Performance, Nutrient Digestibility and Physiological Resilience of Juvenile Gilthead Seabream (Sparus aurata) Fed Organic and Circular Economy-Derived Diets

Abstract

Aquafeeds formulated with organic or circular economy-derived ingredients aim to enhance sustainability and consumer acceptance. This study evaluated the global warming potential (GWP) and digestibility of such feeds, and assessed their effects on performance, feed utilisation and physiological resilience, defined as the ability to maintain tissue function and integrity under different feeding conditions of juvenile gilthead seabream (Sparus aurata) during grow out and after an overcrowding stress challenge. Three isonitrogenous (~51% crude protein) and isoenergetic (~18% crude fat) diets with limited fishmeal were formulated: a control (CTRL) commercial-like feed; an organic (ORG) diet based on organic-certified ingredients rich in plant proteins (primarily pea protein concentrate and wheat gluten); an eco-efficient (ECO) diet mainly composed of circular economy-derived animal by-products (e.g., poultry meal and feathermeal hydrolysate). The GWP was estimated using a life cycle assessment. Juvenile seabream (~14 g) were stocked in triplicate 500 L tanks (90 fish per tank, initial density of 2.5 kg/m³) and fed three times daily following feeding tables generated by FiT Feeding Tables, to optimise ration and minimise waste, over a 65-day growth period (final density of 8 kg/m³) and a subsequent 14-day overcrowding challenge (initial density of 12.4 kg/m³). At the end of the growth period, all groups exhibited at least a threefold increase in body weight. Feed digestibility was high (apparent digestibility coefficients (ADCs) > 60%) and utilisation efficient. Physiological resilience was supported by stable growth and relative expression of biomarkers for gut health, oxidative status and immune function. Although ORG and ECO diets showed a higher GWP, this impact may decrease with increased use of renewable energy in ingredient production. The ORG diet also improved fish phosphorus retention. These organic and circular economy-derived feeds present viable options to reduce aquaculture's environmental footprint while maintaining fish performance and resilience.

Keywords: aquafeeds; fish performance; fish resilience; gilthead seabream; global warming potential.

Figure 1

Daily phosphorus (P) balance (mg P/kg fish/day) in gilthead seabream (Sparus aurata), after 65 days of feeding (growth period) with three different experimental diets (CTRL, ORG and ECO). Data are presented as means ± standard deviation (n = 3). Different superscript letters indicate significant differences (one-way ANOVA; p < 0.001) between dietary treatments among the same fraction.

Figure 2

Relative expression (mRNA relative expression) of genes encoding for (a) oxidative status (sod, cat, gpx and nrf2), (b) immune condition (il-1β, igm and cox2) and (c) intestinal epithelium integrity (muc13, cldn12, tjp2, ocl and pcna) in the anterior intestine of gilthead seabream (Sparus aurata) juveniles, after feeding with three different experimental diets (CTRL, ORG and ECO), analysed pre- and post-stress. Data are presented as mean ± standard deviation (n = 3 tanks per dietary treatment). Different superscript letters (CTRL: a and b; ORG: A and B; ECO: α and β) indicate significant differences (planned contrasts one-way ANOVA; p < 0.05) between sampling periods (growth vs. challenge) among the same dietary treatment. Genes within lines on top with p value indicate significant differences (planned contrasts one-way ANOVA; p < 0.05) between sampling periods (growth vs. challenge) while considering all dietary treatments. Molecular biomarkers abbreviations same as in Table 7.

Figure 3

Score plot from the principal component analysis (PCA) based on the relative gene expression in the anterior intestine of gilthead seabream (Sparus aurata) juveniles, after feeding with three different experimental diets (CTRL, ORG and ECO), analysed pre- and post-stress. The first two principal components (PC1 and PC2) are shown on the axis. Scores were grouped by experimental diet (CTRL, ORG and ECO), pre- and post-stress. Each point represents the projection of an individual sample in the PC1 and PC2 axes. The ellipses represent 95% confidence intervals around the centroid (larger point) of each data cluster. Cos2 scale indicates variable loadings. Pre-CTRL, Post-CTRL, Pre-ORG, Post-ORG, Pre-ECO, Post-ECO: fish fed diet CTRL, ORG or ECO, respectively, at the end of the growth (pre-) or challenge (post-) period. Molecular biomarkers abbreviations same as in Table 7.