Abstract
Efforts have been made to find natural, highly nutritious alternatives to replace fish meal (FM) and fish oil (FO), which can simultaneously promote fish health and improve the nutritional quality of filets for human consumption. This study evaluated the impact of biofortified diets containing microalgae (as replacement for FM and FO), macroalgae (as natural source of iodine) and selenised yeast (organic source of selenium) on gilthead seabream growth, nutrient utilization, tissue composition and gene expression. A control diet (CTRL) with 15% FM and 5.5% FO was compared with three experimental diets (AD1, AD2, and AD3), where a microalgae blend (Chlorella sp., Tetraselmis sp., and DHA-rich Schizochytrium sp.) replaced 33% of FM. Diet AD1 contained 20% less FO. Diets were supplemented with Laminaria digitata (0.4% AD1 and AD2; 0.8% AD3) and selenised yeast (0.02% AD1 and AD2; 0.04% AD3). After feeding the experimental diets for 12 weeks, growth was similar in fish fed AD1, AD2, and CTRL, indicating that microalgae meal can partially replace both FM and FO in diets for seabream. But AD3 suppressed fish growth, suggesting that L. digitata and selenised yeast supplementation should be kept under 0.8 and 0.04%, respectively. Despite lower lipid intake and decreased PUFAs bioavailability in fish fed AD3, compared to CTRL, hepatic elovl5 was upregulated resulting in a significant increase of muscle EPA + DHA. Indeed, filets of fish fed AD2 and AD3 provided the highest EPA + DHA contents (0.7 g 100 g–1), that are well above the minimum recommended values for human consumption. Fish consuming the AD diets had a higher retention and gain of selenium, while iodine gain remained similar among diets. Upregulation of selenoproteins (gpx1, selk, and dio2) was observed in liver of fish fed AD1, but diets had limited impact on fish antioxidant status. Overall, results indicate that the tested microalgae are good sources of protein and lipids, with their LC-PUFAs being effectively accumulated in seabream muscle. Selenised yeast is a good fortification vehicle to increase selenium levels in fish, but efforts should be placed to find new strategies to fortify fish in iodine.
Highlights
Fish are major dietary sources of high-quality proteins, vitamins (i.e., D, A and B12), n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs), mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), iodine, selenium and iron for human consumption (EFSA, 2014), so farmed products must provide adequate levels of such nutrients for consumers.Gilthead seabream (Sparus aurata) is one of the main marine fish species for aquaculture production in the Mediterranean region (FAO, 2020)
Feed ingredients and diet compositions are summarized in Table 1: a control diet (CTRL) with moderate fish meal (FM) (15%) and fish oil (FO) (5.5%) contents was compared with three experimental diets (AD1, AD2. and AD3) with 33% FM replaced with microalgae meal (Chlorella sp., Tetraselmis sp. and DHA-rich Schizochytrium sp.) and reduced vegetable oil contents (11% reduction in soybean, rapeseed, and linseed in AD1 and between 21–23% reduction in AD2 and AD3)
At the end of 12 weeks of feeding, fish fed the CTRL diet reached a final body weight (FBW) of 625.8 ± 5.4 g, that was similar to that of fish fed with AD1 and AD2
Summary
Fish are major dietary sources of high-quality proteins, vitamins (i.e., D, A and B12), n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs), mainly EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), iodine, selenium and iron for human consumption (EFSA, 2014), so farmed products must provide adequate levels of such nutrients for consumers.Gilthead seabream (Sparus aurata) is one of the main marine fish species for aquaculture production in the Mediterranean region (FAO, 2020). Plant-based products are commonly used as substitutes for fish meal (FM) and fish oil (FO) in diets for several carnivorous farmed fish, but previous studies have shown that complete, or even partial, replacement of FM and FO with plant proteins (PP) and vegetable oils (VOs) in diets for S. aurata can compromise fish health and nutritional value of filets for human consumption (Izquierdo et al, 2005; Montero et al, 2008; Matos et al, 2017; Estruch et al, 2018) In this context, diets for farmed fish using natural products, such as selected microalgae (rich in nutrients including LC-PUFAs and bioactive compounds), seaweeds (rich in iodine) and selenised yeast (rich in selenium), with proven beneficial effects for both fish performance and filet quality, are of interest to both the scientific community and aquaculture sector (Vizcaíno et al, 2016; Ribeiro et al, 2017; Wang et al, 2018; Granby et al, 2020; Valente et al, 2021). New fortification strategies are required to maximize deposition of beneficial compounds contributing to the functional foods market in parallel with securing fish health
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