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[EN] Different strategies have been followed to improve the aquaculture of main European farmed fish, such as genetic selection, refinements in culture conditions or enhanced feed formulation and management. However, more knowledge is required to exploit fish phenotypic plasticity to obtain those that better match aquaculture or market conditions. The overall objective of this mini-review is to identify the latest productive traits recently performed, mainly in commercial carnivorous species, and underlying biological processes that would be susceptible to improve the competitivity of aquaculture sector through nutritional issues. Thus, this work is framed within the concepts of Circular Economy and Blue Growth, where it is intended to point out the use of natural compounds extracted from seaweeds, microalgae and by-products of the industry for their inclusion in aquafeeds, allowing a more efficient use of more sustainable vegetable protein sources, and also to evaluate if these nutraceutical compounds counteract detrimental effects observed by nutritional interventions or environmentally challenged., [ES] La producción acuícola ha seguido diferentes estrategias para su optimización a lo largo de las últimas décadas, como el desarrollo de la selección genética, la mejora de las condiciones de cultivo, o el avance en la formulación y gestión de los piensos. Sin embargo, se requiere más conocimiento para explotar la plasticidad fenotípica de los peces para obtener aquellos que se ajusten mejor a las condiciones de la acuicultura o del mercado. El objetivo general de esta mini-revisión es identificar los últimos avances realizados recientemente, principalmente en especies carnívoras comerciales, y los procesos biológicos subyacentes que serían susceptibles de mejorar la competitividad del sector acuícola a través de intervenciones nutricionales. Así, este trabajo se enmarca dentro de los conceptos de Economía Circular y Crecimiento Azul, donde se pretende señalar el uso de compuestos naturales extraídos de algas, microalgas y subproductos de la industria para su inclusión en alimentos acuícolas, permitiendo un uso más eficiente de fuentes de proteínas vegetales más sostenibles, y también evaluar si estos compuestos nutracéuticos son capaces de contrarrestar los efectos perjudiciales observados por las formulaciones inadecuadas o desafiados por factores ambientales estresantes.

[EN] Aquaculture is the best bet for the future to face the great challenge of providing food to a population that will reach 9 billion people in 2050. However, to increase the production performance of aquaculture in a sustainable way, it is necessary to develop strategies, such as species diversification or the use of more sustainable diets. In this respect, the greater amberjack (Seriola dumerili) is a good candidate both for its high biological and economic potential. However, as a carnivorous species, it has high protein requirements, most of which from fish meal. Therefore, it is essential to replace ingredients of animal origin with more sustainable ones such as plant raw materials. However, diets with a high content of vegetable ingredients can affect the bioavailability and digestibility of nutrients causing negative effects on fish growth and health. Nevertheless, the use of biotechnological pretreatments of plant ingredients and the inclusion of nutraceutical compounds have allowed to improve the use of these nutrients, providing good growth and health status of a highly carnivorous species such as greater amberjack., [ES] La acuicultura es la mejor apuesta de futuro para hacer frente al gran desafío de proporcionar alimentos a una población que superará los 9 billones de personas en 2050. Sin embargo, para incrementar el rendimiento de la producción acuícola de manera sostenible es necesario desarrollar estrategias como la diversificación de especies o el uso de dietas más sostenibles. En este sentido, la seriola o pez limón (Seriola dumerili), es un buen candidato tanto por su gran potencial biológico como económico. Sin embargo, como especie carnívora, presenta unos altos requerimientos de proteínas, procedentes la mayor parte de las harinas de pescado. Por tanto, es imprescindible la sustitución de ingredientes de origen animal por otros más sostenibles como las materias primas vegetales. Aun así, dietas con un alto contenido de ingredientes vegetales pueden afectar a la biodisponibilidad y digestibilidad de los nutrientes causando efectos negativos sobre el crecimiento y la salud de los peces. Sin embargo, el uso de pretratamientos biotecnológicos de los ingredientes vegetales y la inclusión de compuestos nutraceúticos han permitido un buen uso de los nutrientes presentes en estas dietas, proporcionando un buen crecimiento y estado de salud en una especie altamente carnívora como la seriola.

The present study evaluated, in an 18-month gilthead sea bream trial, the time course effects of genetics on individual size variation and growth compensation processes in the offspring of families selected by growth in the PROGENSA breeding program. Families categorized as fast, intermediate and slow growing had different growth trajectories with a more continuous growth in fast growth families. This feature was coincident with a reduced size variation at the beginning of the trial that clustered together the half-sib families sharing the same father. Correlation analysis evidenced that the magnitude of compensatory growth was proportional to the initial size variation with no rescaling of families at this stage. By contrast, the finishing growth depensation process can mask, at least partially, the previous family convergence. This reflects the different contribution across the production cycle of genetics and environmental factors in growth, production and welfare. How early life experiences affect growth compensatory at juvenile stages was also evaluated in a separate cohort, and intriguingly, a first mild-hypoxia pulse at 60-81 days posthatching (dph) increased survival rates by 10% preventing growth impairment when fish were exposed to a second hypoxia episode (112-127 dph). The early hypoxia experience did not have a negative impact on growth compensatory processes at juvenile stages. By contrast, a diminished capacity for growth compensation was found with repeated or late hypoxia experiences. All this reinforces the use of size variation as a main criterion for improving intensive fish farming or selective breeding into practice.

High substitution of fish oil (FO) by vegetable oils (VO) in aquafeeds is still a challenge for marine fish. VOs have low content of n-3 LC-PUFA such as EPA and DHA, and instead, they are rich in fatty acids (FA) such as ALA and LA. High VO feeding leads to increased hepatic fat accumulation in gilthead sea bream (Sparus aurata) and other fish species, increasing the risk of steatosis. Different studies in fish have provided evidence of the effect of broodstock nutrition on the lipid metabolism of the progeny (e.g., Izquierdo et al., 2015; Turkmen et al., 2017). In higher vertebrates, enriching maternal diet with ALA prevented fatty liver in the offspring (Hollander et al., 2014) by decreasing both SCD1 and FADS2 gene expression (Leikin-Frenkel et al., 2017). We used a ‘control’ and an ‘ALA-rich’ diet to study the effect of parent’s nutrition on the promoter methylation and gene expression of fads2 and scd1a in S. aurata offspring.

Three gilthead sea bream families representative of slow, intermediate and fast heritable growth in the Spanish PROGENSA (R) selection program were used to uncover the effects of such selection on energy partitioning through measurements of fasting weight loss, swimming performance and behavioral traits in one- and two-year-old fish. Firstly, selection for fast growth significantly increased fasting weight loss and decreased the hormonal ratio of circulating Igf-i/Gh in short-term fasting fish (17 days). This is indicative of a stronger negative energy balance that explains the reduced compensatory growth of fast-growing fish during the subsequent short-term refeeding period (7 days). Selection for fast growth also decreased the critical speed (Ucrit, 6-7 BL sxfffd; 1) at which fish become exhausted in a swim tunnel respirometer. The maximum metabolic rate (MMR), defined as the maximum rate of oxygen consumption during forced exercise, was almost equal in all fish families though the peak was achieved at a lowest speed in the fast-growing family. Since circulating levels of lactate were also slightly decreased in freeswimming fish of this family group, it appears likely that the relative energy contribution of anaerobic metabolism to physical activity was lowered in genetically fast-growing fish. Selection for heritable growth also altered activity behavior because slow-growing families displayed an anticipatory food response associated with more pronounced daily rhythms of physical activity. Also, respiratory frequency and body weight showed and opposite correlation in slow- and fast-growing free-swimming fish as part of the complex trade-offs of growth, behavior and energy metabolism. Altogether, these results indicate that selective breeding for fast growth might limit the anaerobic fitness that would help to cope with limited oxygen availability in a scenario of climate change.

A customized PCR-array of 28 selected genes was used for assessing the simultaneous expression of the Gh/Igf system and related markers of muscle growth, and lipid and energy metabolism during early life stages of gilthead sea bream (60-127 days posthatching). Also, transcriptional reprogramming by mild hypoxia was assessed in fingerling fish with different history trajectories on O2 availability during the same time window. In normoxic fish, the expression of almost all the genes in the array varied over time with a prompted liver and muscle tissue-specific differentiation, which revealed temporal changes in the relative expression of markers of the full gilthead sea bream repertoire of Gh receptors, Igfs and Igf-binding proteins. Results supported a different contribution through development of ghr and igf subtypes on the type of action of GH via systemic or direct effects at the local tissue level. This was extensive to Igfbp1/2/4 and Igfbp3/5/6 clades that clearly evolved through development as hepatic and muscle Igfbp subtypes, respectively. This trade-off is however very plastic to cope changes in the environment, and ghr1 and igfbp1/3/4/5 emerged as hypoxic imprinting genes during critical early developmental windows leading to recognize individuals with different history trajectories of O2 availability and metabolic capabilities later in life. How this knowledge can contribute to establish robust criteria of larval and juvenile fish quality requires more research, though changes in the expression and the quotient expression ratio of duplicated ghr/igf/ igfbp genes can serve as a measure of developmental progression and metabolic disturbances of the offspring. Besides, growth, health and well-being also depend on the daily synchronization of endogenous biological rhythms, and the expression of selected genes from antiphase clusters can serve to find synchrony indicators of gilthead sea bream during early life.

On-growing juveniles of gilthead sea bream were acclimated for 45 days to mild-hypoxia (M-HYP, 40–60% O2 saturation), whereas normoxic fish (85–90% O2 saturation) constituted two different groups, depending on if they were fed to visual satiety (control fish) or pair-fed to M-HYP fish. Following the hypoxia conditioning period, all fish were maintained in normoxia and continued to be fed until visual satiation for 3 weeks. The time course of hypoxia-induced changes was assessed by changes in blood metabolic landmarks and muscle transcriptomics before and after exhaustive exercise in a swim tunnel respirometer. In M-HYP fish, our results highlighted a higher contribution of aerobic metabolism to whole energy supply, shifting towards a higher anaerobic fitness following normoxia restoration. Despite these changes in substrate preference, M-HYP fish shared a persistent improvement in swimming performance with a higher critical speed at exercise exhaustion. The machinery of muscle contraction and protein synthesis and breakdown was also largely altered by mild-hypoxia conditioning, contributing this metabolic re-adjustment to the positive regulation of locomotion and to the catch-up growth response during the normoxia recovery period. Altogether, these results reinforce the presence of large phenotypic plasticity in gilthead sea bream, and highlights mild-hypoxia as a promising prophylactic measure to prepare these fish for predictable stressful events.

A customized PCR-array was used for the simultaneous gene expression of the Gh/Igf system and related markers of muscle growth, and lipid and energy metabolism during early life stages of gilthead sea bream (60–127 days posthatching). Also, transcriptional reprogramming by mild hypoxia was assessed in fingerling fish with different history trajectories on O availability during the same time window. In normoxic fish, the expression of almost all the genes in the array varied over time with a prompted liver and muscle tissue-specific differentiation, which also revealed temporal changes in the relative expression of markers of the full gilthead sea bream repertoire of Gh receptors, Igfs and Igf-binding proteins. Results supported a different contribution through development of ghr and igf subtypes on the type of action of GH via systemic or direct effects at the local tissue level. This was extensive to Igfbp1/2/4 and Igfbp3/5/6 clades that clearly evolved through development as hepatic and muscle Igfbp subtypes, respectively. This trade-off is however very plastic to cope changes in the environment, and ghr1 and igfbp1/3/4/5 emerged as hypoxic imprinting genes during critical early developmental windows leading to recognize individuals with different history trajectories of oxygen availability and metabolic capabilities later in life.

Three gilthead sea bream families representative of slow, intermediate and fast heritable growth in the Spanish PROGENSA® selection program were used to uncover the effects of such selection on energy partitioning through measurements of fasting weight loss, swimming performance and behavioral traits in one- and two-year-old fish. Firstly, selection for fast growth significantly increased fasting weight loss and decreased the hormonal ratio of circulating Igf-i/Gh in short-term fasting fish (17 days). This is indicative of a stronger negative energy balance that explains the reduced compensatory growth of fast-growing fish during the subsequent short-term refeeding period (7 days). Selection for fast growth also decreased the critical speed (Ucrit, 6–7 BL s−1) at which fish become exhausted in a swim tunnel respirometer. The maximum metabolic rate (MMR), defined as the maximum rate of oxygen consumption during forced exercise, was almost equal in all fish families though the peak was achieved at a lowest speed in the fast-growing family. Since circulating levels of lactate were also slightly decreased in free-swimming fish of this family group, it appears likely that the relative energy contribution of anaerobic metabolism to physical activity was lowered in genetically fast-growing fish. Selection for heritable growth also altered activity behavior because slow-growing families displayed an anticipatory food response associated with more pronounced daily rhythms of physical activity. Also, respiratory frequency and body weight showed and opposite correlation in slow- and fast-growing free-swimming fish as part of the complex trade-offs of growth, behavior and energy metabolism. Altogether, these results indicate that selective breeding for fast growth might limit the anaerobic fitness that would help to cope with limited oxygen availability in a scenario of climate change.

Farmed gilthead sea bream (Sparus aurata) is able to grow efficiently with new feed formulations based on plant ingredients. Here, two experimental diets with standard and high inclusion levels of plant ingredients were formulated to assess the suited use of plant-based diets in fish with different growth genetic backgrounds. To pursue this issue, a long-term feeding trial (12-months) was conducted with fish (17 g initial body weight) of 16 families coming from the broodstock of PROGENSA project, that were grown communally in the IATS-CSIC experimental facilities. All fish in the study (2545) were PIT-tagged, and their pedigree was re-constructed with 96% success by using a SMsa1 multiplex of 11 microsatellites, which revealed the main parents contributions of 5 females and 6 males. Each diet was randomly assigned to replicate 3000 L tanks, gathering each replicate a similar family composition through all the feeding trial. Data on growth performance highlighted a strong ge- netic effect on growth trajectories, associated with enhanced growth during winter in fish selected for faster growth. No main dietary effects were found on growth rates or condition factor, and regression-correlation analyses of growth rates across families on both diets suggest that genome by diet interaction was weak, while genetic variation accounted for most of the growth phenotypic variation. Hepatosomatic index (HSI) and me- senteric fat index (MSI) of five families, covering the growth variability of the population, were regulated nu- tritionally and genetically, but without statistically significant genome by diet interactions. Fish from faster growing families showed shorter intestines after being fed the control diet, but this phenotype was masked by the enriched plant-based diet. Collectively, the results demonstrate that selection for faster growth is associated in gilthead sea bream with different growth trajectories and a high diet flexibility and intestine plasticity.

Two different O2 levels (normoxia: 75¿85% O2 saturation; moderate hypoxia: 42¿43% O2 saturation) and stocking densities (LD: 9.5, and HD: 19 kg/m3) were assessed on gilthead sea bream (Sparus aurata) in a 3-week feeding trial. Reduced O2 availability had a negative impact on feed intake and growth rates, which was exacerbated by HD despite of the improvement in feed efficiency. Blood physiological hallmarks disclosed the enhancement in O2-carrying capacity in fish maintained under moderate hypoxia. This feature was related to a hypo-metabolic state to cope with a chronic and widespread environmental O2 reduction, which was accompanied by a differential regulation of circulating cortisol and growth hormone levels. Customized PCR-arrays were used for the simultaneous gene expression profiling of 34¿44 selected stress and metabolic markers in liver, white skeletal muscle, heart, and blood cells. The number of differentially expressed genes ranged between 22 and 19 in liver, heart, and white skeletal muscle to 5 in total blood cells. Partial Least-Squares Discriminant Analysis (PLS-DA) explained [R2Y(cum)] and predicted [Q2Y(cum)] up to 95 and 65% of total variance, respectively. The first component (R2Y = 0.2889) gathered fish on the basis of O2 availability, and liver and cardiac genes on the category of energy sensing and oxidative metabolism (cs, hif-1¿, pgc1¿, pgc1ß, sirts 1-2-4-5-6-7), antioxidant defense and tissue repair (prdx5, sod2, mortalin, gpx4, gr, grp-170, and prdx3) and oxidative phosphorylation (nd2, nd5, and coxi) highly contributed to this separation. The second component (R2Y = 0.2927) differentiated normoxic fish at different stocking densities, and the white muscle clearly promoted this separation by a high over-representation of genes related to GH/IGF system (ghr-i, igfbp6b, igfbp5b, insr, igfbp3, and igf-i). The third component (R2Y = 0.2542) discriminated the effect of stocking density in fish exposed to moderate hypoxia by means of hepatic fat

Sirtuins (SIRTs) are a conserved family of enzymes that couple protein deacetylation of histone and non-histone substrates with the energy status of the cell via the cellular NAD+/NADH ratio. This protein family has been largely conserved through evolution, and the SIRT counterparts of higher vertebrates have been identified and molecularly characterized in gilthead sea bream (Simó-Mirabet et al., 2017). Transcriptional studies have also revealed a ubiquitous sirt gene expression that is tissue-specific for each sirt and highly dependent on feed intake and growth potentiality (Simó-Mirabet et al., 2017, 2018). This agrees with an epigenetic role of SIRT related with developmental, differentiation and genome environment interactions. Nevertheless, there are few studies assessing the DNA methylation pattern of SIRT promoters, and the aim of this study was to determine if changes of sirt gene expression in liver and white skeletal muscle of one- and three-year old fish during winter and summer are due, at least in part, to changes in DNA methylation of sirt promoters. The study also included the gene expression profilingof markers of oxidative metabolism (cs, cpt1a, pgc1a) and mitochondrial respiration uncoupling (ucp1, ucp3). The exon-intron organization of the seven gilthead seabream sirts was determined by blat searches in our genomic gilthead sea bream database (http://nutrigroup-iats.org/seabreamdb). This in silico analysis included predictions of transcription start sites (TSS), core promoter regions, transcription factor binding sites (TFBS) and CpG islands (CGIs). For transcriptional and DNA methylation assays, tissue portions of liver and white skeletal muscle were processed for RNA and DNA extraction in fish of two class of age (+1, +3) at two different times (winter, February 2018; summer, June 2018). DNA methylation was examined by bisulfite conversion and pyrosequencing of CGIs close to TSS of sirt1 (22 CpG sites) and sirt3 (4 CpG sites). Gene expression p

The gilthead sea bream (Sparus aurata) is an euryhaline teleost species with an unmatched capacity for osmoregulatory adaptation. Moreover, environmental salinities that differ from the internal milieu produce a great energetic cost to regulate active ion transport. The present study evaluates, in an 11-weeks feeding trial using a RAS system, the effect of three different environmental salinities (brackish water, BW: 18 ppt; seawater, SW: 37 ppt; and high salinity water, HSW: 55 ppt) on osmoregulatory capacity, growth performance, stress processes and metabolism in S. aurata juveniles (~7 g initial mean body mass). Plasma osmolality did not show significant differences among the three experimental groups, demonstrating the good osmoregulatory acclimation of fish despite the wide range of environmental osmolalities assayed (500-1720 mOsm/kg). Even so, the metabolic orchestration related to glucose, triglycerides and lactate confirms a clear energy repartitioning at hepatic and muscular levels, indicating that the higher energy budget invested for osmoregulatory function produces a salinity-dependent reduction in growth-related parameters. In this regard, BW-acclimated fish enhanced feed intake and feed efficiency when compared to fish kept under hyperosmotic (SW and HSW) environments, which is translated into better growth rates. All these features can be attributed to a shorter (BW < SW ¿ HSW) but more specific intestine for nutritional purposes. Finally, important stress-related markers at hypothalamic (corticotrophin releasing hormone, crh binding protein), hypophyseal (proopiomelanocortin a and b) and plasma (cortisol) levels will be unraveled as putative endocrine mediators of the metabolic and osmoregulatory capacity of acclimated fish

Two different O2 levels (normoxia: 75¿85% O2 saturation; moderate hypoxia: 42¿43% O2 saturation) and stocking densities (LD: 9.5, and HD: 19 kg/m3) were assessed on gilthead sea bream (Sparus aurata) in a 3-week feeding trial. Reduced O2 availability had a negative impact on feed intake and growth rates, which was exacerbated by HD despite of the improvement in feed efficiency. Blood physiological hallmarks disclosed the enhancement in O2-carrying capacity in fish maintained under moderate hypoxia. This feature was related to a hypo-metabolic state to cope with a chronic and widespread environmental O2 reduction, which was accompanied by a differential regulation of circulating cortisol and growth hormone levels. Customized PCR-arrays were used for the simultaneous gene expression profiling of 34¿44 selected stress and metabolic markers in liver, white skeletal muscle, heart, and blood cells. The number of differentially expressed genes ranged between 22 and 19 in liver, heart, and white skeletal muscle to 5 in total blood cells. Partial Least-Squares Discriminant Analysis (PLS-DA) explained [R2Y(cum)] and predicted [Q2Y(cum)] up to 95 and 65% of total variance, respectively. The first component (R2Y = 0.2889) gathered fish on the basis of O2 availability, and liver and cardiac genes on the category of energy sensing and oxidative metabolism (cs, hif-1¿, pgc1¿, pgc1ß, sirts 1-2-4-5-6-7), antioxidant defense and tissue repair (prdx5, sod2, mortalin, gpx4, gr, grp-170, and prdx3) and oxidative phosphorylation (nd2, nd5, and coxi) highly contributed to this separation. The second component (R2Y = 0.2927) differentiated normoxic fish at different stocking densities, and the white muscle clearly promoted this separation by a high over-representation of genes related to GH/IGF system (ghr-i, igfbp6b, igfbp5b, insr, igfbp3, and igf-i). The third component (R2Y = 0.2542) discriminated the effect of stocking density in fish exposed to moderate hypoxia by means of hepatic fat

Intestinal microbiota is key for many host functions, such as digestion, nutrient metabolism and absorption, disease resistance and immune function. With the growth of the aquaculture industry, there has been a growing interest in the manipulation of fish gut microbiota to improve welfare and nutrition (Egerton et al., 2018). However, a long road lies ahead to establish the baseline parameters to guide this manipulation. Intestinal microbiota varies with many factors, including host species, genetics, developmental stage, diet, environment and sex. The aim of this study was to compare the intestinal microbiota of adult gilthead sea bream (GSB, Sparus aurata) from three groups of age maintained under the same conditions.

Intestinal microbiota is key for many host functions, such as digestion, nutrient metabolism and absorption, disease resistance and immune function. With the growth of the aquaculture industry, there has been a growing interest in the manipulation of fish gut microbiota to improve welfare and nutrition (Egerton et al., 2018). However, a long road lies ahead to establish the baseline parameters to guide this manipulation. Intestinal microbiota varies with many factors, including host species, genetics, developmental stage, diet, environment and sex. The aim of this study was to compare the intestinal microbiota of adult gilthead sea bream (GSB, Sparus aurata) from three groups of age maintained under the same conditions. One-, 2- and 4-year old GSB (Y+1, Y+2, Y+4) were kept in the same open-flow system and fed the same diet for more than 6 months. After 2-days of fasting, 10 fish per group were sacrificed and the anterior intestinal portion was dissected, opened and washed to remove non-adherent bacteria. Intestinal mucus was scrapped off and immediately used for DNA extraction. The V3-V4 region of the 16S rRNA of each individual sample was amplified and sequenced by Illumina MiSeq. All Y+1 individuals were males, while the ones belonging to Y+2 and Y+4 age classes were females. A total of 686461 high quality reads (22882/sample) were assigned to 846 OTUs (97% identity). Almost 30% of the OTUs were classifiedup to the level of species. Microbiota diversity and richness did not differ among age groups; however bacterial composition did , highlighting the presence of Photobacterium and Vibrio only after 2 years of age and a higher presence of Staphylococcusand Corynebacterium in Y+1 animals. The core microbiota was defined by 14 OTUs and the groups that showed more OTUs in common were Y+2 and Y+4. PLS-DA analysis showed a clear separation by sex (component 1) and age (component 2), with bacteria belonging to the phyla Firmicutes, Proteobacteria and Actinobacteria drivi

Polyunsaturated fatty acids (PUFA) in parental diets play a key role in regulating n-3 LC-PUFA metabolism of the offspring. However, it is not clear whether this metabolic regulation is driven by the precursors presented in the diet or by the parental ability to synthesize them. To elucidate this, broodstocks of gilthead sea bream with different blood expression levels of fads2, which encodes for the rate-limiting enzyme in the n-3 LC-PUFA synthesis pathway, were fed either a diet supplemented with alpha-linolenic acid (ALA, 18:3n-3) or a control diet. The progenies obtained from these four experimental groups were then challenged with a low LC-PUFA diet at the juvenile stage. Results showed that the offspring from parents with high fads2 expression presented higher growth and improved utilization of low n-3 LC-PUFA diets compared to the offspring from parents with low fads2 expression. Besides, an ALA-rich diet during the gametogenesis caused negative effects on the growth of the offspring. The epigenetic analysis demonstrated that methylation in the promoter of fads2 of the offspring was correlated with the parental fads2 expression levels and type of the broodstock diet.

Farmed gilthead sea bream (Sparus aurata) is able to grow efficiently with new feed formulations based on plant ingredients. Here, two experimental diets with standard and high inclusion levels of plant ingredients were formulated to assess the suited use of plant-based diets in fish with different growth genetic backgrounds. To pursue this issue, a long-term feeding trial (12-months) was conducted with fish (17 g initial body weight) of 16 families coming from the broodstock of PROGENSA project, that were grown communally in the IATS-CSIC experimental facilities. All fish in the study (2545) were PIT-tagged, and their pedigree was re-constructed with 96% success by using a SMsa1 multiplex of 11 microsatellites, which revealed the main parents contributions of 5 females and 6 males. Each diet was randomly assigned to replicate 3000 L tanks, gathering each replicate a similar family composition through all the feeding trial. Data on growth performance highlighted a strong genetic effect on growth trajectories, associated with enhanced growth during winter in fish selected for faster growth. No main dietary effects were found on growth rates or condition factor, and regression-correlation analyses of growth rates across families on both diets suggest that genome by diet interaction was weak, while genetic variation accounted for most of the growth phenotypic variation. Hepatosomatic index (HSI) and mesenteric fat index (MSI) of five families, covering the growth variability of the population, were regulated nutritionally and genetically, but without statistically significant genome by diet interactions. Fish from faster growing families showed shorter intestines after being fed the control diet, but this phenotype was masked by the enriched plant-based diet. Collectively, the results demonstrate that selection for faster growth is associated in gilthead sea bream with different growth trajectories and a high diet flexibility and intestine plasticity.