The use of egg quality parameters to evaluate the effect of a diet supplemented with algae and antioxidants in turbot (Scophthalmus maximus)

Abstract

Enhancing egg quality can be achieved by improving breeders' diet through the antioxidant content, as oxidative stress could adversely affect egg quality. Micro- and macroalgae species are natural sources of antioxidants and other essential nutrients that can be incorporated in fish feeds. In this study the quality of Scophthalmus maximus eggs were compared between breeders fed a commercial (non-supplemented) diet and those fed a diet enriched with 5 % Arthrospira platensis and 1 % of the iodine-rich Laminaria digitata, further fortified with antioxidants (astaxanthin, vit. C and E) (supplemented diet). Several egg parameters were evaluated. Hierarchical clustering of all the egg batches grouped them into two main categories: higher (≥ 50 % buoyancy) and lower-quality eggs (≤ 30 % buoyancy). The expression of transcripts related to egg quality (ctsz, ccna2), oxidative response (nrf2, cat), and apoptosis (bax, casp3a) was also measured in batches categorized by quality, as well as in higher-quality batches from females fed the commercial versus supplemented diet. Eggs of higher quality (greater buoyancy), regardless of females' diet, had significantly higher total antioxidant status (TAS) levels (P < 0.05), suggesting TAS as an egg quality marker. The expression of ccna2 was upregulated, while ctsz showed almost no expression in higher-quality eggs but was down-regulated in lower-quality eggs, highlighting their potential as markers of egg quality in turbot. Higher-quality eggs from females fed the supplemented diet exhibited higher TAS, lower superoxide dismutase activity, and an upregulation of nrf2 compared to higher-quality eggs from non-supplemented females. This suggests a more efficient cellular mechanism to restore oxidative homeostasis. Supplementing the diet increased the likelihood of achieving ≥80 % buoyant eggs and overall cumulative egg production, contributing to more effective and sustainable turbot farming.