ASSESSING THE NUTRITIONAL VALUE OF NOVEL SOYBEAN MEALS IN THE DIET OF LARGEMOUTH BASS Micropterus salmoides

Owing to the limited supply, market dynamics, and escalating prices, the aquaculture industry has witnessed a rapid shift from over-reliance on FM towards the use of more sustainable feed ingredients. Among these, soybean meal (SBM) is the foremost protein ingredient currently used in aquafeeds. However, soybean antinutritional factors can cause adverse effects in the fish, reducing production performance and survival, thereby leading to species-specific upper limits for dietary SBM. Novel processing technologies were developed to overcome such nutritional limitations and the resulting novel SBMs have potential for use in aquafeeds. Therefore, the present study aimed at assessing the relative nutritional value of a pool of commercially available SBMs in the diet of largemouth bass (LMB).

A 10-week feeding trial was conducted to evaluate three SBM products as surrogates for fish meal (FM) in the diet of LMB. Following an incomplete 2 × 3 factorial design including two FM replacement levels (50 and 75%), three SBM types (SBM-A, B and C), and a 35% FM control diet (FM-35), seven isonitrogenous (42% CP) and isolipidic (12% lipid) experimental diets were formulated. Each experimental diet was fed twice daily to triplicate groups of 15 LMB juveniles (15.3 ± 0.32 g/fish) stocked in 110-L glass aquaria operating as a recirculating aquaculture system.

Figure 1. Weight gain and feed efficiency of largemouth bass fed the experimental diets for 10 weeks. No interactions between FM replacement level and SBM type were found (P>0.05). Error bars represent SE.

At the end of the feeding trial, survival was above 90% for all treatments and was unaffected (P>0.05) by diet. Feeding rate ranged from 3.4 to 4.1% BW/day and was significant higher for LMB fed the SBM - C diets. Despite higher feeding rate, fish in the SBM-C treatments displayed significantly lower weight gain, and feed efficiency compared to those fed SBM-A and SBM-B diets. Both SBM-A and SBM-B could replace 75% of the FM in the FM-35 diet without affecting the production performance of juvenile LMB. We also found significant (P = 0.04) and marginally significant (P = 0.08) detrimental effects on final weight (not shown) and weight gain of LMB, respectively, when FM replacement increased from 50 to 75%. These effects were likely caused by SBM-C diets alone since no other dietary treatment differed from FM-35 as analyzed using Dunnett's test (P>0.05). Significant effects of dietary treatments were also observed on some of the analyzed blood parameters of LMB, which will be presented.

Dietary FM can be reduced from 35 to 8.8% replaced by SBM-A or SBM-B without detrimental effects on the production performance of LMB. Additional studies are warranted to further optimize SBM-based diets for this species.