Metabolism, health and fillet nutritional quality in Atlantic salmon (Salmo salar) fed diets containing n-3-rich microalgae

Abstract

Microalgae, as primary producers of EPA and DHA, are among the most prominent alternative sources to fish oil for n-3 long-chain PUFA in animal and human nutrition. The present study aimed to assess technical, nutritional and fish health aspects of producing n-3-rich Atlantic salmon (Salmo salar) fish fillets by dietary supplementation of increasing levels of a DHA-producing Schizochytrium sp. and reduced or without use of supplemental fish oil. Atlantic salmon smolt were fed diets with graded levels of microalgae for 12 weeks, during which all fish showed high feed intake rates with postprandial plasma leptin levels inversely correlating with final mean fish body weights. Fish performance was optimal in all experimental treatments (thermal growth coefficient about 4·0 and feed conversion ratio 0·8–0·9), protein digestibility was equal in all diets, whereas dietary lipid digestibility inversely correlated with the dietary levels of the SFA 16 : 0. Fillet quality was good and similar to the control in all treatments in terms of n-3 long-chain PUFA content, gaping, texture and liquid losses during thawing. Histological fluorescence staining and immunofluorescence analysis of salmon intestines (midgut: base of intestine and villi) revealed significant effects on slime, goblet cell production and inducible nitric oxide synthase (iNOS) activity with increasing levels of dietary Schizochytrium sp. supplementation. Microarray analysis did not reveal any signs of toxicity, stress, inflammation or any other negative effects from Schizochytrium sp. supplementation in diets for Atlantic salmon.

Nannochloropsis oceania-derived defatted meal as an alternative to fishmeal in Atlantic salmon feeds

“…The TGC values in the present experiment were higher than those obtained by Sørensen et al [15], but were in the same range as reported by Hatlen et al [26]. Feed conversion rate was in line with studies performed on yeast- or microalga-fed Atlantic salmon of sizes comparable to that used in the present study [26, 27]. The dry matter intake (for each kg wet weight gain) of fish fed the highest inclusion level of defatted N .…”

Growth phase significantly decreases the DHA-to-EPA ratio in marine microalgae

“…For R. salina, which contains significant percentages of both DHA and EPA and is used as aquaculture feed (e.g., Gagné et al 2010), this would imply that although the total cellular amount of fatty acids is higher, the nutritional value of this species is lower at the end of the growth phase. Currently, several microalgal species are being investigated by the aquaculture industry as fish meal or fish oil replacement in the diet of commercially farmed fish (Kousoulaki et al 2015;Sprague et al 2015;Sørensen et al 2016). Replacing the traditional EPA-and DHA-rich, but finite, marine ingredients, fishmeal and fish oil present a significant challenge for the aquaculture industry (Sprague et al 2016).…”

“…Promising fish oil alternatives are lipids from microalgae which can potentially grow at high growth rates and which can reach high maximum cell densities with high levels of EPA and/or DHA. Much research has been focused on heterotrophic DHA-producing species such as Schizochytrium (Kousoulaki et al 2015;Sprague et al 2015). However, Sprague et al (2015) showed that the absence of EPA in Schizochytrium-based fish diet significantly impairs the overall nutritional value.…”

“…Cultivated marine algae can be used directly, as live feed for (larval stages of) bivalves and crustaceans, or indirectly, as food for zooplankton such as rotifers which, in turn, are used to feed crustaceans or small fish larvae (Muller-Feuga 2000;Chauton et al 2014). Besides this, several microalgal species are currently being investigated by the aquaculture industry as fish meal or fish oil replacement in the diet of commercially farmed fish (Kousoulaki et al 2015;Sprague et al 2015;Sørensen et al 2016). Marine algae are key organisms in the production of essential long-chain polyunsaturated fatty acids (LC-PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).…”

Applications of microalga Chlorella vulgaris in aquaculture

“…An enzyme responsible for nitric oxide synthesis, called inducible nitric oxide synthase (iNOS) is the key protein in intestinal immunity, as it controls inflammatory cytokines such as TNFα (Kousoulaki et al . ). The enzyme regulates both the baseline mucus production in the gut, thus mitigating the damage to the intestinal mucosal lining due to inflammatory diseases (Schreiber et al .…”