Introduction
In the last decades, plant feedstuffs (PF) have sustained aquafeed formulation to face the increase in aquaculture production and the need for fish meal and oil replacement in diets. However, the use of PF can be limited due to antinutrient presence, amino acid imbalances, lower nutrient digestibility, and palatability (Naylor et al. 2021). Using PF mixtures coupled with amino acid and attractants supplementation is a suitable strategy to mitigate the limitations of specific ingredients (Gatlin et al., 2007). Nevertheless, non-starch polysaccharides (NSP), which fish cannot digest, may impair intestinal health, feed utilization, and, ultimately, fish growth (Sinha et al., 2011). Moreover, differences in the NSP profile of PF can affect fish physiological responses and the gut-microbiome axis. This study evaluated the effects of oilseed-rich diets with varying NSP profiles on growth performance, gut health, and functionality in gilthead seabream.
Materials and Methods
Five diets were formulated to be isoproteic (45% dry weight) and isolipidic (18% dry weight) and include 30% of either soybean, rapeseed, or sunflower meal, a mix of 10 % of each ingredient, and a control diet without these ingredients. Triplicate groups of gilthead seabream (Sparus aurata) with 95g initial weight were fed the experimental diets to satiety for 65 days. The following parameters were assessed: Growth performance, gut morphology, liver composition, plasma metabolites, digestive enzymes activity, and mucosal microbiome (bacteria and fungi) composition.
Results
Growth, feed efficiency, and body composition were unaffected by diet composition. Gut morphology showed minimal changes, except for reduced goblet cells and increased supranuclear vacuolization in fish fed the soybean diet. Fish fed the sunflower diet exhibited the lowest hepatosomatic index (HSI), liver lipid and glycogen levels, and plasma glucose. Plasma triglycerides were higher in soybean and rapeseed groups, while plasma cholesterol was higher in soybean and sunflower groups. Amylase and lipase activities were higher in fish fed the rapeseed diet. The mucosal microbiome, particularly the fungal community, was affected by dietary treatment. A comprehensive evaluation of the results is provided in Figure 1.
Conclusion
PF-based diets with up to 30% soybean, rapeseed, or sunflower meal supported healthy growth in gilthead seabream with minimal impact on gut health. Although zootechnical performance remained unaffected, differences in dietary carbohydrate profiles, specifically the high-starch/low-fiber in the control diet versus the low-starch/high-fiber in the sunflower diet, affected plasma glucose levels, HSI, and liver composition. Results indicate that dietary carbohydrate profile markedly influenced mycobiota.
Acknowledgement
This research was funded by national funds through FCT – Foundation for Science and Technology within the scope of the Strategic Funding UIDB/04423/2020, UIDP/04423/2020, and LA/P/0101/2020. P.G has a PhD scholarship (https://doi.org/10.54499/2022.00885.CEECIND/CP1728/CT0013), both supported by FCT.
Reference
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Naylor RL, Hardy RW, Buschmann AH, Bush SR, Cao L, Klinger DH, Little DC, Lubchenco J, Shumway SE, Troell M (2021) A 20-year retrospective review of global aquaculture. Nature 591:551–563.
Sinha, A. K., Kumar, V., Makkar, H. P. S., De Boeck, G., and Becker, K. (2011). Nonstarch polysaccharides and their role in fish nutrition - A review. Food Chem. 127, 1409–1426.