Effects of feeding a fishmeal-free versus a fishmeal-based diet on post-smolt Atlantic salmon salmo salar performance, water quality, and waste production in recirculation aquaculture systems

Authors: DAVIDSON, JOHN - Freshwater Institute; Barrows, Frederic; KENNEY, P. BRETT - West Virginia University; GOOD, CHRISTOPHER - Freshwater Institute; SCHROYER, KAREN - Freshwater Institute; SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2016
Publication Date: 5/18/2016
Citation: Davidson, J., Barrows, F., Kenney, P., Good, C., Schroyer, K., Summerfelt, S.T. 2016. Effects of feeding a fishmeal-free versus a fishmeal-based diet on post-smolt Atlantic salmon salmo salar performance, water quality, and waste production in recirculation aquaculture systems. Aquacultural Engineering. 74:38-51. doi: 10.1016/j.aquaeng.2016.05.004.

Interpretive Summary: It is not only important that alternative ingredient diets developed for aquaculture 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. Atlantic salmon raised in recirculating aquaculture systems operated using low water exchange and flushing rates, were fed fish meal free (FMF) versus a traditional fish meal-based diet . Atlantic salmon growth, survival, and feed conversion ratios (FCR) were unaffected by diet; however, water quality measures were affected. Total and dissolved phosphorous concentrations, carbonaceous biochemical oxygen, and total suspended solids produced and captured were higher within recirculating systems fed the FMF diet. Increased concentrations of these water quality parameters within recirculating aquaculture systems are not desirable; therefore, the study provided key information to nutritionists for the future production and refinement of alternative ingredient diets intended for use within recirculating aquaculture systems. Nevertheless, 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. This was the first research attempt to formulate a fishmeal-free diet for Atlantic salmon with this ingredient profile and one of few studies to demonstrate uncompromised Atlantic salmon performance when feeding a diet without fishmeal.

Technical Abstract: The Atlantic salmon farming industry has progressively decreased the proportion of fishmeal used in commercial diets due to rising costs and sustainability concerns. A variety of alternate proteins have been identified to partially replace fishmeal; however, very little research has described the effect of feeding alternate protein, fishmeal-free diets to Atlantic salmon, particularly post-smolts cultured in recirculation aquaculture systems (RAS). Therefore, a 6-month study was conducted to compare the effects of feeding a fishmeal-free diet (FMF) versus a fishmeal-based diet (FM) on post-smolt Atlantic salmon performance, water quality, and waste production rates in six replicated RAS. Experimental diets were fed to Atlantic salmon (281 plus or minus 5 g to begin) in triplicate RAS. Protein ingredients used in the FMF diet included mixed nut meal, poultry meal, wheat flour, and corn protein concentrate; while the FM diet contained menhaden meal, poultry meal, soy protein concentrate, and blood meal proteins. Fish oil derived from whiting fish trimmings was used in the FMF diet to establish a wild fisheries input to farmed fish output ratio of 0:1; while menhaden oil was the primary lipid source for the FM diet. Both diets were formulated with approximately 42% crude protein and 27% crude fat. Each RAS was operated with flushing rates that created an average system hydraulic retention time of 20 days (5% system volume flushed daily) and a mean feed loading rate of 3.2 kg feed/m3 of daily make-up water volume. Atlantic salmon growth, survival, and feed conversion ratios (FCR) were unaffected (P greater than 0.05) by diet. At the conclusion of the study, Atlantic salmon fed the FMF and FM diets were 1.716 plus or minus 0.076 and 1.720 plus or minus 0.065 kg; cumulative survival was greater than 99% for both; and average FCR was 0.89 plus or minus 0.03 and 0.90 plus or minus 0.02, respectively. The FMF diet resulted in greater total phosphorous (TP), carbonaceous biochemical oxygen (cBOD), and total suspended solids (TSS) mass per kg feed in the effluent (P less than 0.05). The FMF and FM diets produced 0.009 plus or minus 0.001 v. 0.006 plus or minus 0.001 kg TP/kg feed; 0.079 plus or minus 0.005 v. 0.056 plus or minus 0.005 kg cBOD/kg feed; and 0.297 plus or minus 0.028 v. 0.221 plus or minus 0.032 kg TSS/kg feed, respectively. A significantly higher percentage of TSS was captured by radial flow settlers of RAS receiving the FMF diet compared to capture by settlers associated with the FM diet. Mass balance data, radial settler removal efficiency, and observations of flushed solids suggested that the FMF diet produced fecal matter with better settling characteristics. Lower TSS and true color values (P less than 0.05), indicative of clearer water, were measured in RAS receiving the FMF diet. Total phosphorous (most of which was dissolved) was 4 times greater in the culture water of RAS that received the FMF diet, e.g., 4.3 plus or minus 0.1 mg/L v. 0.9 plus or minus 0.0 mg/L for the FM Diet. This was the first research attempt to formulate a fishmeal-free diet for Atlantic salmon with this ingredient profile and one of few studies to demonstrate uncompromised Atlantic salmon performance when feeding a diet without fishmeal.