet within six replicated recirculating aquaculture systems operated using low water exchange and flushing rates. Some key findings from this study included: Total and dissolved phosphorous concentrations in the discharge water were approximately three times lower from recirculating systems fed the zero fish meal, grain-based diet. Therefore, properly formulated grain-based diets may reduce phosphorous discharge and limit pollution and eutrophication within watersheds receiving effluents from aquaculture facilities. The total daily mass of phosphorous produced and captured was also lower within recirculating systems fed the grain-based diet. Feeding the zero fish meal, grain-based diet resulted in significantly greater concentrations of total suspended solids, fine solids, biochemical oxygen demand, and total ammonia nitrogen within the culture system water during the majority of the study period. Increased concentrations of these water quality parameters within recirculating aquaculture systems are not desirable; therefore, we provide key information to nutritionists for the future production and refinement of alternative ingredient diets intended for use within recirculating aquaculture systems. The removal efficiencies measured across each water treatment process of the recirculating aquaculture systems were similar between diet treatments, with the exception of solids removal efficiency across the drum filter and radial flow settler devices. The recirculating aquaculture systems were robust in compensating for water quality differences between diets and maintained water quality that was acceptable for optimal fish health and performance. Rainbow trout fed the grain-based diet grew at the same rate as trout fed the traditional fish meal-based diet. Feed conversion ratio and condition factor were also similar between rainbow trout fed the grain- vs. fish meal-based diets and rainbow trout survival was near 100% for both diets. The grain-based diet evaluated during the present study proved to be a viable feed option for use within a low exchange water recirculating aquaculture system.

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. 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 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. 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 and/or use of ozone to improve water quality when feeding GB diets within low exchange WRAS could be beneficial.