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The present study aims to investigate nutritional programming through early starvation in the European seabass (Dicentrarchus labrax). European seabass larvae were fasted at three different developmental periods for three durations from 60 to 65 dph (F1), 81 to 87 dph (F2), and 123 to 133 dph (F3). Immediate effects were investigated by studying gene expression of npy (neuropeptide Y) and avt (Arginine vasotocin) in the head, while potential long-term effects (i.e., programming) were evaluated on intermediary metabolism later in life (in juveniles). Our findings indicate a direct effect regarding gene expression in the head only for F1, with higher avt mRNA level in fasted larved compared to controls. The early starvation periods had no long-term effect on growth performance (body weight and body length). Regarding intermediary metabolism, we analyzed related key plasma metabolites which reflect the intermediary metabolism: no differences for glucose, triglycerides, and free fatty acids in the plasma were observed in juveniles irrespective of the three early starvation stimuli. As programming is mainly linked to molecular mechanisms, we then studied hepatic mRNA levels for 23 key actors of glucose, lipid, amino acid, and energy metabolism. For many of the metabolic genes, there was no impact of early starvation in juveniles, except for three genes involved in glucose metabolism (glut2-glucose transporter and pk-pyruvate kinase) and lipid metabolism (acly-ATP citrate lyase) which were higher in F2 compared to control. Together, these results highlight that starvation between 81 to 87 dph may have more long-term impact, suggesting the existence of a developmental window for programming by starvation. In conclusion, European seabass appeared to be resilient to early starvation during larvae stages without drastic impacts on intermediary metabolism later in life., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Efficient utilisation of plant-based diets in the giant freshwater prawn, Marcrobrachium rosenbergii, varies according to individual, suggesting that it might be associated with differences in physiological and metabolic responses. Therefore, we aimed to investigate the individual differences in the growth response of shrimp fed to a soybean-based diet (SBM). Two hundred shrimp were fed SBM for 90 days, and specific growth rate (SGR) was determined individually. Fast- and slow-growing shrimp (F-shrimp vs. S-shrimp), with the highest and lowest 5% SGRs, respectively, were sampled to determine haemolymph chemistry and carcass composition. The hepatopancreas of these shrimps were used for transcriptome analysis through RNA sequencing (RNA-Seq). The results showed no significant differences in haemolymph chemistry parameters. In terms of carcass proximate composition, F-shrimp exhibited higher protein composition than did S-shrimp, suggesting that F-shrimp have higher protein anabolism. Using RNA-seq and real-time reverse transcription polymerase chain reaction (qRT-PCR), the expression levels of several genes encoding physiologic and metabolic enzymes were found to be upregulated in F-shrimp compared to in S-shrimp, suggesting that these enzymes/proteins mediated the efficient use of SBM-based diets for growth promotion in shrimp. Various DEGs associated with the immune system were observed, indicating a difference in immune processes between F- and S-shrimp. The expression of several housekeeping genes was found to be upregulated in S-shrimp. Collectively, the upregulated expression of several enzymes associated with physiological and/or metabolic processes and increased protein anabolism may be attributed to the efficient use of SBM for maximal growth in shrimp., (© 2024. The Author(s).)

Background: High dietary carbohydrates can spare protein in rainbow trout (Oncorhynchus mykiss) but may affect growth and health. Inulin, a prebiotic, could have nutritional and metabolic effects, along with anti-inflammatory properties in teleosts, improving growth and welfare. We tested this hypothesis in rainbow trout by feeding them a 100% plant-based diet, which is a viable alternative to fishmeal and fish oil in aquaculture feeds. In a two-factor design, we examined the impact of inulin (2%) as well as the variation in the carbohydrates (CHO)/plant protein ratio on rainbow trout. We assessed the influence of these factors on zootechnical parameters, plasma metabolites, gut microbiota, production of short-chain fatty acids and lactic acid, as well as the expression of free-fatty acid receptor genes in the mid-intestine, intermediary liver metabolism, and immune markers in a 12-week feeding trial., Results: The use of 2% inulin did not significantly change the fish intestinal microbiota, but interestingly, the high CHO/protein ratio group showed a change in intestinal microbiota and in particular the beta diversity, with 21 bacterial genera affected, including Ralstonia, Bacillus, and 11 lactic-acid producing bacteria. There were higher levels of butyric, and valeric acid in groups fed with high CHO/protein diet but not with inulin. The high CHO/protein group showed a decrease in the expression of pro-inflammatory cytokines (il1b, il8, and tnfa) in liver and a lower expression of the genes coding for tight-junction proteins in mid-intestine (tjp1a and tjp3). However, the 2% inulin did not modify the expression of plasma immune markers. Finally, inulin induced a negative effect on rainbow trout growth performance irrespective of the dietary carbohydrates., Conclusions: With a 100% plant-based diet, inclusion of high levels of carbohydrates could be a promising way for fish nutrition in aquaculture through a protein sparing effect whereas the supplementation of 2% inulin does not appear to improve the use of CHO when combined with a 100% plant-based diet., (© 2024. The Author(s).)

Short-term adaptation of the microbiota could promote nutrient degradation and the host health. While numerous studies are currently undertaking feeding trials using sustainable diets for the aquaculture industry, the extent to which the microbiota adapts to these novel diets is poorly described. The incorporation of carbohydrates (CHO) within a 100% plant-based diet could offer a novel, cost-effective energy source that is readily available, potentially replacing the protein component in the diets. In this study, we investigated the short-term (3 weeks) effects of a high CHO, 100% plant-based diet on the mucosal and digesta associated microbiota diversity and composition, as well as several metabolic parameters in rainbow trout. We highlighted that the mucosa is dominated by Mycoplasma (44.86%). While the diets did not have significant effects on the main phyla (Proteobacteria, Firmicutes, and Actinobacteria), after 3 weeks, a lower abundance of Bacillus genus, and higher abundances of four lactic-acid bacteria were demonstrated in digesta. In addition, no post-prandial hyperglycemia was observed with high carbohydrate intake. These results provide evidence for the rapid adaptation of the gut microbiota and host metabolism to high CHO in combination with 100% plant ingredients in rainbow trout., (© The Author(s) 2024. Published by Oxford University Press on behalf of FEMS.)

Inulin affects nutrition and metabolism in many animals. Although inulin is widely used in the diet of teleosts, its mechanism of action is unknown. Here, we investigated the effect of inulin (2 %) on the intestinal microbiome and metabolism in rainbow trout ( Oncorhynchus mykiss ) selected for growth and survival when fed a 100 % plant-based diet ( suave ) and a control line ( temoin ). Metabolic responses to the two factors (line and inulin) in liver, intestine, muscle and adipose were tissue-specific, with line and interaction between the two factors influencing overall expression in liver. In the intestine, inulin and line and in muscle, line influenced the expression of metabolic genes. Microbiota between the mucus and digestive contents was significantly different, with genera from Proteobacteria being more abundant in the mucus, whereas genera from the Firmicutes and Planctomycetes being more abundant in contents. Effect of inulin and interaction between factors on the microbiome was evident in contents. The significant taxa of control and inulin-fed groups differed greatly with Streptococcus and Weissella being significantly abundant in the inulin-fed group. There was a general trend showing higher levels of all SCFA in temoin group with propionic acid levels being significantly higher. An operational taxonomic unit (OTU) belonging to the Ruminococcaceae was significantly abundant in suave . The tissue-specific correlations between OTU and gene expression may indicate the link between microbiome and metabolism. Together, these results suggest that line and inulin impact the gene expression in a tissue-specific manner, possibly driven by specific OTUs enriched in inulin-fed groups and suave .

Rainbow trout (Oncorhynchus mykiss) is traditionally considered as a poor user of digestible carbohydrates harbouring persistent postprandial hyperglycaemia and decreased growth performances when fed a diet containing more than 20% of digestible carbohydrates. While this glucose-intolerant phenotype is well-described in juveniles, evidence points to a particular regulation of glucose metabolism in rainbow trout broodstrocks. By detecting changes in glucose levels and triggering a specific metabolic response, the hypothalamus plays a key role in the regulation of peripheral glucose metabolism. Therefore, our objective was to assess, for the first time in fish, the short-term consequences in hypothalamus, the glucose sensing and feed intake regulation of feeding mature female and male, and neomale rainbow trout with a diet containing either no or a 33% carbohydrate. The hypothalamic glucosensing capacity was assessed through mRNA levels of glucosensing related-genes and feed intake regulation through appetite-regulating peptides. Our data indicate that a brief period of carbohydrate intake (5 meals at 8 °C) did not induce specific changes in glucosensing capacity and appetite-regulating peptides in the hypothalamus of rainbow trout broodstock. Our results did however demonstrate, for the first time in fish, the existence of sex dimorphism of glucosensing-related genes and appetite-regulating peptides., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

This study investigated the influence of dietary astaxanthin (AX) on glucose and lipid metabolism in rainbow trout liver. Two iso-nitrogenous and iso-lipidic diets were tested for 12 weeks in rainbow trout with an initial mean weight of 309 g. The S-ASTA diet was supplemented with 100 mg of synthetic AX per kg of feed, whereas the control diet (CTRL) had no AX. Fish fed the S-ASTA diet displayed lower neutral and higher polar lipids in the liver, associated with smaller hepatocytes and lower cytoplasm vacuolization. Dietary AX upregulated adipose triglyceride lipase ( atgl ), hormone-sensitive lipase ( hsl2 ) and 1,2-diacylglycerol choline phosphotransferase ( chpt ), and downregulated diacylglycerol acyltransferase ( dgat2 ), suggesting the AX's role in triacylglycerol (TAG) turnover and phospholipid (PL) synthesis. Dietary AX may also affect beta-oxidation with the upregulation of carnitine palmitoyltransferase 1 ( cpt1α2 ). Although hepatic cholesterol levels were not affected, dietary AX increased gene expression of sterol regulatory element-binding protein 2 ( srebp2 ). Dietary AX upregulated the expression of 6-phosphogluconate dehydrogenase ( 6pgdh ) and downregulated pyruvate kinase ( pkl ). Overall, results suggest that dietary AX modulates the oxidative phase of the pentose phosphate pathway and the last step of glycolysis, affecting TAG turnover, β-oxidation, PL and cholesterol synthesis in rainbow trout liver.

An increase in egg incubation temperature was previously shown to enhance the metabolism of mule ducks and increase liver fattening after overfeeding, through a metabolic programming mechanism. Here, we examined whether fasting (F) followed by refeeding (RF) in 11-wk-old mule ducks could become an accelerated model to study the mechanisms of metabolic programming following embryonic thermal manipulation. This study investigated the hepatic response of mule ducks subjected to 23 h of fasting and 1 h of refeeding, in control or thermally programmed animals (with an increase of 1°C, 16 h per day from days 13 to 27 of embryogenesis). Liver weight and energy composition, hepatocyte structure, plasma parameters, and gene expression levels were measured at 1, 2, and 4 h after RF. All these parameters were strongly affected by RF, whereas significant impacts of embryonic programming were measured in cell size (+1 µm on average), lipid composition (+4.2% of saturated fatty acids 4 h after the meal), and relative gene expressions (including HK1 , SCD1 , ELOVL6 , and FASN ). In addition to confirming previously identified molecular targets of thermal manipulation, this study revealed new ones, thanks to kinetic sampling after RF. Finally, the detailed description of the impact of the F/RF challenge on the liver structure, composition, and gene expression, but also on plasma parameters allowed us to draw a parallel with these same traits measured during overfeeding. This comparative analysis suggests that this protocol could become a pertinent model to study the mechanisms involved in embryonic liver thermal programming, without overfeeding.

Stresses associated with changes in diet or environmental disturbances are common situations that fish encounter during their lifetime. The stability and ease of measuring microRNAs (miRNAs) present in biological fluids make these molecules particularly interesting biomarkers for non-lethal assessment of stress in animals. Rainbow trout were exposed for four weeks to abiotic stress (moderate hypoxia) and/or nutritional stress (a high-carbohydrate/low-protein diet). Blood plasma and epidermal mucus were sampled at the end of the experiment, and miRNAs were assessed using small RNA sequencing. We identified four miRNAs (miR-122-5p, miR-184-3p, miR-192-5p and miR-194a-5p) and three miRNAs (miR-210-3p, miR-153a-3p and miR-218c-5p) that accumulated in response to stress in blood plasma and epidermal mucus, respectively. In particular, the abundance of miR-210-3p, a hypoxamiR in mammals, increased strongly in the epidermal mucus of rainbow trout subjected to moderate hypoxia, and can thus be considered a relevant biomarker of hypoxic stress in trout. We explored the contribution of 22 tissues/organs to the abundance of circulating miRNAs (c-miRNAs) in blood plasma and epidermal mucus influenced by the treatments. Some miRNAs were tissue-specific, while others were distributed among several tissues. Some c-miRNAs (e.g., miR-210-3p, miR184-3p) showed similar variations in both tissues and fluids, while others showed an inverse trend (e.g., miR-122-5p) or no apparent relationship (e.g. miR-192-5p, miR-194a-5p. Overall, these results demonstrate that c-miRNAs can be used as non-lethal biomarkers to study stress in fish. In particular, the upregulation of miR-210-3p in epidermal mucus induced by hypoxia demonstrates the potential of using epidermal mucus as a matrix for identifying non-invasive biomarkers of stress. This study provides information about the tissue sources of c-miRNAs and highlights the potential difficulty in relating variations in miRNA abundance in biological fluids to that in tissues., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

It is now recognised that parental diets could alter their offspring metabolism, concept known as nutritional programming. For agronomic purposes, it has been previously proposed that programming could be employed as a strategy to prepare individual for future nutritional challenges. Concerning cultured fish that belong to high trophic level, plant-derived carbohydrates are a possible substitute for the traditional protein-rich fishmeal in broodstock diet, lowering thus the dietary protein-to-carbohydrate ratio (HC/LP nutrition). However, in mammals, numerous studies have previously demonstrated that parental HC/LP nutrition negatively affects their offspring in the long term. Therefore, the question of possible adaptation to plant-based diets, via parental nutrition, should be explored. First, the maternal HC/LP nutrition induced a global DNA hypomethylation in the liver of their offspring. Interestingly at the gene expression level, the effects brought by the maternal and paternal HC/LP nutrition cumulated in the liver, as indicated by the altered transcriptome. The paternal HC/LP nutrition significantly enhanced cholesterol synthesis at the transcriptomic level. Furthermore, hepatic genes involved in long-chain polyunsaturated fatty acids were significantly increased by the parental HC/LP nutrition, affecting thus both hepatic and muscle fatty acid profiles. Overall, the present study demonstrated that lipid metabolism could be modulated via a parental nutrition in rainbow trout, and that such modulations have consequences on their progeny phenotypes., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)

Reproductive performances, and the factors affecting them, are of major importance especially for farmed fish in the context of the development of a sustainable aquaculture. Dietary maternal lipids have been identified as a major factor affecting reproductive performances. Nevertheless, the consequences of carbohydrates have been little studied while plant-derived carbohydrates could be increasingly used in broodstock diets. To explore this issue, 2-year-old female trout were fed either a control diet that contains no carbohydrate and a high protein content (65.7%) or a diet formulated with plant-derived carbohydrates containing 32.5% carbohydrate and 42.9% protein ('HC diet') for an entire reproductive cycle. The reproductive performances, the quality of the unfertilized eggs and the development of the progeny were carefully monitored. Although the one year HC nutrition had not impaired female growth nor spawns quality, such nutrition had increased the variability of eggs size within spawns (+ 34.0%). Moreover, the eggs produced had a modified fatty acid profile, including a significant reduction in EPA content (- 22.9%) and a significant increase in the AA/EPA ratio (+ 33.3%). The progeny were impacted by such alterations as their survival rates were significantly reduced. A lower plant-derived carbohydrate inclusion (20%) should be considered in aquafeed for female broodstock in trout., (© 2022. The Author(s).)

Background: A high carbohydrate-low protein diet can induce hepatic global DNA hypomethylation in trout. The mechanisms remain unclear., Objectives: We aimed to investigate whether an increase in dietary carbohydrates (dHCs) or a decrease in dietary proteins (dLPs) can cause hepatic global DNA hypomethylation, as well as explore the underlying mechanisms in trout., Methods: Two feeding trials were conducted on juvenile males, both of which involved a 4-d fasting and 4-d refeeding protocol. In trial 1, trout were fed either a high protein-no carbohydrate [HP-NC, protein 60% dry matter (DM), carbohydrates 0% DM] or a moderate protein-high carbohydrate (MP-HC, protein 40% DM, carbohydrates 30% DM) diet. In trial 2, fish were fed either a moderate protein-no carbohydrate (MP-NC, protein 40% DM, carbohydrates 0% DM), an MP-HC (protein 40% DM, carbohydrates 30% DM), or a low protein-no carbohydrate (LP-NC, protein 20% DM, carbohydrates 0% DM) diet to separate the effects of dHCs and dLPs on the hepatic methylome. Global CmCGG methylation, DNA demethylation derivative concentrations, and mRNA expression of DNA (de)methylation-related genes were measured. Differences were tested by 1-factor ANOVA when data were normally distributed or by Kruskal-Wallis nonparametric test if not., Results: In both trials, global CmCGG methylation concentrations remained unaffected, but the hepatic 5-mdC content decreased after refeeding (1-3%). The MP-HC group had 3.4-fold higher hepatic 5-hmdC and a similar 5-mdC concentration compared with the HP-NC group in trial 1. Both MP-HC and LP-NC diets lowered the hepatic 5-mdC content (1-2%), but only the LP-NC group had a significantly lower 5-hmdC concentration (P < 0.01) compared with MP-NC group in trial 2., Conclusions: dHC and dLP independently induced hepatic global DNA demethylation in trout. The alterations in other methylation derivative concentrations indicated the demethylation process was achieved through an active demethylation pathway and probably occurred at non-CmCGG sites., (© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society for Nutrition.)

Embryonic thermal programming has been shown to improve foie gras production in overfed mule ducks. However, the mechanisms at the origin of this programming have not yet been characterized. In this study, we investigated the effect of embryonic thermal manipulation (+1°C, 16 h/24 h from embryonic (E) day 13 to E27) on the hepatic expression of genes involved in lipid and carbohydrate metabolisms, stress, cell proliferation and thyroid hormone pathways at the end of thermal manipulation and before and after overfeeding (OF) in mule ducks. Gene expression analyses were performed by classic or high throughput real-time qPCR. First, we confirmed well-known results with strong impact of OF on the expression of genes involved in lipid and carbohydrates metabolisms. Then we observed an impact of OF on the hepatic expression of genes involved in the thyroid pathway, stress and cell proliferation. Only a small number of genes showed modulation of expression related to thermal programming at the time of OF, and only one was also impacted at the end of the thermal manipulation. For the first time, we explored the molecular mechanisms of embryonic thermal programming from the end of heat treatment to the programmed adult phenotype with optimized liver metabolism., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Massimino, Andrieux, Biasutti, Davail, Bernadet, Pioche, Ricaud, Gontier, Morisson, Collin, Panserat and Houssier.)