Updated September 1, 2023:
In the first objective of this work, we sought to compare our fishmeal free high soy practical diet (8% poultry meal, 10% corn protein concentrate, 55% soybean meal) with a commercial feed commonly used to rear the Florida pompano. Thus, providing validation of the high soy open feed formulation that we use in research. This work was conducted in two independent systems (Referred to as Trials 1 and 2 in attached tables). Juvenil fish (23.2g) were reared in our smaller tank (800 L) recirculation system using six replicates for each diet. At the conclusion of the 6-week growth final weight (55.2 and 60.4g, P=0.076), percent weight gain (138.8% and 160.0%; P=0.006) and FCR (2.05, 1.86; P= 0.015) for fish reared on the experimental feed were poorer but not necessarily significantly than that of fish reared on the commercial feed. A similar response was observed in our large tanks system (3,000 L) which utilized three replicate groups of larger fish with an initial mean weight of 38.1g. At the conclusion of the 8-week growth trial final weights (125g and 137g; P-value 0.3318), percent weight gain (226.1% and 269.2 %; P = 0.284) and FCR (2.05 and 1.89; p= 0.577) were not statistically different. In both cases, performance was lower, albeit not necessarily significantly (P < 0.05) in fish offered the experimental diet as compared to the commercial feed. This would indicate that although we were very close in terms of performance, we still need to optimize diets that have low levels of animal protein and high levels of plant-based proteins.
Samples of the distal gut were collected from fish reared in the 8-week trial. These samples were sectioned and stained. The lamina propria thickness and cellularity, as well as vacuolization and connective tissue thickness were evaluated. The slides were scored with no clear signs of enteritis noted. Based on the available data, enteritis is not present in high soy feed formulations which would indicate that other nutritional or antinutrients are responsible for any reduced performance.
The second component of this research was to evaluate various soybean sources. For this work different processed soybean meal products were sourced including: new variety; high protein low oligosaccharide solvent-extracted soybean meal (Benson Hill, St. Louis, MO, USA), fractionated soy protein concentrate (Soycomil, ADM Animal Nutrition, Quincy, IL, USA), fermented soybean meal (Hamlet HP300, Hamlet Protein Inc., Findlay, OH, USA), and modified expeller-pressed soybean meal (All Sustained LLC., Shrewsbury, USA) were used in diets. The idea was that the various processing methods would result in different antinutrient levels and potentially result in improved performance. The basal diet and 8 test diets were formulated (Tables 3 and 4, attached) to have equivalent levels of protein and lipids. Test diets were developed by replacing soybean meal (on an equal protein basis) with each product (Bright Day, Hamlet HP300, and Soycomil) at 50% and 100% replacement. Expeller-pressed soy was used only to replace 25% and 50% of the soybean meal. The growth trial was run at E. W. Shell Fisheries Center under controlled conditions in a recirculating aquaculture system. Four replicate groups of fish (4.82g mean weight) were assigned to each dietary treatment and reared over a 76-day culture period. At the conclusion of the growth trial (Tables 6 and 7, attached), there were no significant differences in terms of final weight (32.4 to 45.9g), percent gain (587.7 to 840.1%), FCR (1.88-2.19) or survival (86.6-97.5%). Although, the lack of statistically different results is disappointing. The lack of difference is, in my opinion, due to the variability of this fish as opposed to no biological response. In all replacement products, the fish were numerically larger or had higher weight gain as compared to those reared on solvent-extracted soybean meal, indicating that these products are likely of higher quality. For this work, we also preserved distal gut samples to confirm the histology of the initial trial. The samples have been processed, but histological quantification and qualitative scoring is ongoing. The results from this study will be compiled, presented at scientific meetings, and a paper will be developed from the data.
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The take-home message from this work is that comparing a practical soy-maximized diet to a commercial feed formulation commonly used with Florida pompano that there is a slight depression in growth. Thus, demonstrating that we are very close to using high soy feed formulations (based on solvent-extracted soybean meal) for this species. Histological evaluations of the gut from these fish are underway and preliminarily demonstrate that there is no enteritis (allergic response to soy). This likely means that the observed growth depressions in performance are due either to the presence of antinutrients or inadequacies in nutrition of the feed. Hence, looking at other soy products with lower levels of antinutrients may lead to better performance. This is what the second and ongoing component of the research is doing. We are looking at various advanced soy products and the effects in high soy feed formulations. Results of this work will add to the literature on use of soy-based product in practical feed formulations for this species.