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Selection for high growth improves reproductive performance of gilthead seabream Sparus aurata under mass spawning conditions, regardless of the dietary lipid source
Abstract
Genetic selection programmes in gilthead seabream mainly focus on traits related to growth, disease resistance, skeletal anomalies, or fillet quality. However, the effect of selection for growth on the reproductive performance of seabream broodstock has not received much attention. The present study aimed to determine the effect of selection for growth traits, high (HG) or low (LG) growth, and broodstock feeding with fish oil (FO diet) or rapeseed oil (RO diet) as main lipid sources, on reproductive performance of gilthead seabream. For the first part of the spawning season (Phase I) HG and LG broodstock were fed a commercial diet and the HG broodstock produced a higher number of larvae and higher viable eggs, hatching and larval survival rates than LG broodstock, affecting egg fatty acid profiles. For the second part of the study (Phase II) broodstock were fed one of the two diets containing FO or RO. Fecundity in terms of viable eggs, hatchlings, and larvae produced, as well as fertilization rates, were improved in HG broodstock. Some fatty acids such as 18:0, 20:2n-6, 20:3n-3 or EPA/ARA were also affected by the growth selection. According to the two-way ANOVA analysis, feeding the RO diet did not significantly affect fecundity parameters, but slightly reduced fertilization and hatching rates in HG broodstock. Nevertheless, HG broodstock showed better spawning quality parameters than LG broodstock, even when they were fed the RO diet. Egg fatty acid profiles reflected diet composition, although DHA contents were not affected. In conclusion, broodstock selected for high growth had a positive effect on broodstock performance, and FO replacement by RO did not markedly affect reproduction providing that fatty acid contents were sufficient to fulfil the essential fatty acid requirements of gilthead seabream broodstock.
... Lipid is a key factor affecting the reproductive performance of animals (Nzohabonayo et al. 2017;Shajahan et al. 2022). Many studies have revealed the roles of n-3 LC-PUFA fatty acids (DHA and EPA) in oocyte maturation, spawning, and hatching success of fish (Asil et al. 2017;Harlioğlu et al. 2012), but little research has investigated the impacts of mediumchain fatty acids (C6 ~ C12) on reproduction in fish. ...
This study aims to explore whether glycerol monolaurate (GML) can improve reproductive performance of female zebrafish (Danio rerio) and the survival percentage of their offspring. Three kinds of isonitrogenous and isolipid diets, including basal diet (control) and basal diet containing 0.75 g/kg GML (L_GML) and 1.5 g/kg GML (H_GML), were prepared for 4 weeks feeding trial. The results show that GML increased the GSI of female zebrafish. GML also enhanced reproductive performance of female zebrafish. Specifically, GML increased spawning number and hatching rate of female zebrafish. Moreover, GML significantly increased the levels of triglycerides (TG), lauric acid, and estradiol (E2) in the ovary (P < 0.05). Follicle-stimulating hormone (FSH) levels in the ovary and brain also significantly increased in the L_GML group (P < 0.05). Besides, dietary GML regulated the hypothalamus-pituitary-gonad (HPG) axis evidenced by the changed expression levels of HPG axis-related genes in the brain and ovary of the L_GML and H_GML groups compared with the control group. Furthermore, compared with the control group, the expression levels of HPG axis-related genes (kiss2, kiss1r, kiss2r, gnrh3, gnrhr1, gnrhr3, lhβ, and esr2b) in the brain of the L_GML group were significantly increased (P < 0.05), and the expression levels of HPG axis-related genes (kiss1, kiss2, kiss2r, gnrh2, gnrh3, gnrhr4, fshβ, lhβ, esr1, esr2a, and esr2b) in the brain of the H_GML group were significantly increased (P < 0.05). These results suggest that GML may stimulate the expression of gnrh2 and gnrh3 by increasing the expression level of kiss1 and kiss2 genes in the hypothalamus, thus promoting the synthesis of FSH and E2. The expression levels of genes associated with gonadotropin receptors (fshr and lhr) and gonadal steroid hormone synthesis (cyp11a1, cyp17, and cyp19a) in the ovary were also significantly upregulated by dietary GML (P < 0.05). The increasing expression level of cyp19a also may promote the FSH synthesis. Particularly, GML enhanced the richness and diversity and regulated the species composition of intestinal microbiota in female zebrafish. Changes in certain intestinal microorganisms may be related to the expression of certain genes involved in the HPG axis. In addition, L_GML and H_GML both significantly decreased larvae mortality at 96 h post fertilization and their mortality during the first-feeding period (P < 0.05), revealing the enhanced the starvation tolerance of zebrafish larvae. In summary, dietary GML regulated genes related to HPG axis to promote the synthesis of E2 and FSH and altered gut microbiota in female zebrafish, and improved the survival percentage of their offspring.
... Furthermore, the presence of skeletal anomalies negatively impacts the well-being of the fish, as deformed fish can be more susceptible to parasites (i.e., when opercular reductions are present) or feed less effectively (if affected by severe anomalies in the jaws or vertebral column). The zootechnical approaches aimed at increasing production quantity have led researchers to investigate the effects of genetic variability and fitness, inbreeding, selective breeding of desired quantitative traits (Afonso et al., 2000;Berillis, 2017;Fragkoulis et al., 2018Fragkoulis et al., , 2020, proper nutritional requirements (Baeverfjord et al., 2019;Cahu et al., 2003;Darias et al., 2011;Dominguez et al., 2021Dominguez et al., , 2022Ferosekhan et al., 2022;Georga et al., 2011;Izquierdo et al., 2017Izquierdo et al., , 2019Lall & Lewis-McCrea, 2007;Sivagurunathan et al., 2022;Tseng et al., 2021); and the use of superficial skimmers (Chatain & Ounais-Guschemann, 1990), on growth and skeletal quality (viz. targeting to reduce the incidence of skeletal anomalies). ...
This study describes the effects on the skeletal phenotype of two pivotal factors, density and water volume, don the hatchery (larval) phase of gilthead seabream (Sparus aurata) larvae previoulsy described for two model species (Danio rerio and Oryzias latipes) and sub-adult (pre-ongrowing) gil-thead seabream (Sparus aurata). The experimental trial was conducted using single conditions in a pilot study, starting with a total of 615,385 eggs from the same batch. Three densities (LD low density: 25 larvae/L; MD medium density: 125 larvae/L; and HD high density: 250 larvae/L) and two water volumes (500 and 1000 L) were tested from spawning
... Ingredients and composition of the broodstock diet are given in Additional file 8: Supplementary Table 5. Eggs were collected at spawning from the two broodstocks and the offsprings were reared under standard conditions for approximately 5 months (intermediate phase). For further details on the broodstock diet and the spawning quality please see Ferosekhan et al. [89]. Naya-Català et al. ...
Background
Broodstock nutritional programming improves the offspring utilization of plant-based diets in gilthead sea bream through changes in hepatic metabolism. Attention was initially focused on fatty acid desaturases, but it can involve a wide range of processes that remain largely unexplored. How all this can be driven by a different genetic background is hardly underlined, and the present study aimed to assess how broodstock nutrition affects differentially the transcriptome and genome-wide DNA methylome of reference and genetically selected fish within the PROGENSA® selection program.
Results
After the stimulus phase with a low fish oil diet, two offspring subsets of each genetic background received a control or a FUTURE-based diet. This highlighted a different hepatic transcriptome (RNA-seq) and genome-wide DNA methylation (MBD-seq) pattern depending on the genetic background. The number of differentially expressed transcripts following the challenge phase varied from 323 in reference fish to 2,009 in genetically selected fish. The number of discriminant transcripts, and associated enriched functions, were also markedly higher in selected fish. Moreover, correlation analysis depicted a hyper-methylated and down-regulated gene expression state in selected fish with the FUTURE diet, whereas the opposite pattern appeared in reference fish. After filtering for highly represented functions in selected fish, 115 epigenetic markers were retrieved in this group. Among them, lipid metabolism genes (23) were the most reactive following ordering by fold-change in expression, rendering a final list of 10 top markers with a key role on hepatic lipogenesis and fatty acid metabolism (cd36, pitpna, cidea, fasn, g6pd, lipt1, scd1a, acsbg2, acsl14, acsbg2).
Conclusions
Gene expression profiles and methylation signatures were dependent on genetic background in our experimental model. Such assumption affected the magnitude, but also the type and direction of change. Thus, the resulting epigenetic clock of reference fish might depict an older phenotype with a lower methylation for the epigenetically responsive genes with a negative methylation-expression pattern. Therefore, epigenetic markers will be specific of each genetic lineage, serving the broodstock programming in our selected fish to prevent and mitigate later in life the risk of hepatic steatosis through changes in hepatic lipogenesis and fatty acid metabolism.
... Presently, many studies have been conducted to improve skeletal quality and reduce the presence of skeletal anomalies in gilthead seabream by using tailored rearing strategies to target life-stage specific requirements. Previous works among the main branches of research have focused their efforts on investigating the influence of dietary/nutritional factors [18][19][20][21][22][23][24], genetic components [25][26][27], and environmental dynamics [28][29][30][31][32] on the development of anomalies. ...
Gilthead seabream (Sparus aurata) production is a highly valued aquaculture industry in Europe. The presence of skeletal deformities in farmed gilthead seabream represents a major bottleneck for the industry leading to economic losses, negative impacts on the consumers’ perception of aquaculture, and animal welfare issues for the fish. Although past work has primarily focused on the hatchery phase to reduce the incidence of skeletal anomalies, this work targets the successive pre-ongrowing phase in which more severe anomalies affecting the external shape often arise. This work aimed to test the effects of: (i) larger and smaller tank volumes, stocked at the same density; and (ii) higher and lower stocking densities maintained in the same water volume, on the skeleton of gilthead seabream fingerlings reared for ~63 days at a pilot scale. Experimental rearing was conducted with gilthead seabream juveniles (~6.7 ± 2.5 g), which were selected as ‘non-deformed’ based on external inspection, stocked at three different densities (Low Density (LD): 5 kg/m3; Medium Density (MD): 10 kg/m3; High Density (HD): 20 kg/m3) in both 500 L and 1000 L tanks. Gilthead seabream were sampled for growth performance and radiographed to assess the skeletal elements at the beginning and end of the experimental trial. Results revealed that (i) LD fish were significantly longer than HD fish, although there were no differences in final weights, regardless of the water volume; (ii) an increase in the prevalence of seabream exhibiting cranial and vertebral axis anomalies was found to be associated with increased density. These results suggest that farmers can significantly reduce the presence of some cranial and axis anomalies affecting pre-ongrown gilthead seabream by reducing the stocking density.
Genetic interventions hold immense promise as a transformative tool in addressing global hunger and advancing food security through the enhancement of fisheries. This chapter delves into the convergence of genetics, aquaculture, and food security, unraveling the potential of genetic interventions to revolutionize fisheries into a potent and sustainable source of nutrition. Through an extensive exploration of selective breeding, advanced genetic technologies, and innovative genetic engineering approaches, the chapter illuminates how genetic interventions can elevate the productivity, resilience, and nutritional value of fish populations. Drawing on case studies, ongoing research endeavors, and emerging trends, this chapter provides invaluable insights into the practical applications and implications of genetic interventions for fisheries enhancement on a global scale. Ultimately, it underscores the transformative role of genetic interventions in mitigating hunger, fostering food security, and driving sustainable development, paving the way toward a more equitable and resilient food future for all. Realizing the full potential of fish genetics and breeding programs demands concerted action from policymakers, industry stakeholders, and research communities. Through responsible innovation, collaboration, and knowledge exchange, we can leverage genetics to propel sustainable development and resilience in aquaculture, ensuring the availability of nutritious and sustainable seafood for present and future generations. By advocating for the integration of fish genetics in aquaculture development agendas, highlighting the potential of genetic innovation, and fostering collaboration and knowledge-sharing among diverse stakeholders, we can harness genetics to build a more food-secure, resilient, and sustainable future for upcoming generations.
While the UK is the fourth largest aquaculture producer in Europe by volume, it is the second largest by value with an annual first sale value of around £1 billion. Over 90% of this value is from Atlantic salmon farmed in Scotland, but other fin-fish and shellfish aquaculture species are important to several UK regions. In this review, we describe the state of the art in UK aquaculture breeding and stock supply , and how innovation in genetics technologies can help achieve the Scottish Government's ambitious target of doubling its aquaculture industry by 2030. Particular attention is given to the four most important UK aquaculture species: Atlantic salmon, rainbow trout, blue mussel and Pacific oyster, and we contrast the highly variable level of selective breeding and genomics technologies used in these sectors. A major factor in the success of Atlantic salmon farming has been large-scale investment in modern breeding programmes, including family selection programmes and genomic selection. This has proven cost-effective at scale, leading to improved production efficiency and reduction of some infectious diseases. We discuss the feasibility of applying similar technologies to the UK shellfish sectors, to ensure consistent and robust spat supply and begin trait selection. Furthermore, we discuss species-specific application of modern breeding technologies in a global context, and the future potential of genomics and genome editing technologies to improve commercially desirable traits. Increased adoption of modern breeding technologies will assist UK aquaculture industries to meet the challenges for sustainable expansion, and remain competitive in a global market.
Genetic selection in gilthead seabream (GSB), Sparus aurata, has been undertaken to improve the growth, feed efficiency, fillet quality, skeletal deformities and disease resistance, but no study is available to delineate the effect of genetic selection for growth trait on GSB reproductive performance under mass spawning condition. In this study, high growth (HG) or low growth (LG) GSB broodstock were selected to evaluate the sex steroid hormones, sperm, egg quality and reproductive performance under different feeding regime of commercial diet or experimental broodstock diet containing either fish oil (FO) or vegetable oil (VO) based diet. Under commercial diet feeding phase, broodstock selected for either high growth or low growth did not show any significant changes in the egg production per kg female whereas egg viability percentage was positively (p = 0.014) improved by the high growth trait broodstock group. The experimental diet feeding results revealed that both growth trait and dietary fatty acid composition influenced the reproductive performance of GSB broodstock. In the experimental diet feeding phase, we observed high growth trait GSB males produced a higher number of sperm cells (p < 0.001) and also showed a higher sperm motility (p = 0.048) percentage. The viable egg and larval production per spawn per kg female were significantly improved by the broodstock selected for high growth trait and fed with fish oil-based diet. This present study results signifies that gilthead seabream broodstock selected on growth trait could have positive role in improvement of sperm and egg quality to produce viable progeny.
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.
Background
The key effects of intestinal microbiota in animal health have led to an increasing interest in manipulating these bacterial populations to improve animal welfare. The aquaculture sector is no exception and in the last years, many studies have described these populations in different fish species. However, this is not an easy task, as intestinal microbiota is composed of very dynamic populations that are influenced by different factors, such as diet, environment, host age, and genetics. In the current study, we aimed to determine whether the genetic background of gilthead sea bream (Sparus aurata) influences the intestinal microbial composition, how these bacterial populations are modulated by dietary changes, and the effect of selection by growth on intestinal disease resistance. To that aim, three different groups of five families of gilthead sea bream that were selected during two generations for fast, intermediate, or slow growth (F3 generation) were kept together in the same open-flow tanks and fed a control or a well-balanced plant-based diet during 9 months. Six animals per family and dietary treatment were sacrificed and the adherent bacteria from the anterior intestinal portion were sequenced. In parallel, fish of the fast- and slow-growth groups were infected with the intestinal parasite Enteromyxum leei and the disease signs, prevalence, intensity, and parasite abundance were evaluated.
Results
No differences were detected in alpha diversity indexes among families, and the core bacterial architecture was the prototypical composition of gilthead sea bream intestinal microbiota, indicating no dysbiosis in any of the groups. The plant-based diet significantly changed the microbiota in the intermediate- and slow-growth families, with a much lower effect on the fast-growth group. Interestingly, the smaller changes detected in the fast-growth families potentially accounted for more changes at the metabolic level when compared with the other families. Upon parasitic infection, the fast-growth group showed significantly lower disease signs and parasite intensity and abundance than the slow-growth animals.
Conclusions
These results show a clear genome-metagenome interaction indicating that the fast-growth families harbor a microbiota that is more flexible upon dietary changes. These animals also showed a better ability to cope with intestinal infections.
AtG-AdVb157YBxcFdRtV-VVideo Abstract
Previous studies have shown that it is possible to nutritionally program gilthead seabream offspring through fish oil (FO) replacement by vegetable oils (VO) in the broodstock diet, to improve their ability to grow fast when fed low fish meal (FM) and FO diets during grow-out phase. However, in those studies broodstock performance was reduced by the VO contained diet. Therefore, the present study aimed to determine if it is possible to replace FO by a mixture of FO and rapeseed oil (RO) with a specific fatty acid profile in broodstock diets, without altering gilthead seabream broodstock reproductive performance. Besides, the study also aimed to evaluate the reproductive performance of broodstock with different expression of fatty acid desaturase 2 gene (fads2) a key enzyme in synthesis of long chain polyunsaturated fatty acids. For that purpose, broodfish having either a high (HD) or low (LD) expression of fads2 were fed for three months during the spawning season with two diets containing different fatty acid profiles and their effects on reproductive hormones, fecundity, sperm and egg quality, egg biochemical composition and fads2 expression were studied. The results showed that blood fads2 expression in females, which tended to be higher than in males, was positively related to plasma 17β-estradiol levels. Moreover, broodstock with high blood fads2 expression showed a better reproductive performance, in terms of fecundity and sperm and egg quality, which was correlated with female fads2 expression. Our data also showed that it is feasible to reduce ARA, EPA and DHA down to 0.43, 6.6 and 8.4% total fatty acids, respectively, in broodstock diets designed to induce nutritional programming effects in the offspring without adverse effects on spawning quality. Further studies are being conducted to test the offspring with low FM and FO diets along life span.
Despite carotenoids and essential fatty acids seem to play important roles in fish reproduction, no studies have yet been conducted to determine the effect of dietary carote-noids on gilthead seabream broodstock performance and their relation as antioxidants with dietary n-3 highly unsat-urated fatty acid (HUFA) levels. In addition, the high cost of synthetic sources of carotenoids is leading to the search for new natural carotenoid sources such as paprika oleo-resin. Four experimental diets containing two combined levels of carotenoids from paprika oleoresin (40 and 60 mg kg)1) and n-3 HUFA (25 and 40 g kg)1) were respectively fed to triplicate groups of gilthead seabream (Sparus aurata) broodfish. Elevation of n-3 HUFA dietary levels from 25 to 40 g kg)1 significantly improved gilthead seabream broodstock performance in terms of egg viability, hatching rates and fecundity. Besides, it markedly increased egg contents in HUFAs which play important energetic and structural roles and improve embryo development. Both arachidonic acid and eicosapentaenoic acid (20:5n-3) egg contents were more readily affected by dietary n-3 HUFA than docosahexaenoic acid. HUFA levels did not caused any negative effect suggesting an optimized content of antioxi-dants in broodstock diets. Increase in dietary carotenoids from 40 to 60 mg kg)1 increased carotenoid contents in eggs and significantly improved egg fertilization rates suggesting an important sperm cellÕs protective role by reducing the risk of lipid peroxidation which is detrimental for sperm motility. The increased inclusion of dietary paprika oleoresin enhanced egg carotenoid deposition and improved fish reproductive performance, denoting the high nutritional value of this product as a source of carotenoids for brood-stock of this species. KEY WORDS
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.
The main aim of the current study was to compare the accuracy of selection for muscle content of fat and the health-promoting omega-3 fatty acids EPA and DHA in Atlantic salmon, by varying the sources of genetic information used in the estimation of breeding values. The following genetic information sources were compared: pedigree, SNP-chip markers and allele-specific expression markers.
The results showed that differences between information sources were in general small, and different genetic information performed best for different traits. SNP-chip performed best for DHA, and pedigree performed best for EPA.
Knowledge from gene expression analysis of a few individuals can be utilized to select a small panel of markers that perform relatively well. Genetic markers of allele-specific expression were able to capture a lot of genetic variation for DHA, but did not give significantly higher accuracies when combined with SNP-chip or pedigree information.
The cross-validation accuracies for selection for DHA and EPA were moderate and offer possibilities for selection for these traits, especially if one extends the reference data set to a much bigger population, with more sibs per selection candidate.
Information on phenotypic and genetic (co)variance for production traits in
turbot is required to improve breeding programs. So far, information on
morphometric growth traits is sparse and completely lacking on quality
carcass traits like fillet weight or fillet yield for turbot. As part of a
long-term study we explored the phenotypic and genetic (co)variance of 16
biometrical and carcass traits of three different European turbot strains.
Fish were reared under commercial grow-out conditions, including size
grading. We used molecular relatedness (MR) methods based on genotyping with
96 microsatellite markers and animal models. We included an adapted condition
factor for Pleuronectiformes (FCIPLN) and average daily weight
gain (ADG) between the ages of 300 and 500 d post-hatch (dph) for their
potential correlation with body weight at harvest. Heritability estimates for
all traits were low to medium (0.04–0.29) when strains were jointly
analyzed. Separate analysis of strains yielded higher heritability estimates
(0.12–0.43). Genetic correlations between weight-related traits were highly
positive (0.70–0.99), while runs with yield and ratio traits often resulted
in unreliable estimates of genetic correlation due to high standard errors.
Body weight (h2=0.19), fillet yield (h2=0.15), and dressing
percentage (h2=0.17) are particularly promising selection traits for
turbot breeding.
Nutrition during periconception and early development can modulate metabolic routes to prepare the offspring for adverse conditions through a process known as nutritional programming. In gilthead sea bream, replacement of fish oil (FO) with linseed oil (LO) in broodstock diets improves growth in the 4-month-old offspring challenged with low-FO and low-fishmeal (FM) diets for 1 month. The present study further investigated the effects of broodstock feeding on the same offspring when they were 16 months old and were challenged for a second time with the low-FM and low-FO diet for 2 months. The results showed that replacement of parental moderate-FO feeding with LO, combined with juvenile feeding at 4 months old with low-FM and low-FO diets, significantly ( P <0·05) improved offspring growth and feed utilisation of low-FM/FO diets even when they were 16 months old: that is, when they were on the verge of their first reproductive season. Liver fatty acid composition was significantly affected by broodstock or reminder diets as well as by their interaction. Moreover, the reduction of long-chain PUFA and increase in α -linolenic acid and linoleic acid in broodstock diets lead to a significant down-regulation of hepatic lipoprotein lipase ( P <0·001) and elongation of very long-chain fatty acids protein 6 ( P <0·01). Besides, fatty acid desaturase 2 values were positively correlated to hepatic levels of 18 : 4 n -3, 18 : 3 n -6, 20 : 5 n -3, 22 : 6 n -3 and 22 : 5 n -6. Thus, this study demonstrated the long-term nutritional programming of gilthead sea bream through broodstock feeding, the effect of feeding a ‘reminder’ diet during juvenile stages to improve utilisation of low-FM/FO diets and fish growth as well as the regulation of gene expression along the fish’s life-cycle.
Nile Tilapia breeding programs have been focused on growth improvement by selecting for either body weight (BW) or daily weight gain (DWG). Along with growth traits, yield and quality traits are also of great importance in livestock breeding. Our objective was to evaluate the feasibility of including fillet yield and quality traits as selection criteria for improving performance in Nile tilapia. The fish used in this study came from a population of 3 generations undergoing selection (Aqua America Company, Brazil). Pedigree information was available for 5,263 fish. Phenotypes for body weight at 290 days (BW290) and daily weight gain (DWG) were measured on 2,585 males and females, fillet weight (FW) and fillet yield (FY) were measured on 1,198 males, and fillet fat content (FAT) was measured on 1,136 males. Variance components were estimated in single and two-trait models using GIBBS1f90, and the post-analyses were carried out using POSTGIBBSF90, both from the BLUPF90 family of programs. For all analyses, spawning was considered as a random common environmental effect; harvest weight, weight at tagging, and age were used as covariables for DWG and BW; body weight at slaughter was used as a covariable for FW, FY, and FAT; floating cage and sex were included as fixed effects for all traits and for BW290 and DWG, respectively. Heritability estimates for DWG, BW, and FW were close to 0.23, whereas FY had the highest heritability (0.32) and FAT had the lowest (0.20). Genetic correlations of DWG with FY and FAT were −0.09 and −0.4, respectively; BW290 with FY and FAT were −0.1 and −0.32, respectively. The only positive correlation was between FY and FAT (0.6). Negative correlations between growth and fillet traits indicate an increase in guts and carcass weight in bigger fish, which is not desirable. Based on the estimated heritabilities, the genetic improvement of fillet yield and quality traits can be effective and should be included in the selection criteria. These results are particularly important for FW and FY since there is a market interest on increasing fillet yield. In addition, fillet quality traits such as FAT are also of interest to enhance meat quality.
Docosahexaenoic acid (DHA) plays important physiological roles in vertebrates. Studies in rats and rainbow trout confirmed that DHA biosynthesis proceeds through the so-called “Sprecher pathway”, a biosynthetic process requiring a Δ6 desaturation of 24:5n−3 to 24:6n−3. Alternatively, some teleosts possess fatty acyl desaturases 2 (Fads2) that enable them to biosynthesis DHA through a more direct route termed the “Δ4 pathway”. In order to elucidate the prevalence of both pathways among teleosts, we investigated the Δ6 ability towards C24 substrates of Fads2 from fish with different evolutionary and ecological backgrounds. Subsequently, we retrieved public databases to identify Fads2 containing the YXXN domain responsible for the Δ4 desaturase function, and consequently enabling these species to operate the Δ4 pathway. We demonstrated that, with the exception of Δ4 desaturases, fish Fads2 have the ability to operate as Δ6 desaturases towards C24 PUFA enabling them to synthesise DHA through the Sprecher pathway. Nevertheless, the Δ4 pathway represents an alternative route in some teleosts and we identified the presence of putative Δ4 Fads2 in a further 11 species and confirmed the function as Δ4 desaturases of Fads2 from medaka and Nile tilapia. Our results demonstrated that two alternative pathways for DHA biosynthesis exist in teleosts.
Gilthead sea bream (Sparus aurata) is a species of paramount importance to the Mediterranean aquaculture industry, with an annual production exceeding 140,000 metric tons. Pasteurellosis due to the Gram-negative bacterium Photobacterium damselae subsp. piscicida (Phdp) causes significant mortality, especially during larval and juvenile stages, and poses a serious threat to bream production. Selective breeding for improved resistance to pasteurellosis is a promising avenue for disease control, and the use of genetic markers to predict breeding values can improve the accuracy of selection, and allow accurate calculation of estimated breeding values of nonchallenged animals. In the current study, a population of 825 sea bream juveniles, originating from a factorial cross between 67 broodfish (32 sires, 35 dams), were challenged by 30 min immersion with 1 × 10⁵ CFU virulent Phdp. Mortalities and survivors were recorded and sampled for genotyping by sequencing. The restriction-site associated DNA sequencing approach, 2b-RAD, was used to generate genome-wide single nucleotide polymorphism (SNP) genotypes for all samples. A high-density linkage map containing 12,085 SNPs grouped into 24 linkage groups (consistent with the karyotype) was constructed. The heritability of surviving days (censored data) was 0.22 (95% highest density interval: 0.11–0.36) and 0.28 (95% highest density interval: 0.17–0.4) using the pedigree and the genomic relationship matrix respectively. A genome-wide association study did not reveal individual SNPs significantly associated with resistance at a genome-wide significance level. Genomic prediction approaches were tested to investigate the potential of the SNPs obtained by 2b-RAD for estimating breeding values for resistance. The accuracy of the genomic prediction models (r = 0.38–0.46) outperformed the traditional BLUP approach based on pedigree records (r = 0.30). Overall results suggest that major quantitative trait loci affecting resistance to pasteurellosis were not present in this population, but highlight the effectiveness of 2b-RAD genotyping by sequencing for genomic selection in a mass spawning fish species.
The gilthead sea bream (Sparus aurata L.) is one of the most important marine fish species produced in southern European countries. Over the last two decades, microsatellites have become a powerful tool for DNA studies of fish populations, making it possible to establish existing genealogical relationships between individuals and to perform reliable estimates of genetic parameters. In the present study, a total of 7959 fish (494 breeders and 7465 fry) were genotyped using two rounds of multiplex reactions with four microsatellite markers each. Offspring were assigned based on the Mendelian exclusion principles, using FAP program. Genealogical information was successfully obtained for more than 83 % of the progeny. Heritability estimates were close to 0.40 in all cases and for all considered traits. The lowest value was for the length at first age (350 ± 6 dph) and the highest for the length at the second age (500 ± 7 dph). The heritabilities for the first and the second weight were similar although somewhat higher for the second age, but not significant. The highest genetic correlations were found between weight and length at the same age and the lowest between weight and length at different ages. Based on the results of this study, it seems reasonable to expect that the implementation of a breeding program for improved growth in this population of gilthead sea bream will offer comparable performances to those achieved in other populations and species of great success in aquaculture around the world.
The use of selective breeding is still relatively limited in aquaculture species. Information on such activities is sparse, hindering an overall evaluation of their success. Here, we report on the results of an online survey of the major aquaculture breeding companies operating in Europe. Six main reared fish species were targeted. A total of 31 respondents contributed to the survey, representing 75 % of European breeding organizations. Family-based breeding schemes were predominant, but individual selection was more frequently applied in marine species. Artificial fertilization is the preferred means of reproduction; however, mass spawning is often used as a fallback method. The most frequently selected trait is growth performance, but the number of selected traits has been increasing over the years through the addition of traits such as disease resistance or product quality. The use of molecular tools is now common in all programs, mainly for pedigree traceability. An increasing number of programs use either genomic or marker-assisted selection. Results related to the seed production market confirmed that for Atlantic salmon there are a few dominant players at the European level, with 30–50 % market share. Only part of the European fish aquaculture industry today fully exploits selective breeding to the best advantage. A larger impact assessment still needs to be made by the remainder, particularly on the market share of fish seed (eggs, larvae or juveniles) and its consequences for hatchery stability.
Morphological abnormalities in farmed gilthead seabream (Sparus aurata) are a major problem as it entails significant economic losses. In this study, 3 large scale experiments under different conditions of spawning, offspring handling and breeders phenotype were performed to analyze the inheritance of 4 types of deformities in this species: lack of operculum, lordosis, vertebral fusion, which are 3 of the most important skeletal deformities, and LSK, which is a consecutive repetition of lordosis/scoliosis/kyphosis. In Exp. [1] (mass spawning and fingerling sorting), 900 fish were analyzed at 509 d post-hatching: 846 fish that had been on-grown in a farm and 54 LSK-deformed fish that had been reared separately after being selected during the fingerling sorting process. A total of 89 families were represented. A statistically significant association between 5 of these families (from 6 breeders) and LSK-deformed fish was found. In Exp. [2] (mass spawning and no fingerling sorting), 810 fish were analyzed at 2 ages: 179 and 689 d post-hatching. Significant relationships between 2 of the breeders and 2 of the families with the lack of operculum prevalence of their descendants were found at 689 d but not at 179 d. Heritabilities: 0.09 ± 0.09 at 179 d and 0.17 ± 0.08 at 689 d. Column deformities prevalence was low and no association with family was observed. Family relationships were determined by microsatellites multiplex PCR in both experiments. In Exp. [3] (designed mating), sires suffering from lordosis or lack of operculum or vertebral fusion deformities were mated with non-deformed dams and a mass-spawning mating was considered as a control. After analyzing 11,503 offspring at 159 d post-hatching, a significant relationship between each deformity prevalence and the mating of breeders suffering from the same deformity was observed. In addition, a significant prevalence of lack of operculum in offspring from lordotic matings was observed. Heritabilities ranged from 0.34 to 0.46 for the 3 deformities. The results of the present study suggest that these deformities have a genetic origin. They also suggest that the sorting process is not recommended and that producers should consider these deformities in genetic breeding programs to significantly improve their fish morphological quality and to minimize farmed fish deformities incidence.
In Eurasian perch (Perca fluviatilis), the variability in spawning quality is a major limiting factor for successful production, especially when breeders are fed with an artificial diet. The influence of the dietary DHA/EPA/AA ratio on the egg and larval quality and on the fatty acid and lipid class composition of eggs has been investigated in perch broodstock. Two experimental diets (16% lipids) with two different DHA/EPA/AA ratios, D1 (3/2/2) and D2 (23/9/1), were compared with a natural diet consisting of cultured carp juveniles, CC (10/10/1) and with a commercial diet for salmonids, CDS (14/16/1). Percentages of fertilization and hatching were comparable between fish fed D1, D2 and CC, with the highest hatching rate observed for D1 (63.5 ± 3.8%). These diets supported better values than the CDS. Larval survival and TL50 observed after osmotic stress were higher for the D1 group, followed by larvae produced by fish fed D2 and CC. Larvae from fish fed D1, D2 and CC were significantly more robust than larvae from the CDS group. Differences were observed regarding the fatty acid (FA) profile in the eggs, which was related to the dietary FA composition. The results indicate that a ratio of 3/2/2 seemed to be effective for obtaining eggs and larvae of good quality.
Gilthead seabream (Sparus aurata) is one of the most important species among intensively reared fish in the Mediterranean region. Although there is a considerable interest in the genetic improvement of this species, many of the genetic parameters of commercial stocks have yet to be investigated. The effective population size (Ne) of a commercial gilthead seabream broodstock was determined using microsatellite analysis. Eight microsatellite loci were used to ensure a high confidence to the parental assignment of offspring from several mass-spawning events. The Ne was consistently low, ranging from 14 to 18, between photoperiod-controlled broodstock groups. This equated to an inbreeding rate of 2.7–3.5% per generation. The primary constraint on Ne was the high variance in family size and fewer males than females contributing to each spawning. The contribution of male parents to spawning was also more variable than females. Log-linear modelling of offspring counts revealed a significant quadratic relationship, with intermediate parental weights being optimum. The relationship between parental weight and contribution may be evidence of an optimum age structure to the broodstock, or stabilising selection. Low Ne in commercial stocks of gilthead seabream could lead to an increased risk of inbreeding through the practice of broodstock replacement from within same-farm populations.
It is of great importance to increase the natural disease resistance of farmed fish. Response to direct selection for increased survival in commercial environments has been low, basically due to inaccurate records of the trait. However, challenge tests with family groups which were infected with specific pathogens showed significant genetic variation in mortality, indicating that improvement by selection is possible. Several studies have shown a significant positive genetic correlation between growth rate and survival. Therefore survival would be expected to increase as a correlated response when selecting for growth rate. Significant genetic variation has been found in immunological parameters, but more knowledge is needed about the genetic correlations between these parameters and survival before indirect selection for increased survival can be applied. Heterosis for survival has not shown large effects. However, it may be still of interest to develop resistant lines to specific diseases and cross them to produce hybrids. Disease resistance genes have not been identified in fish. However, the production of transgenic fish with enhanced resistance to specific diseases remains as a possibility for the future.
This paper discusses the restricted maximum likelihood (REML) approach for the estimation of covariance matrices in linear stochastic models, as implemented in the current version of the VCE package for covariance component estimation in large animal breeding models. The main features are: 1) the representation of the equations in an augmented form that simplifies the implementation; 2) the parametrization of the covariance matrices by means of their Cholesky factors, thus automatically ensuring their positive definiteness; 3) explicit formulas for the gradients of the REML function for the case of large and sparse model equations with a large number of unknown covariance components and possibly incomplete data, using the sparse inverse to obtain the gradients cheaply; 4) use of model equations that make separate formation of the inverse of the numerator relationship matrix unnecessary. Many large scale breeding problems were solved with the new implementation, among them an example with more than 250 000 normal equations and 55 covariance components, taking 41 h CPU time on a Hewlett Packard 755.
This study establishes that ovulated female goldfish release F type prostaglandins (PGFs) to the water where they stimulate male spawning behavior and comprise the goldfish postovulatory pheromone. We first demonstrated that ovulated and prostaglandin-injected female goldfish release immunoreactive PGFs to the water. Next, using electro-olfactogram recording (EOG), we determined that waterborne prostaglandins function as potent olfactory stimulants for mature male goldfish. Prostaglandin F2 alpha (PGF2 alpha) and its metabolite 15-keto-prostaglandin F2 alpha (15K-PGF2 alpha) were the most potent prostaglandins; the former had a detection threshold of 10(-10) M and the latter a detection threshold of 10(-12) M. Studies of prostaglandin-injected fish indicated that PGF metabolites are an important component of the pheromone. Cross-adaptation experiments using the EOG demonstrated that goldfish have separate olfactory receptor sites for PGF2 alpha and 15K-PGF2 alpha that are independent from those that detect other olfactory stimulants. Finally, we established that male goldfish exposed to low concentrations of waterborne PGFs exhibit reproductive behaviors similar to those elicited by exposure to the odor of ovulated fish. Together with our recent discovery that a steroidal maturational hormone functions as a preovulatory "priming" pheromone for goldfish, these findings suggest that hormones and their metabolites may commonly serve as reproductive pheromones in fish.
The interaction between essential dietary components and changes in tissue nutrient reserves, egg quality and egg composition, were studied from 60 d before and during the spawning of Sparus aurata broodstock. Fish were given isonitrogenous (550 g/kg dry weight) and isolipidic (100 g/kg dry weight) diets, based on protein and lipid extracts of squid meal. Diets differed in the levels of n-6 (10-30 mg/g dry weight) and n-3 (0-10 mg/g dry weight) essential fatty acids. The effects of these diets on biochemical and fatty acid composition of body tissues, and the subsequent effects on egg composition and egg viability were measured. Dietary essential fatty acids were mostly incorporated into the liver, ovaries, digestive tract and associated adipose tissues. The lipid composition of these tissues reached an equilibrium with dietary lipid composition within 15 d of feeding on any given diet. Muscle and gill cartilage tissues did not show any significant changes in their biochemical and fatty acid composition, even after 60 d feeding. Egg viability decreased significantly within 10 d of feeding the broodstock with a diet deficient in n-3 highly unsaturated fatty acids (n-3 HUFA). The levels of n-3 HUFA in both polar and neutral fractions of egg lipid were directly correlated with their levels in the broodstock diet. When the total amount of egg n-3 HUFA dropped below 17 mg/g dry weight, egg viability and larvae hatching rate decreased by 53% and 47% respectively. These results suggest that the biochemical composition of organs involved in S. aurata reproduction are highly sensitive to the nutritional value of the diet, which affects egg and larval quality rapidly.
Environmental factors such as nutritional interventions during early developmental stages affect and establish long-term metabolic changes in all animals. Diets used during the spawning period causes a nutritional programming effect in offspring of gilthead sea bream and affects long-term metabolism. Studies showed modulation of genes such as fads2 which is considered to be a rate-limiting step in the synthesis of n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA). However, it is still unknown whether this adaptation is related to the presence of precursors or limitations in the pre-formed products, n-3 LC-PUFA, contained in the diets used during nutritional programming. This study investigates the combined effects of nutritional programming through broodstock diets during the spawning period and broodfish showing higher or lower fads2 expression levels in the blood after 1-month feeding with a diet containing high levels of plant protein sources and vegetable oils (VM/VO). Broodfish showing high fads2 expression had a noticeable improvement in the spawning quality parameters as well as on the growth of 6 months old offspring when challenged with a high VM/VO diet. Further, nutritional conditioning with 18:3n-3 rich diets had an adverse effect in comparison to progeny obtained from fish fed high fish meal and fish oil (FM/FO) diets, with a reduction in growth of juveniles. Improved growth of progeny from the high fads2 broodstock combined with similar muscle fatty acid profiles is an excellent option also for tailoring and increasing the flesh n-3 LC-PUFA levels to meet the recommended dietary allowances for human consumption.
Nutritional intervention with vegetable oils (VO) supplemented to fish broodstock diets enhances progeny ability to utilize low fish meal (FM) and fish oil (FO) diets. However, the intervention with vegetable meals (VM) in broodstock diets has been scarcely tested in marine fish. This study aims to determine the effect of FM replacement by VM alone or in combination with FO replacement by VO as a programming tool. Different broodstocks of gilthead sea bream were fed one of three diets: one contained 35% FM and 10% FO, another contained VM in replacement of FM (FM: 15%) or a third one had both VM and VO in replacement of FM and FO (15% FM and 2.7% FO). At the weight of 3 g, their offspring were challenged with a low FM (5%) and FO (3%) diet for 45 days. FM replacement by VM in broodstock diets did not affect fish reproductive performance but in offspring juveniles reduced growth and feed efficiency and in liver, altered fatty acids profiles and down-regulated fatty acyl desaturase 2 (fads2) expression. Combined supplementation of VM and VO in broodstock diets led to a poor reproductive performance, reducing female fecundity and the egg content in eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA). At molecular level, the expression of fads2 and target of rapamycine (tor) genes in the eggs were upregulated. Similarly, in liver of juvenile progenies fads2 and elongase of very long chain fatty acids 6 (elovl6) expression were up-regulated, whereas fads2 expression was correlated to sterol regulatory element-binding protein transcription factor 1 (srebp1). However, methylation rates of CpG rich regions in fads2 promoter were not significantly different among juvenile groups. Thus, the replacement of FM by VM, alone or in combination with FO in diets for gilthead sea bream broodstock negatively affected growth performance of juvenile offspring, whereas the replacement of FO by VO enhanced the fatty acid desaturase and elongase activities in the offspring, especially when juveniles were fed a diet with a high replacement of FM and FO by VM and VO.
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.
Lordosis, lack of operculum and failure to inflate the swimbladder constitute a major problem for the gilthead sea bream aquaculture industry. In this study, the effect of the origin of the broodstock on these major anomalies in juvenile sea bream was analyzed. A population of farmed sea bream (n = 909) obtained by industrial mass-spawning from broodstock from three different origins [Cantabrian Sea (CAN), the Atlantic Ocean (ATL) and Mediterranean Sea (MED)] and reared under communal conditions was analyzed from X-ray photograph for skeletal deformities and for uninflated swimbladder. Lordosis and lack of operculum were the most common deformities observed in this study. Juveniles from CAN showed the lowest frequency of skeletal deformities as well as the lowest frequency of uninflated swimbladder. Differences among origins could be partly explained through their different genetic background, but also environmental conditions in the initial facilities and genotype x environment interaction should be considered. A posteriori reconstruction of pedigree was carried out using a microsatellite multiplex (SMsa1) to estimate genetic parameters (heritabilities and genetic correlations) for these traits. Considerable heritabilities were estimated for lordosis [0.53 (0.25–0.77)], lack of operculum [0.37 (0.01–0.81)] and uninflated swimbladder [0.36 (0.12–0.72)] with a positive genetic correlation between uninflated swimbladder and lordosis [0.48 (0.07–0.97)], first reported in this species. All these findings should be relevant for the establishment of successful breeding programs in the aquaculture of this species.
Different mating techniques were evaluated for success rates of producing genetically related groups of gilthead seabream, Sparus aurata. Overall, success rates were low; only 10% of attempted artificial stripping yielded offspring, single pair "natural" spawning was successful in 22% of the attempts, and progeny testing (15 females with one male) was successful in 44% of the attempts. While relatively few families were produced, analysis of their growth suggested substantial genetic differences among them. However, it seems likely that an extensive family selection program would require, in view of reproductive constraints, maintenance of a prohibitively large number of S. aurata broodstock. Alternatives such as mass selection may offer a more practical option for genetic improvement.
Despite extensive mariculture of the gilthead seabream, Sparus aurata, in the Mediterranean basin, there are no heritability estimates for growth in this or any other cultured warm water marine teleost, and so it is unknown whether selection for faster growing fish would result in genetic improvement. In the present study, we estimated heritability for weight in the Eilat hatchery strain of S. aurata, using single-generation mass selection procedures. Down, control, up and extreme up ("jumper") selected male groups were crossed with randomly chosen unselected females. Progeny groups were cultured in replicates under communal and separate rearing conditions. Heritability estimates for weight varied, but overall were positive and of a moderate magnitude.
Growth rates and the presence of deformities can be affected by the use of different rearing systems aswell as by
the different genetic origins of the stocks. At the same time, strategies that involve the development of selection
schemes for these traits of economic interest are scarce. In this study the effect of the origin of the broodstock on
growth traits and external deformities as well as genetic parameters (heritabilities and genetic correlations) for
these traits were estimated at different ages (days post-hatching; dph). For this purpose, a population of farmed
gilthead sea breamwas obtained fromthree broodstock of different origins along the Spanish coasts [Cantabrian
Sea (CAN), the Atlantic Ocean (ATL) and Mediterranean Sea (MED)] and reared under the same intensive conditions.
Parental assignments between breeders and their offspring were carried out a posteriori using a microsatellite
multiplex (SMsa1). Juveniles from MED showed the fastest growth while those from ATL showed the
slowest growth and the highest incidence of vertebral column deformities. Differences among origins could be
explained not only through their different genetic backgrounds but also by environmental conditions in the initial
facilities, where different origins were reared separately, and by genotype × environment interactions.
Growth traits showed low heritabilities at 163 dph (0.11 ± 0.03) and medium at 690 dph (0.25 ± 0.06 for
weight; 0.22± 0.07 for length) suggesting that selection at the later age would be more appropriate. Both traits
were highly and positively correlated at both ages at the genetic and phenotypic levels. External deformities in
the vertebral column as well as in the operculum showed medium–high heritability at both studied ages with
higher values at 690 dph (0.56 [0.17–0.69] and 0.46 [0.20–0.90], respectively). These results revealed that the ontogenesis
of deformities exhibits a partial genetic basis. Nevertheless, for those in the rest of the head the heritability
was close to zero. Initially, positive genetic correlations between growth and deformities in the vertebral
column were observed (83% probability of being positive for weight-vertebral column deformity; 81% for
length-vertebral column deformity). However, these correlations seem to be negative at 690 dph (94.2% probability
of being negative for weight-vertebral column; 80.6% for length-vertebral column). Results confirm that it
could be recommended to eliminate deformed fish froma breeding nucleus and later, select on growth. All these
findings should be relevant for the establishment of successful breeding programs in the aquaculture of this
species.
In the 40 years since the essentiality of polyunsaturated fatty acids (PUFA) in fish was first established by determining quantitative requirements for 18:3n − 3 and 18:2n − 6 in rainbow trout, essential fatty acid (EFA) research has gone through distinct phases. For 20 years the focus was primarily on determining qualitative and quantitative EFA requirements of fish species. Nutritional and biochemical studies showed major differences between fish species based on whether C18 PUFA or long-chain (LC)-PUFA were required to satisfy requirements. In contrast, in the last 20 years, research emphasis shifted to determining “optimal” levels of EFA to support growth of fish fed diets with increased lipid content and where growth expectations were much higher. This required greater knowledge of the roles and functions of EFA in metabolism and physiology, and how these impacted on fish health and disease. Requirement studies were more focused on early life stages, in particular larval marine fish, defining not only levels, but also balances between different EFAs. Finally, a major driver in the last 10–15 years has been the unavoidable replacement of fish oil and fishmeal in feeds and the impacts that this can have on n − 3 LC-PUFA contents of diets and farmed fish, and the human consumer. Thus, dietary n − 3 in fish feeds can be defined by three levels. Firstly, the minimum level required to satisfy EFA requirements and thus prevent nutritional pathologies. This level is relatively small and easy to supply even with today's current high demand for fish oil. The second level is that required to sustain maximum growth and optimum health in fish being fed modern high-energy diets. The balance between different PUFA and LC-PUFA is important and defining them is more challenging, and so ideal levels and balances are still not well understood, particularly in relation to fish health. The third level is currently driving much research; how can we supply sufficient n − 3 LC-PUFA to maintain these nutrients in farmed fish at similar or higher levels than in wild fish? This level far exceeds the biological requirements of the fish itself and to satisfy it we require entirely new sources of n − 3 LC-PUFA. We cannot rely on the finite and limited marine resources that we can sustainably harvest or efficiently recycle. We need to produce n − 3 LC-PUFA de novo and all possible options should be considered.
The complete removal of fishmeal (FM) and fish oil (FO) is required to promote the sustainable development of aquaculture and for that, fast growing high quality fish that are fed without FM and FO are necessary. Early nutritional programming may allow the production of fish better adapted to utilize diets with vegetable meals (VM) and oils (VO). The main objective of this study was to research in the potential value of fatty acids as modulators of early nutritional programming in marine fish for a better utilisation of VO/VM. For that purpose gilthead sea bream (Sparus aurata) broodstock were fed four different replacement levels of FO by linseed oil (LO) and their effect on fecundity and spawn quality, egg composition, Δ-6-desaturase (Δ6D) gene expression, progeny growth performance and their growth response to a challenge with diets low in FO and FM, but high in VO and VM. The results showed that feeding gilthead sea bream broodstock with high LO diets had very long-term effects on the progeny. Thus, FO replacement by LO up to 80-100% in broodstock diets for gilthead sea bream not only reduced fecundity and spawn quality, but also growth of 45 dah and 4-month-old juveniles, as well as Δ6D gene expression. However, when the 4 month-old juveniles were fed with a low FM and FO diet, even those from broodstock fed only 60% replacement of FO by LO showed a higher growth and feed utilization than juveniles from parents fed FO. These results demonstrate the interesting potential of early nutritional programming of marine fish by broodstock feeding to improve long-term performance of the progeny. Further studies are being conducted to determine optimum nutrient levels in the broodstock diets and the molecular mechanisms implied to develop effective nutritional intervention strategies for this species.
One of the most important problems of fish aquaculture is the high incidence of fish deformities, which are mainly skeletal. In this study, genetic parameters on gilthead seabream (Sparus aurata L.) for skeleton deformities at different ages (179, 269, 389, 539 and 689 days) and their correlations with growth traits were estimated, as were as their genotype × environment interactions (G × E) at harvesting age. A total of 4093 offspring from the mass spawning of three industrial broodstocks belonging to the PROGENSA(®) breeding programme were mixed and on-grown by different production systems in four Spanish regions: Canary Islands (tanks and cage), Andalusia (estuary), Catalonia (cage) and Murcia (cage). Parental assignment was inferred using the standardized SMsa1 microsatellite multiplex PCR. From three broodstocks, 139 breeders contributed to the spawn and a total of 297 full-sibling families (52 paternal and 53 maternal half-sibling families) were represented. Heritabilities at different ages were medium for growth traits (0.16-0.48) and vertebral deformities (0.16-0.41), and low for any type of deformity (0.07-0.26), head deformities (0.00-0.05) and lack of operculum (0.06-0.11). The genetic correlations between growth and deformity traits were medium and positive, suggesting that to avoid increasing deformities they should be taken into account in breeding programmes when growth is selected. The G × E interactions among the different facilities were weak for length and deformity and strong for growth rate during this period. These results highlight the potential for the gilthead seabream industry to reduce the prevalence of deformities by genetic improvement tools.
© 2015 Stichting International Foundation for Animal Genetics.
Dietary omega-3 long chain polyunsaturated fatty acids (n-3 LCPUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have a marked effect on fish behavior. There is limited information on the mechanisms involved in this effect and its relation to neuron development and functioning. Deficiency of n-3 LCPUFA reduces fish escape swimming. Mauthner cells (M-cell) are neurons responsible for initiating an escape response. The aim was to compare the effect of dietary DHA and EPA on escape behavior and neuronal activity of sea bream larvae. We studied burst swimming speed as a measure of behavior. M-cell activity was studied by ChAT immuno-fluorescence. Feeding the lowest n-3 LCPUFA levels a lower burst swimming speed. Increase in dietary EPA did not significantly improve escape response. Elevation of dietary DHA was correlated with a higher burst speed denoting the importance of this nutrient for escape swimming. Incorporation of DHA into larval tissues was proportional to DHA dietary levels and significantly correlated with burst speed. In addition, a higher immunoreactivity to ChAT, associated to a higher neural activity, was found in M-cell of larvae fed higher dietary DHA contents. These results show first evidence of n-3 LCPUFA on fish neuronal activity and their implications in behavior, denoting that DHA boosts escape swimming and this effect is at least partly mediated by the increase in neural activity of M-cell.
It has been exciting to follow the rapid development of aquaculture production in Norway, and internationally, since 1971. As an animal breeder I am particularly impressed with the genetic gain obtained for growth rate, and also for disease resistance in several aquatic species, which is five to six times higher than what has been achieved in terrestrial farm animals. This is illustrated in five selected projects I have been involved in. The sad story is, however, that only less than 10% of the world's aquaculture production is based on genetically improved stocks. The big challenge for the future is to develop more selective breeding programs for existing and new emerging aquaculture species in order to increase the production of this nutritious food source and to improve the efficiency of the use of feed, water, land and labor resources.
Lipid and fatty acid composition of broodstock diet have been identified as major dietary factors that determine successful reproduction and survival of offspring. Some fish species readily incorporate dietary unsaturated fatty acids into eggs, even during the course of the spawning season. Highly unsaturated fatty acids (HUFA) with 20 or more carbon atoms affect, directly or through their metabolites, fish maturation and steroidogenesis. In some species, HUFA in broodstock diets increases fecundity, fertilization and egg quality. As in higher vertebrates, vitamin E deficiency affects reproductive performance, causing immature gonads and lower hatching rate and survival of offspring. For example, elevation of dietary α-tocopherol levels has been found to reduce the percentage of abnormal eggs and increase fecundity in the gilthead seabream (Sparus aurata). Ascorbic acid has also been shown to play an important role in salmonid reproduction, where the dietary requirement of broodstock was higher than that of juveniles. Among different feed ingredients, cuttlefish, squid and krill meals are recognized as valuable components of broodstock diets. The protein component of cuttlefish and squid together with their optimal concentration of HUFA appear to be responsible for their positive effect on reproductive performance. Both polar and nonpolar lipid fractions of raw krill were found to effectively improve egg quality. © 2001 Published by Elsevier Science B.V.
A variety of morphological, biological and biochemical parameters of freshly spawned eggs of gilthead seabream (Sparus aurata L.) were studied to determine the optimum n − 3 HUFA level in broodstock diets necessary to obtain a high-quality spawn. The effect of very high dietary n − 3 HUFA levels on fish reproduction was also investigated. Broodstock were separated into 8 groups and fed four diets containing different levels of n − 3 HUFA, ranging from 1.13 to 3.15%, for 3 months. Spawning and egg qualities were evaluated daily by 7 parameters. Besides, 8 samples of eggs were taken during the experimental period and were analyzed for proximate and fatty acid composition. After 3 weeks of feeding, significantly improved spawning quality in the broodstock fed 1.6% n − 3 HUFA was observed in terms of fecundity, hatching and larval survival. Unfertilized egg rates were significantly reduced by the increase in dietary 20:5n − 3. The highest level of dietary n − 3 HUFA was associated with a decreased fecundity and yolk sac hypertrophy in just hatched out larvae, n − 3 HUFA content in the eggs showed a positive correlation with dietary n − 3 HUFA, mainly due to the change in 20:5n − 3 content of the eggs.
The mode of action of highly unsaturated fatty acids (HUFA) in regulating gilthead sea bream (Sparus aurata) head kidney (HK) cortisol production was studied through in vitro trials using a dynamic superfusion system. Fish were previously fed with different diets containing several inclusion levels of linseed oil (LO) or soyabean oil (SO) for 26 weeks. Five diets were tested; anchovy oil was the only lipid source for the control diet (fish oil, FO) and two different substitution levels (70 and 100 %) were tested using either LO or SO (70LO, 70SO, 100LO and 100SO). Fatty acid compositions of the HK reflected the dietary input, thus EPA, DHA, arachidonic acid and n-3 HUFA were significantly (P,0·05) reduced in fish fed vegetable oils compared with fish fed the FO diet. Feeding 70 or 100 % LO increased significantly (P,0·05) cortisol release in HK after stimulation with adrenocorticotrophic hormone (ACTH), while feeding SO had no effect on this response. Cortisol stimulation factor (SF) was increased in fish fed the 70LO and 100LO diets compared with fish fed the control diet. Moreover, eicosanoid inhibition by incubating the HK tissue with indomethacin (INDO) as a cyclo-oxygenase (COX) inhibitor, or nordi-hydroguaiaretic acid (NDGA) as a lipoxygenase (LOX) inhibitor, significantly reduced (P,0·05) the cortisol release after ACTH stimulation in the 70LO and 100LO diets. Cortisol SF was reduced in the FO, 70LO and 100LO diets when incubating the HK with INDO or NDGA, while it was increased in the 70SO diet. The present results indicate that changing the fatty acid profile of gilthead sea bream HK by including LO and/or SO in the fish diet affected the in vitro cortisol release, and this effect is partly mediated by COX and/or LOX metabolites.
Molecular tools to assist breeding programs in the gilthead sea bream (Sparus aurata L.) are scarce. A new multiplex PCR technique (OVIDORPLEX), which amplifies nine known microsatellite markers, was developed in this work. This multiplex system showed a high mean heterozygosity (> 0.800) and a high mean number of alleles per marker (> 14) when tested in two sea bream broodstocks (A: 40 breeders and B: 38 breeders). We tested this multiplex PCR for inferring parentage in a Spanish hatchery that graded the animals by size as part of their management procedure. The progeny of the broodstock were divided into fast- and slow-growth groups. Parentage studies revealed that this management procedure entailed a global reduction of the breeders' representation in progeny and that breeders' contributions were significantly unequal. Due to this, effective sample sizes fell to Nê ≈ 13–14 for fast- and Nê ≈ 18–24 for slow-growth progeny groups. These results imply a 3 to 4% rate of inbreeding per generation in the fast-growth group, which is more important to hatchery managers than the slow group. Not all the progeny were evaluated in this experiment (due to the discarding steps), and thus it is difficult to know if the phenotypic performance showed by the fast-growing progeny will be heritable. However, there were genetic differences between the differentiated growth progeny groups (fast vs. slow, FST values = 0.016 to 0.023; P < 0.01). We also identified breeders with significantly different contributions to the fast- (10 breeders) or to the slow- (15 breeders) growth progeny groups. Our results demonstrated that this new multiplex PCR could be useful for quantitative programs (breeding programs, detection of QTL, inbreeding control or reconstruction of fish genealogies) to improve the aquaculture of the gilthead sea bream (S. aurata).
This study tested the effect of the level of dietary phosphatidylcholine (PC) and its constituent medium-chain fatty acids on microdiet ingestion (μg diet larva−1 h−1) and the absorption rate of the free fatty acid [14C]16:0 (pmole larva−1 h−1) in 15, 20, 21, 25, 26, 30 and 31-day-old gilthead sea bream, Sparus auratus L., larvae. Fish were fed four microdiets (A, B, C and D): microdiet A contained no phospholipid (PL), while microdiet B included 10 g kg−1Artemia nauplii PL (3.7 g kg−1 PC). Microdiets C and D contained 10 g kg−1 purified saturated PC dimyristoyl (C14:0) and polyunsaturated PC dilinoleoyl (C18:2[cis]−9,12), respectively.
Larvae from one or both of the PC microdiets demonstrated significantly higher (P < 0.05) ingestion rates (μg diet larva−1 h−1) than the non-PL microdiet control in 15, 21, 22, 25 and 26-day-old larvae and the Artemia PL microdiet in 15, 22 and 26-day-old larvae. However, microdiet ingestion and fatty acid absorption rate appeared to be independent of the associated medium carbon chain saturated or polyunsaturated fatty acid moiety of the PC diets. Apparent absorption, as measured by the retention of radio-labelled [14C]16:0 following 8 h of non-labelled microdiet feeding, was possibly related to feeding.
Commercial feeds for gilthead seabream are highly energetic, containing fish oil as the main lipid source. The steady production and raising prices of fish oil encourage the inclusion of vegetable oils in fish feeds. Fish oil could be at least partially substituted by vegetable oils in diets for marine species, being this substitution resulted in good feed utilization and maintenance of fish health, since imbalances in dietary fatty acids may alter the immunological status and stress resistance in fish.
Unsaturated long chain fatty acids modulate hormone secretion from a variety of endocrine glands, including the adrenal cortex. Oleic acid and linoleic acid have been shown to stimulate production of glucocorticoids in the absence of adrenocorticotropic hormone, but at a high concentration appeared to inhibit the action of this hormone. In the present study, the concentration dependence of the inhibitory actions of these two fatty acids was tested in collagenase-dispersed rat adrenal fasciculata cells, and the effects of both lipids on cAMP production were also determined. Adrenocorticotropic hormone stimulated steroid production from isolated cells approximately ten-fold above unstimulated cells. Oleic and linoleic acid significantly inhibited the response to this hormone by 44% and 54%, respectively. The half-maximally effective inhibitory concentration of both lipids was between 75-100 microM. A maximal concentration of adrenocorticotropic hormone increased cAMP secretion 138-fold above unstimulated cells. Oleic and linoleic acids inhibited the increase in cAMP secretion by 47% and 33%, respectively. It is concluded that pathophysiological concentrations of unsaturated fatty acids inhibit the action of adrenocorticotropic hormone on the adrenal gland, and that the mechanism of action of the lipids may be partly via inhibition of cAMP production.
Phospholipase A2 (PLA2; phosphatide 2-acylhydrolase, EC 3.1.1.4) activity from human platelets increases significantly when the enzyme is separated from an endogenous inhibitor(s). The inhibitor, associated mainly with a particulate fraction, has now been identified as a mixture of unsaturated fatty acids. Treatment of the inhibitor with trypsin, RNase, DNase, or heat did not diminish its inhibitory activity, which was extractable by organic solvents. Incubation of PLA2 with phospholipids or various neutral lipids, including saturated fatty acids, had little or no effect on enzymatic activity. In contrast, unsaturated fatty acids such as palmitoleic acid (16:1), oleic acid (18:1), linoleic acid (18:2), linolenic acid (18:3), arachidonic acid (20:4), all of which were detected in the particulate fraction, or longer chained unsaturated fatty acids inhibited PLA2 activity by 50% at approximately equal to 5 X 10(-7) M. The level of unsaturated fatty acids in the inhibitor fraction was equivalent to approximately equal to 10(-4) M, apparently sufficient to effectively inhibit PLA2 activity. Methylation of unsaturated fatty acids caused a complete loss of inhibitory activity, and subsequent demethylation restored the activity, suggesting that a free carboxyl group was necessary. Inhibition of PLA2 by unsaturated fatty acids appeared to be noncompetitive. PLA2 absolutely required Ca2+ for activity; the inhibition by unsaturated fatty acids was not reversed by Ca2+. The finding that unsaturated fatty acids are potent inhibitors of PLA2 would explain its generally low activity in human platelet extracts and its marked increase of activity during the course of enzyme purification.
A mixture of linoleic and alpha-linolenic acids (free non-esterified unsaturated fatty acids) administered for 3 weeks prior to injection of cortisol (10 mg/kg), or prior to immersion of rats in a 10 degree C saline bath, prevented elevation of blood levels of cortisol and cholesterol and deficits in Morris water maze spatial learning that usually accompany such stressful conditions. Differences from controls on all behavioural and biochemical measures were statistically significant (P < .05). It is proposed that induction of intense stress, and the associated increase in cortisol, cholesterol and other corticosteroids may damage hippocampal structures and help account for the cognitive decline witnessed in Alzheimer's disease and other age-related conditions. The modulation of these consequences by the fatty acid mixture may provide an alternative strategy for the study of stress markers and for the development of other intervention options in humans.