Abstract
One of the factors that limits the replacement of fish meal (FM) and fish oil (FO) by plant ingredients in diets for marine fish, is their lack of long chain-polyunsaturated fatty acids (LC-PUFA). LC-PUFA are essential fatty acids for these fish species, which lack sufficient fatty acyl desaturase 2 (Fads2) activity to synthesize them. Nutritional programing or the use of broodstock with a higher Fads2 activity could improve marine fish ability to synthesize LC-PUFA and their ability to use low FM and FO diets. The aim of this study was to determine the effect of gilthead seabream broodstock with inherently high or inherently low fads2 gene expression and nutritional programing with broodstock diets rich in FO or rapeseed oil (RO) on the progeny growth performance, liver morphology, biochemical composition and expression of selected genes. Sea bream juveniles (2.31± 0.01 g initial body weight, mean ± SD) obtained from broodstock with either high (H) or low (L) fads2 expression and fed a broodstock diet based on FO or RO were randomly distributed into 12 × 250 L tanks and nutritionally challenged for 45 days with a diet containing only 7.5% FM and no FO. The highest growth was found in juveniles from broodstock with a high fads2 expression and fed the RO diet, whereas the lowest growth was obtained in those from broodstock with a low fads2 expression and fed the RO diet. Juveniles from broodstock with high fads2 expression showed significantly higher fads2 expression in liver and increased PUFA contents in liver and muscle. Replacement of FO by RO in broodstock diets led to a significantly increased hepatic 18:3n-6/18:2n-6 ratio and reduction in the viscerosomatic index of the progeny juveniles, the hepatocyte size and the ghr-1/ghr-2 expression in muscle. Overall, the results showed significant trans-generational effects of both the broodstock fads2 expression and the type of lipid in the broodstock diet on the metabolism and performance of the juvenile progeny challenged with a diet low in FM and FO.
Highlights
Besides being a well-balanced source of minerals and highly digest ible proteins, fish food are the main source of n-3 long chain poly unsaturated fatty acid (n-3 long chain-polyunsaturated fatty acids (LC-PUFA)) for people
Further development of aquaculture is restricted by the limited availability and increasing prices of fishmeal (FM) and fish oil (FO), Abbreviations: ALA, ɑ-linolenic acid; cox2, cycloxigenase-2 gene; cpt-1, carnitin palmitoil transferase 1 gene; docosa hexaenoic acid (DHA), docosahexaenoic acid; elovl6, elongase 6 gene; EPA, eicosapentaenoic acid; fatty acyl desaturase 2 (Fads2), Fatty acyl desaturase 2; fads2, Fatty acyl desaturase 2 gene; FAMES, fatty acid methyl esters; FCR, feed conversion ratio; FI, feed intake; FM, fishmeal; FO, fish oil; gh, growth hormone; Ghr, Growth hormone receptor; Hepatosomatic index (HSI), hepatosomatic index; LC-PUFA, long-chain polyunsaturated fatty acid; Lpl, lipoprotein lipase; LNA, linoleic acid; LO, linseed oil; OA, oleic acid; PA, palmitic acid; RO, rapeseed oil; rpl-27, ribosomal protein l27 gene; SGR, specific growth rate; tnf-α, tumor necrosis factor-alpha gene; Viscerosomatic index (VSI), viscerosomatic index
At the end of the trial, the largest growth in terms of body weight, weight gain and SGR were found in juveniles from broodstock with high fads2 and fed RO diet (HRO), whereas the lowest was found in juveniles obtained from broodstock with low fads2 and fed RO diet (LRO) (Fig. 2, Table 4)
Summary
Besides being a well-balanced source of minerals and highly digest ible proteins, fish food are the main source of n-3 long chain poly unsaturated fatty acid (n-3 LC-PUFA) for people. Due to the stagnant production of fisheries, aquaculture is taking over the responsibility to provide safe and sustainable fish food to satisfy market demands (FAO, 2020). Many alternative feedstuffs are used to replace FM and FO in aquafeeds such as plant ingredients, animal byproducts, single cell ingredients or insect meals (Caballero et al, 2002; Rimoldi et al, 2018; Rosales et al, 2017; Wang et al, 2016). Depending on the type of ingredient and the replacement level, these alternative feedstuffs may lead to malnu tritional effects on fish growth, nutrients digestibility, immune system, etc. (Caballero et al, 2004; Castro et al, 2015; Gomez-Requeni et al, 2004; Vergara et al, 1996a; Vergara et al, 1996b)
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