Using Glycerol to Produce European Sea Bass Feed With Oleaginous Microbial Biomass: Effects on Growth Performance, Filet Fatty Acid Profile, and FADS2 Gene Expression

Abstract

Using a circular economy concept, the present study investigated the use of crude glycerol, a primary by-product of biodiesel production, as a low-priced nutrient source for heterotrophic cultivation of the fungus-like protist Schizochytrium limacinum SR21 strain. The whole biomass of this oleaginous microorganism, rich in docosahexaenoic acid (DHA) and high-quality proteins, was then paired with a vegetable oil (VO) source and used to replace fish oil (FO) in European sea bass (Dicentrarchus labrax) feeds. Four nutritionally balanced diets were formulated: diet FO (a FO-based diet), diet VO + 0 (a VO-based diet without S. limacinum), and diets VO + 5 and VO + 10 that were VO-based feeds supplemented with 5 and 10% of S. limacinum, respectively. After a 3-month feeding trial, fish of all dietary groups tripled their initial weight, but growth and feeding efficiencies of D. labrax were not significantly different among treatments. Although the formulated diets were balanced for polyunsaturated fatty acids (PUFAs), fish fed with feeds containing either VO or VO plus 5 and 10% of S. limacinum biomass had significantly higher levels of PUFAs in the flesh than fish fed the FO-based diet. Values of health-related lipid indexes, such as atherogenicity index, thrombogenicity index, and flesh lipid quality as well as n-6/n-3 and PUFAs/SFAs ratios confirmed the high nutritional value of sea bass filet, thus representing a healthy product for human consumption. Although the PUFAs/SFAs ratio showed a significantly higher value in fish fed with VO-based diets supplemented with S. limacinum than in those fed with FO diet, suggesting a better filet quality, the n-6/n-3 ratio clearly indicated that filet quality of dietary group FO was best (value of 0.55) and that of group VO + 10 second best (value of 0.98). We also evaluated the nutritional regulation of Δ6-desaturase (or fads2) gene expression in European sea bass liver. European sea bass fed the VO + 0 diet had the highest number of mRNA copies for Δ6-desaturase (or fads2), fish fed with diet VO + 10 the lowest. Our study adds to the growing body of literature concerning the use of thraustochytrid biomass as a valid alternative to marine-derived raw materials for European sea bass feeds.

Wild and Farmed Sea Bass (Dicentrarchus Labrax): Comparison of Biometry Traits, Chemical and Fatty Acid Composition of Fillets

“…Fillets of extensive reared sea bass showed the lowest value of C16:1n9 (p = 0.002), C16:1n7 (p = 0.006), C17:1 (p = 0.002), C18:1n7 (p = 0.005), and the highest (p = 0.005) value of oleic acid (C18:1 n9), who was identified as the major monounsaturated fatty in cultured and wild sea bass [37][38][39].…”

“…There is a need of a deeper understanding and knowledge on the fatty acid composition and the natural diet of the fish which lives in the salt lake to confirm this hypothesis. The use of formulated feeds rich in n-3 PUFA in aquaculture-desirable from a human nutritional standpoint in consideration of the role played by n-3 PUFA in the prevention of cardiovascular and inflammatory diseases-also has a positive incidence on the growth rate and feed conversion efficiency of fish [14,39].…”

Effects of scale worm parasitism on interactions between the symbiotic gill microbiome and gene regulation in deep sea mussel hosts

“…In addition, the host G. haimaensis parasitized by B. pettiboneaei displayed significant changes in the expression of genes involved in lipid metabolism, such as FADS2 (fatty acid desaturase 2, FC = 1.0167, p = 7.82E-05). FADS2 encodes a protein that is involved in the biosynthesis of unsaturated fatty acids and plays an important role in lipid anabolism, as the first enzyme in the biosynthesis of long-chain fatty acid (≥C20; Terova et al, 2021 ). Similarly, the rate-limiting enzyme diacylglycerol o-acyltransferase in cotton melon aphids parasitized by Lysiphlebia japonica has been found to increase by 3.24 fold, and almost all key genes in the glycerolipid synthesis pathway have been found to be up-regulated with respect to the non-parasitic group ( Zhang et al, 2015 ).…”

Discrimination between Wild and Farmed Sea Bass by Using New Spectrometry and Spectroscopy Methods

“…The differences in DHA/AA between the two groups could be probably explained by the differences in feeding. In the last decade, the feeding industry has promoted the use of ingredients for aquaculture feeding that can improve the levels of ω3 fatty acids and in particular DHA [ 20 ]. However, some studies reported the importance of supplying fish diets not only with ω3-3 PUFA but also with ω6-PUFA to improve growth performance and immune system function [ 21 ].…”