Early nutritional intervention can improve utilisation of vegetable-based diets in diploid and triploid Atlantic salmon (Salmo salar L.)

Optimizing reproductive performance in pangasius catfish broodstock: A review of dietary and molecular strategies

Pangasius catfish, a significant player in the global whitefish market, encounters challenges in aquaculture production sustainability. Quality broodstock maintenance and seed production are impeded by growth, maturation, and fecundity issues. This review investigates the efficacy of strategic nutrient composition and molecular strategies in enhancing broodstock conditions and reproductive performance across various fish species. A notable knowledge gap for Pangasius catfish hampers aquaculture progress. The review assesses nutrient manipulation's impact on reproductive physiology, emphasizing pangasius broodstock. A systematic review analysis following PRISMA guidelines was conducted to identify research trends and hotspots quantitatively, revealing a focus on P. bocourti and fertilization techniques. Addressing this gap, the review offers insights into dietary nutrients manipulation and genetic tool utilization for improved seed production, contributing to pangasius catfish aquaculture sustainability.

Modulation of metabolic and immunoregulatory pathways in the gut transcriptome of Atlantic salmon (Salmo salar L.) after early nutritional programming during first feeding with plant-based diet

Introduction

Plant-based nutritional programming is the concept of exposing fish at very early life stages to a plant-based diet for a short duration to improve physiological responses when exposed to a similar plant-rich diet at a later developmental stage. The mechanisms of action underlying nutritional programming have not been fully deciphered, and the responses may be controlled at multiple levels.

Methods

This 22-week study examines gut transcriptional changes after nutritional programming. Triplicate groups of Atlantic salmon were fed with a plant (V) vs. a marine-rich (M, control) diet for 2 weeks (stimulus phase) at the first exogenous feeding. Both stimulus fish groups (M and V fish) were then fed the M diet for 12 weeks (intermediate phase) and lastly fed the V diet (challenge phase) for 6 weeks, generating two dietary regimes (MMV and VMV) across phases. This study used a whole-transcriptome approach to analyse the effects of the V diet at the end of stimulus (short-term effects) and 22 weeks post-first feeding (long-term effects). After the stimulus, due to its developmental stage, the whole intestine was used, whereas, after the challenge, pyloric caeca and middle and distal intestines were examined.

Results and discussion

At the stimulus end, genes with increased expression in V fish enriched pathways including regulatory epigenetic responses and lipid metabolism, and genes involved in innate immune response were downregulated. In the middle intestine at the end of the challenge, expression levels of genes of lipid, carbohydrate, and energy metabolism were increased in V fish, while M fish revealed increased expression of genes associated with autoimmune and acute adaptive immune response. The distal intestine of V fish showed increased expression of genes associated with immune response and potential immune tolerance. Conversely, the distal intestine of M fish at challenge revealed upregulation of lipid and carbohydrate metabolic pathways, tissue degeneration, and apoptotic responses. The present study demonstrated nutritional programming-associated changes in the intestinal transcriptome, with altered expression of genes involved in both immune responses and different metabolic processes. While there were limited changes in growth between the groups, the results show that there were transcriptional differences, suggesting a programming response, although the mechanism of this response still requires to be fully elucidated.

Modulation of gut microbiota composition and predicted metabolic capacity after nutritional programming with a plant-rich diet in Atlantic salmon (Salmo salar): insights across developmental stages

To promote sustainable aquaculture, the formulation of Atlantic salmon (Salmo salar) feeds has changed in recent decades, focusing on replacing standard marine-based ingredients with plant-based alternatives, increasingly demonstrating successful outcomes in terms of fish performance. However, little is known about how these plant-based diets may impact the gut microbiota at first feeding and onwards. Nutritional programming (NP) is one strategy applied for exposing fish to a plant-based (V) diet at an early stage in life to promote full utilisation of plant-based ingredients and prevent potential adverse impacts of exposure to a plant-rich diet later in life. We investigated the impact of NP on gut microbiota by introducing fish to plant ingredients (V fish) during first feeding for a brief period of two weeks (stimulus phase) and compared those to fish fed a marine-based diet (M fish). Results demonstrated that V fish not only maintained growth performance at 16 (intermediate phase) and 22 (challenge phase) weeks post first feeding (wpff) when compared to M fish but also modulated gut microbiota. PERMANOVA general effects revealed gut microbiota dissimilarity by fish group (V vs. M fish) and phases (stimulus vs. intermediate vs. challenge). However, no interaction effect of both groups and phases was demonstrated, suggesting a sustained impact of V diet (nutritional history) on fish across time points/phases. Moreover, the V diet exerted a significant cumulative modulatory effect on the Atlantic salmon gut microbiota at 16 wpff that was not demonstrated at two wpff, although both fish groups were fed the M diet at 16 wpff. The nutritional history/dietary regime is the main NP influencing factor, whereas environmental and host factors significantly impacted microbiota composition in M fish. Microbial metabolic reactions of amino acid metabolism were higher in M fish when compared to V fish at two wpff suggesting microbiota played a role in digesting the essential amino acids of M feed. The excessive mucin O-degradation revealed in V fish at two wpff was mitigated in later life stages after NP, suggesting physiological adaptability and tolerance to V diet. Future studies are required to explore more fully how the microbiota functionally contributes to the NP.

A Pretty Kettle of Fish: A Review on the Current Challenges in Mediterranean Teleost Reproduction

The Mediterranean region is facing several environmental changes and pollution issues. Teleosts are particularly sensitive to these challenges due to their intricate reproductive biology and reliance on specific environmental cues for successful reproduction. Wild populations struggle with the triad of climate change, environmental contamination, and overfishing, which can deeply affect reproductive success and population dynamics. In farmed species, abiotic factors affecting reproduction are easier to control, whereas finding alternatives to conventional diets for farmed teleosts is crucial for enhancing broodstock health, reproductive success, and the sustainability of the aquaculture sector. Addressing these challenges involves ongoing research into formulating specialized diets, optimizing feeding strategies, and developing alternative and sustainable feed ingredients. To achieve a deeper comprehension of these challenges, studies employing model species have emerged as pivotal tools. These models offer advantages in understanding reproductive mechanisms due to their well-defined physiology, genetic tractability, and ease of manipulation. Yet, while providing invaluable insights, their applicability to diverse species remains constrained by inherent variations across taxa and oversimplification of complex environmental interactions, thus limiting the extrapolation of the scientific findings. Bridging these gaps necessitates multidisciplinary approaches, emphasizing conservation efforts for wild species and tailored nutritional strategies for aquaculture, thereby fostering sustainable teleost reproduction in the Mediterranean.

Early nutritional programming in sterlet sturgeon (Acipenser ruthenus) with dietary soybean meal: Assessment of growth performance, body composition, and expression of GH, IGF-I, and Ghrelin genes

This study was performed to assess the impacts of introducing diets containing different levels of soybean meal (SBM) to sterlet sturgeon (Acipenser ruthenus) larvae on growth performance, body composition, and molecular responses in the juvenile stage. The sterlet larvae (57.68 ± 0.66 mg) were weaned onto the formulated diets as follows: a control diet containing 60% fishmeal (FM), and three experimental diets with replacement levels of 15% (SBM15), 30% (SBM30), and 45% (SBM45) of FM with SBM. Then, a total of 260 fish (initial weight: 323.33 ± 11.76 mg) were fed the four different diets for 28 days in triplicates (phase 1, nutritional programming, NP). All treatments were then fed with the FM diet in phase 2 (common phase), and in phase 3 (challenge phase), all experimental groups (6.14 ± 0.08 g) were transitioned to SBM45 for 28 days. At the end of phases 1 and 2, growth performance showed no significant differences among the groups (P > 0.05), while significantly improved in SBM45 than the control at the end of phase 3 (P < 0.05). No significant differences were found among the groups in any phases for whole body composition (P > 0.05). Additionally, the total saturated fatty acids were significantly higher in SBM-based diets than FM at the end of phase 3 (P < 0.05). The mRNA of GH, IGF-I was significantly affected by variation of FM replacement level (P < 0.05). The expression level of Ghrelin was up-regulated in fish fed SBM at the end of phase 3 (P < 0.05). Our findings revealed that NP can positively enhance the adaptation of juvenile sterlet sturgeon to 45% SBM when exposed to the same diets at the larval stage. Further research is being carried out to provide valuable insights into the underlying mechanisms of digestive performance for this species.

Maternal dietary choline levels cause transcriptome shift due to genotype-by-diet interactions in rainbow trout (Oncorhynchus mykiss)

The objective of this study was to identify metabolic regulatory mechanisms affected by choline availability in rainbow trout (Oncorhynchus mykiss) broodstock diets associated with increased offspring growth performance. Three customized diets were formulated to have different levels of choline: (a) 0 % choline supplementation (Low Choline: 2065 ppm choline), (b) 0.6 % choline supplementation (Medium Choline: 5657 ppm choline), and (c) 1.2 % choline supplementation (High Choline: 9248 ppm choline). Six all-female rainbow trout families were fed experimental diets beginning 18 months post-hatch until spawning at 22 months post-hatch; their offspring were fed a commercial diet. Experimental broodstock diet did not affect overall choline, fatty acid, or amino acid content in the oocytes (p > 0.05), apart from tyrosine (p ≤ 0.05). Offspring body weights from the High and Low Choline diets did not differ from those in the Medium Choline diet (p > 0.05); however, family-by-diet and sire-by-diet interactions on offspring growth were detected (p ≤ 0.05). The High Choline diet did not improve growth performance in the six broodstock families at final harvest (520-days post-hatch, or dph). Numerous genes associated with muscle development and lipid metabolism were identified as affected by broodstock diet, including myosin, troponin C, and fatty acid binding proteins, which were associated with key signaling pathways of lipid metabolism, muscle cell development, muscle cell proliferation, and muscle cell differentiation. These findings indicate that supplementing broodstock diets with choline does regulate expression of genes related to growth and nutrient partitioning but does not lead to growth benefits in rainbow trout families selected for disease resistance.

High-fat diet in early life triggers both reversible and persistent epigenetic changes in the medaka fish (Oryzias latipes)

BACKGROUND

The nutritional status during early life can have enduring effects on an animal's metabolism, although the mechanisms underlying these long-term effects are still unclear. Epigenetic modifications are considered a prime candidate mechanism for encoding early-life nutritional memories during this critical developmental period. However, the extent to which these epigenetic changes occur and persist over time remains uncertain, in part due to challenges associated with directly stimulating the fetus with specific nutrients in viviparous mammalian systems.

RESULTS

In this study, we used medaka as an oviparous vertebrate model to establish an early-life high-fat diet (HFD) model. Larvae were fed with HFD from the hatching stages (one week after fertilization) for six weeks, followed by normal chow (NC) for eight weeks until the adult stage. We examined the changes in the transcriptomic and epigenetic state of the liver over this period. We found that HFD induces simple liver steatosis, accompanied by drastic changes in the hepatic transcriptome, chromatin accessibility, and histone modifications, especially in metabolic genes. These changes were largely reversed after the long-term NC, demonstrating the high plasticity of the epigenetic state in hepatocytes. However, we found a certain number of genomic loci showing non-reversible epigenetic changes, especially around genes related to cell signaling, liver fibrosis, and hepatocellular carcinoma, implying persistent changes in the cellular state of the liver triggered by early-life HFD feeding.

CONCLUSION

In summary, our data show that early-life HFD feeding triggers both reversible and persistent epigenetic changes in medaka hepatocytes. Our data provide novel insights into the epigenetic mechanism of nutritional programming and a comprehensive atlas of the long-term epigenetic state in an early-life HFD model of non-mammalian vertebrates.

Available for millions of years but discovered through the last decade: Insects as a source of nutrients and energy in animal diets

The aim of this review is to present and discuss the most recent literature about the processing of insect biomass and its impact on nutritive value, further implementation of meals and fats derived from invertebrates to livestock (poultry and swine), aquaculture (salmonids), and companion animal diets and their impact on growth performance, metabolic response, and gastrointestinal microbiota shifts. Additionally, the most important barriers to obtaining unified products in terms of their nutritive value are considered, i.e., to define insects' nutrient requirements, including various technological groups and further biomass processing (slaughtering, drying, and storage). Due to the current limitation in the insect production process consisting of the lack of infrastructure, there is stress on the relatively small amount of insect products added to the animal diets as a functional feed additive. Currently, only in the case of pet nutrition may insects be considered a full replacement for commonly used environmentally harmful and allergenic products. Simultaneously, the least information has been published on this topic. Thus, more scientific data are needed, particularly when the pet food branch and insect-based diets are rapidly growing.

Nutritional programming of large yellow croaker (Larimichthys crocea) larvae by dietary vegetable oil: effects on growth performance, lipid metabolism and antioxidant capacity

The nutritional status experienced in the early development of life plays a vital role in the long-term metabolic state of the individual, which is known as nutritional programming. The present study investigated the long-term effects of vegetable oil (VO) nutritional programming during the early life of large yellow croaker. First, larvae were fed either a fish oil (FO) diet or a VO diet for 30 d. Subsequently, under the same conditions, all fish were fed a commercial diet for 90 d and thereafter challenged with an FO or VO diet for 30 d. The results showed that growth performance was significantly lower in larvae fed the VO diet than in those in fed the FO diet in the stimulus phase. Notably, VO nutritional history fish showed lower levels of liver lipids liver total triglycerides and serum nonesterified free fatty acids than the FO nutritional history fish when juveniles were challenged with the VO diet, which was consistent with the expression of lipogenesis-related genes and proteins. Moreover, the VO nutritional history fish showed lower liver damage and higher antioxidant capacity than FO nutritional history fish when challenged with the VO diet. In summary, this study showed that a short VO stimulus during the early life stage of large yellow croaker, had a long-term effect on lipid metabolism and the antioxidant system. Specifically, VO nutritional programming had a positive effect on alleviating abnormal lipid deposition on the liver, liver damage, and the reduction of hepatic antioxidant capacity caused by a VO diet.

Effect of micro-algae Schizochytrium sp. supplementation in plant diet on reproduction of female rainbow trout (Oncorhynchus mykiss): maternal programming impact of progeny

Background

The broodstock diet, and in particular the lipid and fatty acid composition of the diet, is known to play a key role in reproductive efficiency and survival of the progeny in fish. A major problem when replacing both fish meal and fish oil by plant sources is the lack of n-3 long chain polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). To address this problem, we studied the effect of the plant-based diet supplemented with Schizochytrium sp. microalgae, source of DHA, compared to a conventional commercial diet rich in fish meal and fish oil on reproductive performance and egg quality and the consequences on progeny, in female rainbow trout broodstock.

Results

The results demonstrated that DHA-rich microalgae supplementation in a plant-based diet allowed for the maintenance of reproductive performance and egg quality comparable to a conventional commercial feed rich in fish meal and fish oil and led to an increased significant fry survival after resorption. Moreover, when females were fed a plant-based diet supplemented with micro-algae, the 4-month-old progenies showed a significant higher growth when they were challenged with a similar diet as broodstock during 1 month. We provide evidence for metabolic programming in which the maternal dietary induced significant protracted effects on lipid metabolism of progeny.

Conclusions

The present study demonstrates that supplementation of a plant-based diet with DHA-rich microalgae can be an effective alternative to fish meal and fish oil in rainbow trout broodstock aquafeed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00680-9.

Nutritional Programming with Dietary Soybean Meal and Its Effect on Gut Microbiota in Zebrafish (Danio rerio)

Nutritional programming (NP) is considered a promising approach that can counteract the negative effects of dietary plant protein (PP) by introducing PP to fish in the early developmental stages. Therefore the objective of our study was to assess the effect of NP on PP utilization and the gut microbiome in zebrafish Danio rerio. The study included four treatment groups: (1) a positive control group that received a fishmeal (FM) diet throughout the entire trial (+ control); (2) a negative control group that received PP diet throughout the entire trial (- control); (3) an NP group that received dietary PP during the larval stage followed by FM-based diet during the juvenile stage and PP diet again during a PP challenge in the grow-out phase (NP-PP); and (4) an FM-group that received FM-based diet during the larval and juvenile stages and was challenged with a PP diet during the grow-out phase (NP-FM). During the PP challenge, the NP-PP group achieved the highest weight gain compared to the (-) control and NP-FM groups. The relative abundance of certain phyla such as Chloroflexi, Planctomycetes, and Bacteroidetes presented higher values in some groups at early juvenile stage. The fish gut microbiome also presented differences throughout the study.

Digestive tract morphology and enzyme activities of juvenile diploid and triploid Atlantic salmon (Salmo salar) fed fishmeal-based diets with or without fish protein hydrolysates

Triploid, sterile Atlantic salmon (Salmo salar) could make a contribution to the development of the farming industry, but uncertainties about the performance and welfare of triploids have limited their adoption by farmers. In this study, we compared the ontogeny of digestive tract morphology and enzyme activities (pepsin, trypsin, chymotrypsin, alkaline phosphatase and aminopeptidase) of diploid and triploid Atlantic salmon. Fish were fed diets based on fishmeal (STD) or a mix of fishmeal and hydrolysed fish proteins (HFM) whilst being reared at low temperature from start-feeding to completion of the parr-smolt transformation. Fish weights for each ploidy and feed combination were used to calculate thermal growth coefficients (TGCs) that spanned this developmental period, and the data were used to examine possible relationships between enzyme activities and growth. At the end of the experiment, faeces were collected and analyzed to determine the apparent digestibility coefficients (ADCs) of the dietary amino acids (AAs). Digestive tract histo-morphology did not differ substantially between ploidies and generally reflected organ maturation and functionality. There were no consistent differences in proteolytic enzyme activities resulting from the inclusion of HFM in the diet, nor was there improved digestibility and AA bioavailability of the HFM feed in either diploid or triploid fish. The triploid salmon had lower ADCs than diploids for most essential and non-essential AAs in both diets (STD and HFM), but without there being any indication of lower intestinal protease activity in triploid fish. When trypsin-to-chymotrypsin activity and trypsin and alkaline phosphatase (ALP) ratios (T:C and T:ALP, respectively) were considered in combination with growth data (TGC) low T:C and T:ALP values coincided with times of reduced fish growth, and vice versa, suggesting that T:C and T:ALP may be used to predict recent growth history and possible growth potential.

Parental LC-PUFA biosynthesis capacity and nutritional intervention with alpha-linolenic acid affect performance of Sparus aurata progeny

Environmental factors such as nutritional interventions during early developmental stages affect and establish long-term metabolic changes in all animals. Diet during the spawning period has a nutritional programming effect in offspring of gilthead seabream 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 to limitations in the pre-formed products, n-3 LC-PUFA, contained in the diets used during nutritional programming. This study investigated the combined effects of nutritional programming on Sparus aurata through broodstock diets during the spawning period and in broodfish showing higher or lower fads2 expression levels in the blood after 1 month of 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 spawning quality parameters as well as in the growth of 6 month 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 also an excellent option for tailoring and increasing the flesh n-3 LC-PUFA levels to meet the recommended dietary allowances for human consumption.

Early feeding with hyperglucidic diet during fry stage exerts long-term positive effects on nutrient metabolism and growth performance in adult tilapia (Oreochromis niloticus)

The present study aimed to investigate nutritional programming of carbohydrate metabolism in Nile tilapia. Early nutritional intervention stimulus was achieved by feeding fry with high-protein/low-carbohydrate (HP/LC) or low-protein/high-carbohydrate (LP/HC) diet since first feeding for 4 weeks, and the effect of nutritional stimulus on carbohydrate and its related metabolism was evaluated through the adult stage. Our findings indicated that at week 1, LP/HC diet-fed fry had lower levels of mRNA for genes coding gluconeogenesis and amino acid catabolism and higher levels of hk2 (P < 0⋅05). As expected, in adult tilapia, although LP/HC diet-fed fish had poorer growth (end of stimulus), the fish showed compensatory growth. There were permanent effects of early high-carbohydrate (HC) intake on several parameters, including (1) modulating hepatic composition, (2) increased muscle glycogen, (3) lower levels of enzymes involved in amino acid catabolism and (4) higher levels of glycolytic enzymes in glycolysis. Finally, HP/LC diet- and LP/HC diet-fed fish were challenged with different dietary carbohydrate levels. Irrespective of challenging diets, the early HC stimulus had significant effects on adult tilapia by (1) promoting utilisation of glucose, which had protein-sparing effects for better growth, (2) inducting lipogenesis and (3) decreasing amino acid catabolism. Taken together, for the first time, we demonstrated that early HC feeding was effective for positive nutritional programming of metabolism in Nile tilapia (an omnivorous fish). It led to the improvement of growth performance in adult fish associated with early feeding, which is linked to a better ability to use glucose, to induce lipogenesis, and to suppress amino acid catabolism.

Comparative transcriptomics reveals domestication-associated features of Atlantic salmon lipid metabolism

Domestication of animals imposes strong targeted selection for desired traits but can also result in unintended selection due to new domestic environments. Atlantic salmon (Salmo salmar) was domesticated in the 1970s and has subsequently been selected for faster growth in systematic breeding programmes. More recently, salmon aquaculture has replaced fish oils (FOs) with vegetable oils (VOs) in feed, radically changing the levels of essential long-chain polyunsaturated fatty acids (LC-PUFAs). Our aim here was to study the impact of domestication on metabolism and explore the hypothesis that the shift to VO diets has unintentionally selected for a domestication-specific lipid metabolism. We conducted a 96-day feeding trial of domesticated and wild salmon fed diets based on FOs, VOs or phospholipids, and compared transcriptomes and fatty acids in tissues involved in lipid absorption (pyloric caeca) and lipid turnover and synthesis (liver). Domesticated salmon had faster growth and higher gene expression in glucose and lipid metabolism compared to wild fish, possibly linked to differences in regulation of circadian rhythm pathways. Only the domesticated salmon increased expression of LC-PUFA synthesis genes when given VOs. This transcriptome response difference was mirrored at the physiological level, with domesticated salmon having higher LC-PUFA levels but lower 18:3n-3 and 18:2n-6 levels. In line with this, the VO diet decreased growth rate in wild but not domesticated salmon. Our study revealed a clear impact of domestication on transcriptomic regulation linked to metabolism and suggests that unintentional selection in the domestic environment has resulted in evolution of stronger compensatory mechanisms to a diet low in LC-PUFAs.

Glucose Injection Into Yolk Positively Modulates Intermediary Metabolism and Growth Performance in Juvenile Nile Tilapia (Oreochromis niloticus)

The aim of this study was to explore for the first time in omnivorous fish the concept of nutritional programming. A nutritional stimulus was accomplished by microinjecting 2 M glucose into yolk reserves during the alevin stage in Nile tilapia (Oreochromis niloticus). At the molecular level in fry, at 1 week post-injection, glucose stimuli were associated with the up-regulation of genes involved in glycolysis (pklr, hk1, hk2, and pkma), glucose transport (glut4) pathways and down-regulation of genes related to gluconeogenesis (g6pca1, g6pca2, and pck1) and amino acid catabolism (asat, alat) (P < 0.05), demonstrating that the larvae well received the glucose stimulus at a molecular level. Moreover, 20 weeks after glucose injection, early glucose stimuli were always linked to permanent effects in juvenile fish, as reflected by a higher level of glycolytic enzymes [gck, hk1 and hk2 at both mRNA and enzymatic levels and pyruvate kinase (PK) activity]. Finally, the effects of the glucose stimulus history were also examined in fish fed with two different dietary carbohydrate/protein levels (medium-carbohydrate diet, CHO-M; high-carbohydrate diet, CHO-H) in juvenile fish (during weeks 20-24). As expected, the CHO-H diet induced the expression of glycolytic and lipogenic genes (gck, pklr, hk1, hk2, fpkma, fasn, and g6pd) and suppressed the expression of gluconeogenic and amino acid catabolism genes (g6pca1, pck1, pck2, asat, alat, and gdh). Nevertheless, the early glucose stimulus led to persistent up-regulation of glycolytic enzymes (gck, pklr, hk1, and hk2) at both the mRNA and enzyme activity levels and glucose transporter glut4 as well as lower gluconeogenic pck1 gene expression (P < 0.05). More interestingly, the early glucose stimulus was associated with a better growth performance of juvenile fish irrespective of the diets. These permanent changes were associated with DNA hypomethylation in the liver and muscles, suggesting the existence of epigenetic mechanisms at the origin of programming. In conclusion, for the first time in tilapia, early glucose stimuli were found to be clearly associated with a positive metabolic programming effect later in life, improving the growth performance of the fish.

New Insights on Intermediary Metabolism for a Better Understanding of Nutrition in Teleosts

The rapid development of aquaculture production throughout the world over the past few decades has led to the emergence of new scientific challenges to improve fish nutrition. The diet formulations used for farmed fish have been largely modified in the past few years. However, bottlenecks still exist in being able to suppress totally marine resources (fish meal and fish oil) in diets without negatively affecting growth performance and flesh quality. A better understanding of fish metabolism and its regulation by nutrients is thus mandatory. In this review, we discuss four fields of research that are highly important for improving fish nutrition in the future: ( a) fish genome complexity and subsequent consequences for metabolism, ( b) microRNAs (miRNAs) as new actors in regulation of fish metabolism, ( c) the role of autophagy in regulation of fish metabolism, and ( d) the nutritional programming of metabolism linked to the early life of fish.

DNA methylation of the promoter region of bnip3 and bnip3l genes induced by metabolic programming

BACKGROUND

Environmental changes of biotic or abiotic nature during critical periods of early development may exert a profound influence on physiological functions later in life. This process, named developmental programming can also be driven through parental nutrition. At molecular level, epigenetic modifications are the most likely candidate for persistent modulation of genes expression in later life.

RESULTS

In order to investigate epigenetic modifications induced by programming in rainbow trout, we focused on bnip3 and bnip3l paralogous genes known to be sensitive to environmental changes but also regulated by epigenetic modifications. Two specific stimuli were used: (i) early acute hypoxia applied at embryo stage and (ii) broodstock and fry methionine deficient diet, considering methionine as one of the main methyl-group donor needed for DNA methylation. We observed a programming effect of hypoxia with an increase of bnip3a and the four paralogs of bnip3l expression level in fry. In addition, parental methionine nutrition was correlated to bnip3a and bnip3lb1 expression showing evidence for early fry programming. We highlighted that both stimuli modified DNA methylation levels at some specific loci of bnip3a and bnip3lb1.

CONCLUSION

Overall, these data demonstrate that methionine level and hypoxia stimulus can be of critical importance in metabolic programming. Both stimuli affected DNA methylation of specific loci, among them, an interesting CpG site have been identified, namely - 884 bp site of bnip3a, and may be positively related with mRNA levels.

Comparisons of reproductive function and fatty acid fillet quality between triploid and diploid farm Atlantic salmon (Salmo salar)

Triploidy could prevent escaped farm salmon breeding in the wild, while also improving nutrient quality within farmed fillets. Despite these potential advantages, triploid Atlantic salmon have not been widely used in aquaculture, and their reproductive function has yet to be fully evaluated. Here, we compare reproductive function and fillet composition between triploid and diploid farm salmon under standard aquaculture rearing conditions. We show that female triploids are sterile and do not develop gonads. By contrast, males produce large numbers of motile spermatozoa capable of fertilizing wild salmon eggs. However, compared with diploids, reproductive development and survival rates of eggs fertilized by triploid males were significantly reduced, with less than 1% of eggs sired by triploid males reaching late-eyed stages of development. Analyses of fillets showed that total lipid and fatty acid quantities were significantly lower in triploid than in diploid Atlantic salmon fillets. However, when fatty acids were normalized to total lipid content, triploid fillets had significantly higher relative levels of important omega-3 long-chain polyunsaturated fatty acids. Our results show that: (i) escaped triploid farm salmon are very unlikely to reproduce in the wild and (ii) if able to match diploid fillet lipid content, triploid farm salmon could achieve better fillet quality in terms of essential fatty acids.

Early nutritional programming affects liver transcriptome in diploid and triploid Atlantic salmon, Salmo salar

BACKGROUND

To ensure sustainability of aquaculture, plant-based ingredients are being used in feeds to replace marine-derived products. However, plants contain secondary metabolites which can affect food intake and nutrient utilisation of fish. The application of nutritional stimuli during early development can induce long-term changes in animal physiology. Recently, we successfully used this approach to improve the utilisation of plant-based diets in diploid and triploid Atlantic salmon. In the present study we explored the molecular mechanisms occurring in the liver of salmon when challenged with a plant-based diet in order to determine the metabolic processes affected, and the effect of ploidy.

RESULTS

Microarray analysis revealed that nutritional history had a major impact on the expression of genes. Key pathways of intermediary metabolism were up-regulated, including oxidative phosphorylation, pyruvate metabolism, TCA cycle, glycolysis and fatty acid metabolism. Other differentially expressed pathways affected by diet included protein processing in endoplasmic reticulum, RNA transport, endocytosis and purine metabolism. The interaction between diet and ploidy also had an effect on the hepatic transcriptome of salmon. The biological pathways with the highest number of genes affected by this interaction were related to gene transcription and translation, and cell processes such as proliferation, differentiation, communication and membrane trafficking.

CONCLUSIONS

The present study revealed that nutritional programming induced changes in a large number of metabolic processes in Atlantic salmon, which may be associated with the improved fish performance and nutrient utilisation demonstrated previously. In addition, differences between diploid and triploid salmon were found, supporting recent data that indicate nutritional requirements of triploid salmon may differ from those of their diploid counterparts.

Parental nutritional programming and a reminder during juvenile stage affect growth, lipid metabolism and utilisation in later developmental stages of a marine teleost, the gilthead sea bream (Sparus aurata)

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 : 4n-3, 18 : 3n-6, 20 : 5n-3, 22 : 6n-3 and 22 : 5n-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.