Insoluble Canola Protein Concentrate Partially Replaces Fish Meal in Largemouth Bass Diets without Affecting Growth Performance

Sustainability of carnivorous finfish aquaculture depends on reducing the industry’s reliance on fish meals (FM) and oils.  However, replacing FM with plant-derived protein sources often negatively impacts growth due to decreased palatability, nutrient availability, and/or nutrient utilization associated with the alternative protein.  Insoluble canola protein concentrate (ICPC) has similar crude protein content and amino acid profile to that found in menhaden FM, and may be more suited to aquafeeds than other plant-derived proteins.  Accordingly, we monitored largemouth bass (LMB) production performance while replacing dietary FM with ICPC.

 Juvenile LMB (28.6 ± 0.1 g; mean initial wt ± SE) were stocked into a recirculation system (10 fish/tank).  Triplicate tanks were fed diets (44% crude protein and 14% crude lipid) containing graded levels (0, 8, 16, or 24%) of FM and (24, 16, 8, or 0%, respectively) ICPC twice daily to apparent satiation for 12 weeks.  Other ingredients in the diet providing dietary protein included: soybean meal, blood meal, poultry by-product meal, and wheat bran.

 Fish fed the 0% FM diet were significantly smaller at the end of the trial compared to those fed 8% FM (76.0 ± 2.6 g and 87.9 ± 2.6 g, respectively) even though fish fed the 0% FM diet consumed similar quantities of feed as those fed 8 and 16% FM and significantly more feed than those fed 24% FM. Largemouth bass feed conversion ratios (FCR) were significantly lower when fed the 0% FM diet (2.6 ± 0.1) compared to when fed the 8% FM (2.1 ± 0.1) and 24% FM diets (2.1 ± 0.1).  No statistical differences in weight gain were observed.

 Palatability of ICPC does not appear to be a problem for LMB fed FM-free diets, as feed intake was actually higher among fish fed lower quantities of FM.  Increased FCR observed among the LMB fed the 0% FM diet may be due to lower nutrient availability or utilization associated with ICPC compared to FM, even though ICPC has an amino acid profile similar to FM.  Largemouth bass appear to be able to compensate for presumably reduced nutrient availability in the 0% FM feed by increasing feed intake, resulting in broadly comparable growth among all groups at the end of the trial.  Based on these results, a diet containing 8% FM with supplemental protein supplied from ICPC yields adequate growth in LMB and represents more efficient utilization of FM in feeds for this carnivorous species.