Performance, feed utilization, and hepatic metabolic response of weaned juvenile Atlantic bluefin tuna (Thunnus thynnus L.): effects of dietary lipid level and source

Abstract

Two trials were performed using extruded diets as on-growing feeds for weaned Atlantic bluefin tuna ( Thunnus thynnus ; ABT) to establish adequate dietary levels of both lipid and omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), and impacts on lipid metabolism via liver gene expression. In trial A, ABT were fed with either a commercial feed (Magokoro®; MGK) as a reference diet or two experimental feeds differing in lipid levels (15 or 20%) using krill oil (KO) as the single lipid source in order to estimate suitable lipid content. Fish fed MGK displayed the highest growth, followed by 15KO, and therefore a dietary lipid content of 15% was considered preferable to 20% at this stage. In trial B, fish were fed MGK, 15KO, or a feed containing 15% lipid with a blend of KO and rapeseed oil (RO) (1:1, v / v ; 15KORO). Fish fed 15KO and 15KORO showed no difference in weight gain, specific growth rate, and fork length. Increasing dietary lipid level or including vegetable oil, RO, in the feeds did not increase liver lipid content. Liver fatty acid compositions largely reflected dietary profiles confirming very limited endogenous LC-PUFA biosynthesis. Liver of ABT fed 15KO and 20KO displayed the highest contents of docosahexaenoic acid (DHA). The hepatic expression of genes encoding enzymes and transcription factors involved in lipid and fatty acid metabolism, as well as genes encoding antioxidant enzymes, showed that many of these genes were regulated by dietary lipid and LC-PUFA content. Results suggested that ABT juveniles can be on-grown on inert dry feeds that support good fish growth and the accumulation of DHA. Electronic supplementary material The online version of this article (10.1007/s10695-018-0587-9) contains supplementary material, which is available to authorized users.

Molecular and functional characterisation of a putative elovl4 gene and its expression in response to dietary fatty acid profile in Atlantic bluefin tuna (Thunnus thynnus)

“…Traditionally, ABT fisheries have been supplemented by farming although this has actually relied on the capture of juveniles in the wild, to be fattened in so-called tuna ranches (Benetti et al, 2016). In recent years, considerable efforts have been made to close the life cycle of ABT (van Beijnen, 2017), and success in the production of larvae and juveniles has provided the animals to enable studies into the elucidation of ideal compositions of both live feeds (Betancor et al, 2017a,b) and inert weaning diets (Betancor et al, 2019). Compared to most teleost fish species, tissues of ABT have high levels of the health-beneficial omega-3 long-chain (C20-24) polyunsaturated fatty acid (n-3 LC-PUFA), docosahexaenoic acid (DHA; 22:6n-3) and very high DHA: eicosapentaenoic acid (EPA; 20:5n-3) ratios Tocher, 2003, 2009).…”

Rhythmic expressions of biological clocks and metabolic genes in marine medaka ( Oryzias melastigma )

“…The Srebp1 transcription factor also reached its peak at the beginning and mid of the photoperiod, and its target genes Fadsd2 and Elovl5 showed obvious daily rhythm in treatment 2#. In bony fish, the expression levels of Fadsd2 or Elovl5 were affected by dietary lipid content and fatty acid profile (Betancor et al, 2015, 2019; Thomassen et al, 2012), which indicated that the difference of feed nutrition level would also affect the expression of metabolic genes, but whether it will affect the influence of peripheral clock genes still needed further study. Moreover, Fadsd2 did not show obvious daily rhythm in treatment 1#, indicating that the photoperiod may also affect the expression of metabolic genes.…”

Central and peripheral clocks in Atlantic bluefin tuna (Thunnus thynnus, L.): Daily rhythmicity of hepatic lipid metabolism and digestive genes

“…It should be noted that, in teleosts, the expression levels of fads2 or elovl5 are affected by dietary lipid content and/or fatty acid profiles (Thomassen et al, 2012;Betancor et al, 2015Betancor et al, , 2019 and, therefore, the presence/lack of rhythmicity observed in the different studies might be related to variations in dietary levels of these essential nutrients. In the case of ABT, this might be key given that, firstly, requirements of LC-PUFA for this species have not yet been accurately determined and, secondly, ABT are top predators known to possess very limited elovl5 activity (Morais et al, 2011;Betancor et al, 2019). On the other hand, Lxr, a nuclear receptor that regulates the metabolism of several important lipids and is known to activate the transcription of srebp genes (Schultz et al, 2000) exhibited a diurnal rhythm, achieving its zenith at ~ ZT3.…”