COMMERCIAL DEVELOPMENT OF RAS-SPECIFIC DIETS: EVALUATING EFFECTS ON WATER QUALITY AND ATLANTIC SALMON Salmo salar PERFORMANCE

Increas ed  investment  in land-based , recirculating aquaculture systems (RAS) is driving demand for special ly formulated diets that are compatible  with water quality and waste discharge  in addition to  fish performance .  For example,  RAS-specific  diets  must produce intact  and settleable  fecal material that is  less prone to disintegration and release  of fine particles and  dissolved nutrients . Specialty d iets  for the  production of  market-size  Atlantic salmon  in RAS  are in particular demand, as  commercial development of this  aquaculture sector has grown rapidly over the last decade.

T o support this industry need, the Freshwater Institute  recently  partnered with  commercial feed supplier Cargill Inc. to evaluate four diets  fed to post-smolt Atlantic salmon (1.77 kg initial weight) with in  twelve  replicated water reuse systems. A 2x2 factorial design was employed to evaluate d iets  that: i ) inc luded or exclu ded a proprietary binder-like ingredient (B), and  ii)  were formulated with  either land animal (LAP) or fishmeal-based (FM) proteins (N=3) . Water quality, with focus on  total suspended solids (TSS), was  comprehensively  assessed throughout the 6-month trial , and fish performance metrics were evaluated bimonthly .

A highly significant difference in TSS  concentration was detected (P = 0.000)  in the culture water of reuse systems  relative to inclusion of the binder-like ingredient (Fig. 1) . Trends for increased s olids settleability as measured by TSS levels in the cone-bottom and overtopping flows of settling devices suggested improved fecal stability for diets containing the binder. Significantly lower fine particle (2-30 µm )  counts were also associated with these diets.                    Fig. 1.  Culture tank  TSS levels associated with each diet.

A difference in  growth as measured by  mean salmon weight  was detected between treatments (P= 0.000) at each sampling interval , where  fishmeal-based diets resulted in faster growth than  diets formulated with land animal proteins.  Statistical differences in survival and fish health metrics were not found . Overall, t his trial  provided  data-driven  proof-of-concept for the development of  a  RAS-specific  diet for  post-smolt Atlantic salmon growing towards market-size.