Growth, Chemical Composition, Histology and Antioxidant Genes of Atlantic Salmon (Salmo salar) Fed Whole or Pre-Processed Nannochloropsis oceanica and Tetraselmis sp.

Solveig Lysfjord Sørensen,Viswanath Kiron,Ghana Vasanth,Mette Sørensen,Ateshm Ghirmay,Dalia Dahle,Yangyang Gong

doi:10.3390/fishes6030023

Solveig Lysfjord Sørensen, Viswanath Kiron + Show 5 more

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https://doi.org/10.3390/fishes6030023

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Journal: Fishes	Publication Date: Jul 23, 2021
Citations: 9	License type: CC BY 4.0

Affiliation: Nord University

Abstract

New sustainable feed ingredients are a necessity for the salmon aquaculture industry. In this study, we examined the effect of pre-extrusion processing of two microalgae, Nannochloropsis oceanica and Tetraselmis sp., on the growth, fatty acid content in the flesh and health of Atlantic salmon. The fish were fed one of the following five diets for nine weeks: (1) CO: a fish meal-based control (basal) diet, (2) NU: a Nannochloropsis diet, (3) NE: a pre-extruded Nannochloropsis diet, (4) TU: a Tetraselmis diet, and (5) TE: a pre-extruded Tetraselmis diet. The algae-incorporated diets contained 30% of the respective microalgae. Our results showed that the best growth performance was achieved by the CO diet, followed by the NE diets. Feeding of unprocessed Nannochloropsis and Tetraselmis resulted in a significant reduction in enterocyte vacuolization compared to the CO feeding. A significant effect of processing was noted in the fillet fatty acid content, the intestine and liver structure and the expression of selected genes in the liver. The expression of antioxidant genes in both the liver and intestine, and the accumulation of different fatty acids in the fillet and liver of the extruded algae-fed groups, warrants further investigation. In conclusion, based on the short-term study, 30% inclusion of the microalgae Nannochloropsis oceanica and Tetraselmis sp. can be considered in Atlantic salmon feeds.

Highlights

Marine microalgae are primary producers of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and, based on their chemical composition, certain microalgae can be good candidates for ingredients in fish feeds if they can be produced on a large scale [1]
A variety of microalgae species has been studied to assess their suitability as feed ingredients for aquaculture in general, and as replacements for fish meal or fish oil in feeds for Atlantic salmon (Salmo salar) [2–8]
Mucins are a diverse group of glycoproteins that are vital components of mucus, and these molecules are responsible for the viscoelastic properties of mucus

Summary

Introduction

Marine microalgae are primary producers of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and, based on their chemical composition, certain microalgae can be good candidates for ingredients in fish feeds if they can be produced on a large scale [1]. Some of the microalgae are good sources of vitamins, minerals and pigments, all with good antioxidant effects [9]. Feeding fish with microalgae meal, which are sources of natural antioxidants, may increase their cells’ capacity to scavenge reactive oxygen (ROS) or nitrogen species. The vital ROS buffering systems in mitochondria and peroxisomes include glutathione peroxidases (GPx), glutathione (GSH), superoxide dismutase (SOD) family of proteins and catalase that help in converting radicals into unharmful substances [12]. Living organisms have developed different antioxidant defence systems to counterbalance the adverse effects of ROS. In addition to these antioxidant mechanisms, rapid and continuous renewal of secreted mucus safeguards the epithelial cells such as those of the intestine [13]. Mucins can be either monomeric or multimeric, and the former group includes transmembrane mucins mainly associated with the glycocalyx, while the latter group are gel-forming mucins, like MUC2, MUC5AC, MUC5B and MUC6 [18–20]

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