Three-year breeding cycle of rainbow trout (Oncorhynchus mykiss) fed a plant-based diet, totally free of marine resources: consequences for reproduction, fatty acid composition and progeny survival

Gut physiology of rainbow trout (Oncorhynchus mykiss) is influenced more by short-term fasting followed by refeeding than by feeding fishmeal-free diets

Supplementing a fishmeal-free diet with yeast extract improves rainbow trout (Oncorhynchus mykiss) growth performance and modulates the hepatic and intestinal transcriptomic response. These effects are often observed in the long term but are not well documented after short periods of fasting. Fasting for a few days is a common practice in fish farming, especially before handling the fish, such as for short sorting, tank transfers, and vaccinations. In the present study, rainbow trout were subjected to a 4-day fast and then refed, for 8 days, a conventional diet containing fishmeal (control diet) or alternative diets composed of terrestrial animal by-products supplemented or not with a yeast extract. During the refeeding period alone, most of the parameters considered did not differ significantly in response to the different feeds. Only the expression of claudin-15 was upregulated in fish fed the yeast-supplemented diet compared to the control diet. Conversely, fasting followed by refeeding significantly influenced most of the parameters analyzed. In the proximal intestine, the surface area of villi significantly increased, and the density of goblet cell tended to decrease during refeeding. Although no distinct plasma immune response or major signs of gut inflammation were observed, some genes involved in the structure, complement pathway, antiviral functions, coagulation, and endoplasmic reticulum stress response of the liver and intestine were significantly regulated by refeeding after fasting. These results indicate that short-term fasting, as commonly practiced in fish farming, significantly alters the physiology of the liver and intestine regardless of the composition of the diet.

Adverse effects of excessive dietary arachidonic acid on survival, PUFA-derived enzymatic and non-enzymatic oxylipins, stress response in rainbow trout fry

Arachidonic acid (C20: 4n-6, AA) plays a fundamental role in fish physiology, influencing growth, survival and stress resistance. However, imbalances in dietary AA can have detrimental effects on fish health and performance. Optimal AA requirements for rainbow trout have not been established. This study aimed to elucidate the effects of varying dietary AA levels on survival, growth, long-chain polyunsaturated fatty acid (LC-PUFA) biosynthetic capacity, oxylipin profiles, lipid peroxidation, and stress resistance of rainbow trout fry. Over a period of eight weeks, 4000 female rainbow trout fry at the resorptive stage (0.12 g) from their first feeding were fed diets with varying levels of AA (0.6%, 1.1% or 2.5% of total fatty acids) while survival and growth metrics were closely monitored. The dietary trial was followed by an acute confinement stress test. Notably, while the fatty acid profiles of the fish reflected dietary intake, those fed an AA-0.6% diet showed increased expression of elongase5, highlighting their inherent ability to produce LC-PUFAs from C18 PUFAs and suggesting potential AA or docosapentaenoic acidn-6 (DPAn-6) biosynthesis. However, even with this biosynthetic capacity, the trout fed reduced dietary AA had higher mortality rates. The diet had no effect on final weight (3.38 g on average for the three diets). Conversely, increased dietary AA enhanced eicosanoid production from AA, suggesting potential inflammatory and oxidative consequences. This was further evidenced by an increase in non-enzymatic lipid oxidation metabolites, particularly in the AA-2.5% diet group, which had higher levels of phytoprostanes and isoprostanes, markers of cellular oxidative damage. Importantly, the AA-1.1% diet proved to be particularly beneficial for stress resilience. This was evidenced by higher post-stress turnover rates of serotonin and dopamine, neurotransmitters central to the fish's stress response. In conclusion, a dietary AA intake of 1.1% of total fatty acids appears to promote overall resilience in rainbow trout fry.

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.

Maternal High-Fat Diet Affects the Contents of Eggs and Causes Abnormal Development in the Medaka Fish

Maternal nutritional status can affect development and metabolic phenotypes of progeny in animals. The effects of maternal diet are thought to be mediated mainly by changes inside oocytes such as organelles, maternal RNAs, and metabolites. However, to what extent each factor contributes to offspring phenotypes remains uncertain, especially in viviparous mammalian systems, where factors other than oocytes, such as placenta and milk, need to be considered. Here, using the medaka fish as an oviparous vertebrate model, we examined whether maternal high-fat diet (mHFD) feeding affects offspring development and what kind of changes occur in the contents of mature eggs. We found that mHFD caused the high frequency of embryonic deformities of offspring, accompanied by downregulation of transcription- and translation-related genes and zygotic transcripts at the blastula stage. Transcriptomic and metabolomic analyses of mature eggs suggested decreased catabolism of amino acids and glycogen, moderate upregulation of endoplasmic reticulum stress-related genes, and elevated lipid levels in mHFD eggs. Furthermore, high-fat diet females showed a higher incidence of oocyte atresia and downregulation of egg protein genes in the liver. These data suggest that attenuated amino acid catabolism triggered by decreased yolk protein load/processing, as well as elevated lipid levels inside eggs, are the prime candidates that account for the higher incidence of embryonic deformities in mHFD offspring. Our study presents a comprehensive data on the changes inside eggs in a mHFD model of nonmammalian vertebrates and provides insights into the mechanisms of parental nutritional effects on offspring.

New alternative ingredients and genetic selection are the next game changers in rainbow trout nutrition: a metabolomics appraisal

The formulation of sustainable fish feeds based on plant ingredients supplemented by alternative ingredients to plant (insect, micro-algae, yeast) and genetic selection of fish for plant-based diets were tested on rainbow trout in two separate experiments. Plant-based diets and corresponding diets supplemented with an ingredient mix: insect, micro-algae and yeast in Experiment A, and insect and yeast in Experiment B were compared to commercial-like diets. In experiment A, the mix-supplemented diet was successful in compensating the altered growth performance of fish fed their respective plant-based diet compared to those fed the commercial diet, by restoring feed conversion. In experiment B, the selected line demonstrated improved growth performances of fish fed mix-supplemented and plant-based diets compared to the non-selected line. Metabolomics demonstrated a plasma compositional stability in fish fed mix-supplemented and basal plant-based diets comprising an amino acid accumulation and a glucose depletion, compared to those fed commercial diets. The selected line fed mix-supplemented and commercial diets showed changes in inositol, ethanol and methanol compared to the non-selected line, suggesting an involvement of microbiota. Changes in plasma glycine-betaine content in fish fed the mix-supplemented diet suggest the ability of the selected line to adapt to alternative ingredients.

Effects of a High-Fat Diet on Intestinal and Gonadal Metabolism in Female and Male Sea Cucumber Apostichopus japonicus

Parental nutrient reserves are directly related to reproductive performance in sea cucumbers. This study focused on the lipid requirements of male and female sea cucumbers Apostichopus japonicus during the reproductive stage and analyzed their physiological responses to a high-fat diet (HFD). The intestinal lipid metabolites and microbiome profile changed significantly in animals fed with the HFD, as given by an upregulation of metabolites related to lipid metabolism and an increase in the predominance of Proteobacteria in the microbiome, respectively. The metabolic responses of male and female sea cucumbers to the HFD differed, which in turn could have triggered sex-related differences in the intestinal microbiome. These results suggest that the lipid content in diets can be differentially adjusted for male and female sea cucumbers to improve nutrition and promote reproduction. This data contributes to a better understanding of the reproductive biology and sex differences of sea cucumbers.

Divergent Carry-Over Effects of Hypoxia during the Early Development of Abalone

After being exposed to environmental stimuli during early developmental stages, some organisms may gain or weaken physiological regulating abilities, which would have long-lasting effects on their performance. Environmental hypoxia events can have significant effects on marine organisms, but for breeding programs and other practical applications, it is important to further explore the long-term physiological effects of early hypoxia exposure in economically significant species. In this study, the Pacific abalone Haliotis discus hannai was exposed to moderate hypoxia (∼4 mg/L) from zygote to trochophora, and the assessments of hypoxia tolerance were conducted on the grow-out stage. The results revealed that juvenile abalones exposed to hypoxia at the early development stages were more hypoxia-tolerant but with slower weight growth, a phenomenon called the trade-off between growth and survival. These phenotypic effects driven by the hypoxia exposure were explained by strong selection of genes involved in signal transduction, autophagy, apoptosis, and hormone regulation. Moreover, long non-coding RNA regulation plays an important role modulating carry-over effects by controlling DNA replication and repair, signal transduction, myocardial activity, and hormone regulation. This study revealed that the ability to create favorable phenotypic differentiation through genetic selection and/or epigenetic regulation is important for the survival and development of aquatic animals in the face of rapidly changing environmental conditions.

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.

Molecular programming of the hepatic lipid metabolism via a parental high carbohydrate and low protein diet in rainbow trout

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.

Alteration of eggs biochemical composition and progeny survival by maternal high carbohydrate nutrition in a teleost fish

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.

Black soldier fly full-fat meal in Atlantic salmon nutrition – Part A: Effects on growth performance, feed utilization, selected nutriphysiological traits and production sustainability in fries

Black soldier fly larva meal (BSFM) application as an innovative feed material has been developed in aquaculture nutrition. However, recent scientific literature is still lacking in the case of insect meal effects on different stages of salmonid fish, and the vast majority of research is focused on farmed Atlantic salmon. Therefore, the holistic approach was undertaken in the cycle of two studies carried out: on fries and pre-smolts. This study aimed to evaluate the effect of fish meal (FM) replacement by full-fat BSFM in Atlantic salmon fry diets on the growth performance, feed utilization, crude protein and crude fat digestibility, somatic indices, histomorphology of intestines, and environmental sustainability. Additionally, pellet quality was assessed. Two experiments were performed on 360 Atlantic salmon fries – each of which lasted 60 days. For the first experiment, 240 individuals were distributed to four experimental groups: six replicates (tanks) per group and 10 fish per tank. For the second experiment, 120 individuals were distributed to four experimental groups: three replicates (tanks) per group and 10 fish per tank were used. The following groups were applied: CON – without the addition of full-fat BSFM and with 39% FM; BSFM5 – with 5% addition of full-fat BSFM and 36.1% FM; BSFM10 – with 10% full-fat BSFM and 33.3% FM; BSFM15 – with 15% addition of full-fat BSFM and 30.3% FM. The present study showed satisfactory results of BSFM inclusion at the levels of 5% and 10% as a replacement for fish meal in feeds for Atlantic salmon fries. No negative effects on growth performance, feed utilization, protein and fat digestibility, or intestinal structure were recorded. Simultaneously, insect meal inclusion in Atlantic salmon diets significantly improved the environmental sustainability of the feed. In the case of BSFM15, decreases in body weight gain, protein lipid efficiency ratio, and lipid efficiency ratio, as well as increases in feed conversion ratio, were observed. Therefore, the use of shares higher than 10% of BSFM in Atlantic salmon fries may not be recommended.

Efficacy of Utilization of All-Plant-Based and Commercial Low-Fishmeal Feeds in Two Divergently Selected Strains of Rainbow Trout (Oncorhynchus mykiss): Focus on Growth Performance, Whole-Body Proximate Composition, and Intestinal Microbiome

The present study aimed to investigate the growth performance, whole-body proximate composition, and intestinal microbiome of rainbow trout strains when selected and non-selected for weight gain on all-plant protein diets. A 2x2 factorial design was applied, where a selected (United States) and a non-selected (ITA) rainbow trout strain were fed using either an all-plant protein (PP) or a commercial low-FM diet (C). Diets were fed to five replicates of 20 (PP) or 25 (C) fish for 105 days. At the end of the trial, growth parameters were assessed, and whole fish (15 pools of three fish/diet) and gut samples (six fish/diet) were collected for whole-body proximate composition and gut microbiome analyses, respectively. Independent of the administered diet, the United States strain showed higher survival, final body weight, weight gain, and specific growth rate when compared to the ITA fish (p < 0.001). Furthermore, decreased whole-body ether extract content was identified in the PP-fed United States rainbow trout when compared to the ITA strain fed the same diet (p < 0.001). Gut microbiome analysis revealed the Cetobacterium probiotic-like genus as clearly associated with the United States rainbow trout, along with the up-regulation of the pathway involved in starch and sucrose metabolism. In summary, the overall improvement in growth performance and, to a lesser extent, whole-body proximate composition observed in the selected rainbow trout strain was accompanied by specific, positive modulation of the intestinal microbiome.

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.

Glucose injection into the yolk influences intermediary metabolism in adult Nile tilapia fed with high levels of carbohydrates

Nutritional programming is a concept proposed to be applied in the field of fish nutrition to improve the use of new diets in aquaculture. This study aimed to investigate for the first time the effects of a glucose injection into the yolk at the alevin stage on intermediary metabolism and growth in adult Nile tilapia (Oreochromis niloticus) at 32-37 weeks later in the life. The early stimulus was performed through direct microinjection of 2 M glucose into yolk sacs of Nile tilapia alevin. Subsequently, in adult tilapia, the long-term effects of glucose stimulus on growth performance, blood metabolites, chemical composition in the liver and muscle, expression of genes involved in glucose transport and metabolism (glycolysis and gluconeogenesis) and related pathways (amino acid catabolism and lipogenesis) were investigated. Our results showed that, even though early glucose injection had no effect on growth performance in adult fish, very few significant effects on glucose metabolism were observed. Furthermore, to evaluate the potential metabolic programming after a dietary challenge, a 2 × 2 factorial design with two early stimuli (0.85% NaCl or 2 M glucose) and two different dietary carbohydrate intakes (medium-carbohydrate diet, CHO-M; high-carbohydrate diet, CHO-H) was performed between weeks 33 and 37. As expected, compared with the CHO-M diet, the CHO-H diet led to decreased growth performance, higher glyceamia and triglyceridemia, higher glycogen and lipid levels in the liver as well as down-regulation of gluconeogenesis and amino acid catabolism gene expressions. More interestingly, although early glucose injection had no significant effect on growth performance, it enhanced the capacities for lipogenesis, glycolysis and gluconeogenesis, particularly in fish that were fed the CHO-H diet. Thus, the nutritional programming of tilapia linked to glucose injection into the yolk of alevins is always visible at the adult stage albeit less intense than what we previously observed in juvenile.

Modulation of Energy Metabolism and Epigenetic Landscape in Rainbow Trout Fry by a Parental Low Protein/High Carbohydrate Diet

Simple Summary

While the effects of parental diets on their progeny have been highly described in mammals, such studies are lacking in fish. To explore such a question in a high trophic level teleost fish, two-year old male and female rainbow trout were fed either a control diet (0% carbohydrate and 63.89% protein) or a high-carbohydrate diet (35% carbohydrate and 42.96% protein), for a complete reproductive cycle for females and for a period of 5 months for males. Neither the maternal nor the paternal high-carbohydrate diet alone had induced significant effects on their progeny. Nevertheless, when both parents were fed the high-carbohydrate diet, the energy metabolism and mitochondrial dynamics of their progeny were altered. Moreover, the epigenetic landscape was also highly affected. Even though, offspring growth was only slightly affected at the early stage of life; the effect of parental high-carbohydrate diet should be explored over the long term.

Abstract

It is now recognized that parental diets could highly affect offspring metabolism and growth. Studies in fish are, however, lacking. In particular, the effect of a parental diet high in carbohydrate (HC) and low in protein (LP) on progeny has never been examined in higher trophic level teleost fish. Thus, two-year old male and female rainbow trout (Oncorhynchus mykiss) were fed either a control diet (0% carbohydrate and 63.89% protein) or a diet containing 35% carbohydrate and 42.96% protein (HC/LP) for a complete reproductive cycle for females and over a 5-month period for males. Cross-fertilizations were then carried out. To evaluate the effect of the parental diet on their offspring, different phenotypic and metabolic traits were recorded for offspring before their first feeding and again three weeks later. When considering the paternal and maternal HC/LP nutrition independently, fry phenotypes and transcriptomes were only slightly affected. The combination of the maternal and paternal HC/LP diets altered the energy metabolism and mitochondrial dynamics of their progeny, demonstrating the existence of a synergistic effect. The global DNA methylation of whole fry was also highly affected by the HC/LP parental diet, indicating that it could be one of the fundamental mechanisms responsible for the effects of nutritional programming.

Putative imbalanced amino acid metabolism in rainbow trout long term fed a plant-based diet as revealed by 1H-NMR metabolomics

The long-term effect of a plant (P)-based diet was assessed by proton nuclear magnetic resonance (¹H-NMR) metabolomics in rainbow trout fed a marine fish meal (FM)-fish oil (FO) diet (M), a P-based diet and a control commercial-like diet (C) starting with the first feeding. Growth performances were not heavily altered by long-term feeding on the P-based diet. An ¹H-NMR metabolomic analysis of the feed revealed significantly different soluble chemical compound profiles between the diets. A set of soluble chemical compounds was found to be specific either to the P-based diet or to the M diet. Pterin, a biomarker of plant feedstuffs, was identified both in the P-based diet and in the plasma of fish fed the P-based diet. ¹H-NMR metabolomic analysis on fish plasma and liver and muscle tissues at 6 and 48 h post feeding revealed significantly different profiles between the P-based diet and the M diet, while the C diet showed intermediate results. A higher amino acid content was found in the plasma of fish fed the P-based diet compared with the M diet after 48 h, suggesting either a delayed delivery of the amino acids or a lower amino acid utilisation in the P-based diet. This was associated with an accumulation of essential amino acids and the depletion of glutamine in the muscle, together with an accumulation of choline in the liver. Combined with an anticipated absorption of methionine and lysine supplemented in free form, the present results suggest an imbalanced essential amino acid supply for protein metabolism in the muscle and for specific functions of the liver.

Influence of Parental Fatty Acid Desaturase 2 (fads2) Expression and Diet on Gilthead Seabream (Sparus aurata) Offspring fads2 Expression during Ontogenesis

Simple Summary

The present study was on the gene expression of a rate-limiting enzyme in long chain polyunsaturated fatty acids (LC-PUFAs), fatty acyl desaturase 2 (fads2), throughout the embryonic development of a gilthead sea bream. The results showed a maternal transfer of fads2 mRNA to the developing oocyte. The embryonic fads2 expression might start after the neurula stage. No effect was found in fads2 expression in developing eggs from broodstock fed with a diet rich in rapeseed oil or fish oil. The present study provides information on the change of LC-PUFA biosynthesis during embryogenesis.

Abstract

Previous studies have shown that it is possible to increase the ability of marine fish to produce long-chain polyunsaturated fatty acid from their 18C precursors by nutritional programming or using broodstock with a higher fatty acyl desaturase 2 (fads2) expression. However, those studies failed to show the effect of these interventions on the expression of the fads2 gene in the developing egg. Moreover, there were no studies on the temporal expression of the fads2 during ontogeny in the gilthead sea bream (Sparus aurata). In order to determine the changes in expression of fads2 during ontogeny, gilthead sea bream broodstock with a high (HRO) or low (LRO) fads2 expression fed a diet previously used for nutritional programming, or a fish oil-based diet (LFO) were allowed to spawn. The samples were taken at the stages of spawning, morula, high blastula, gastrula, neurula, heart beating, hatch and 3 day-old first exogenous feeding larvae to determine fads2 expression throughout embryonic development. The results showed the presence of fads2 mRNA in the just spawned egg, denoting the maternal mRNA transfer to the developing oocyte. Later, fads2 expression increased after the neurula, from heart beating until 3-day-old larvae, denoting the transition from maternal to embryonic gene expression. In addition, the eggs obtained from broodstock with high fads2 expression showed a high docosahexaenoic acid content, which correlated with the downregulation of the fads2 expression found in the developing embryo and larvae. Finally, feeding with the nutritional programming diet with the partial replacement of fish oil by rapeseed oil did not affect the long chain polyunsaturated fatty acid (LC-PUFA) contents nor fads2 expression in the gilthead sea bream developing eggs.

Black Soldier Fly Full-Fat Larvae Meal as an Alternative to Fish Meal and Fish Oil in Siberian Sturgeon Nutrition: The Effects on Physical Properties of the Feed, Animal Growth Performance, and Feed Acceptance and Utilization

Simple Summary

Research for alternative protein sources that may replace fish meal and fish oil in fish diets is one of the ongoing tasks for aquaculture. Sturgeons role captive fish production increases due to the rapid decrease in its wild stocks during the 20th century. Insect meals are a novel group of feed materials rich in nutrients that are produced in an environmentally sustainable way. Therefore, the aim of the study was to assess the effects of black soldier fly larvae full-fat meal (BSFL) usage as fish meal and fish oil replacement in Siberian sturgeon diets. The experimentally obtained data showed the possibility of extruded feed production with up to 30% of BSFL and physical parameters suitable for fish feeding. Moreover, feed acceptance increase was observed in treatments containing than 10% and higher shares of BSFL. In the groups whose feed contained 5 to 30% of BSFL in the diet, the growth of experimental fish as well as their feed utilization parameters were improved; however, with no effects on feed digestibility. All presented data make BSFL a suitable nutrient source alternative to fish meal in Siberian sturgeon nutrition.

Abstract

This study provides data on the use of black soldier fly (Hermetia illucens) full-fat meal (BSFL) in Siberian sturgeon (Acipenser baerii) nutrition, examining pellet physical properties, growth performance, feed acceptance and utilization, apparent protein, and fat digestibility. The study consisted of: feed quality assessment; a growth performance; feed acceptance; digestibility trials. The effect of the use of BSFL as a replacement for fish meal (FM) and fish oil (FO) was investigated. The applied BSFL shares were 5%, 10%, 15%, 20%, 25%, and 30% of the diet, replacing up to 61.3% of FM and allowing us to reduce FO use by up to 95.4% in the case of 30% incorporation. The applied substitution affected feed quality, increasing the expansion rate, and decreasing feed density, sinking speed and water stability. However, body weight gain, specific growth rate, feed, and protein conversion ratios, were improved in groups fed BSFL. Moreover, feed acceptance was increased with treatments containing 10 to 30% BSFL. No effects on nutrients digestibility were observed. The results show that the use of BSFL as an FM and FO replacement may have positive effects on sturgeon growth performance, and BSFL can be developed as a promising alternative feed material.

Impact on cerebral function in rainbow trout fed with plant based omega-3 long chain polyunsaturated fatty acids enriched with DHA and EPA

Characterization and modulation of cerebral function by ω-3 long chain polyunsaturated fatty acids (ω-3 LC-PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) enrichment in plant based-diet were studied in rainbow trout (Oncorhynchus mikyss). We hypothesized that ω-3 LC-PUFAs are involved in the regulation of cerebral function in fish. During nine weeks, we examined the growth performance of rainbow trout for three experimental plant based-diets containing distinct levels of EPA and DHA. Using RT-qPCR, we assessed mRNA genes related to feeding behavior regulated by the central nervous system of humans, rodents and fish. These include markers of neuropeptides, indicators of cellular specification, animal stress, oxidant status, cytokines and genes regulating animal behaviour. ω-3 LC-PUFAs enrichment decreased daily food intake and induced a simultaneous mRNA expression increase in orexigenic transcript npy peptide and a decrease in anorexigen transcript pomcA peptide in the hypothalamus. Overall transcript genes related to proinflammatory cytokines, inflammation, antioxidant status, cortisol pathway, serotoninergic pathways and dopaminergic pathways were down-regulated in the juveniles fed the high ω-3 LC-PUFAs diet. However, the mRNA expression of transcripts related to cell specification were down regulated, namely tmem119 markers of microglial cell in forebrain and midbrain, gfap markers of astrocyte in the midbrain, and rbfox3 markers of neurons in the midbrain and hindbrain in juveniles fed high ω-3 experimental diet. In conclusion, this study revealed that a diet rich in ω-3 LC-PUFAs affected a relatively high proportion of the brain function in juvenile rainbow trout through mechanisms comparable to those characterized previously in mammals.

Effects of different dietary oils on egg quality and reproductive performance in rainbow trout Oncorhynchus mykiss

The study was conducted to evaluate effects of different dietary oils on egg quality and reproductive performance in rainbow trout. Broodfish (≈ 870 g) were fed four iso-nitrogenous and iso-lipidic diets differing in lipid sources: fish oil (FO), linseed oil (LO) and sesame oil (SO) as well as a commercial trout diet (CD) for about 5 months prior to spawning. Growth performance did not differ among the trout in the treatment groups. Mean diameter, volume and weight of eggs did not differ among the dietary treatments. Absolute fecundity, relative fecundity and gonadosomatic index were not affected by dietary treatment. A sub-set of eggs from females fed the experimental diets were fertilized to assess the reproductive performance of broodfish. When diets were fed, devoid of fish oil, fertilization rates were 89.2 ± 5.8 and 92.1 ± 4.9 %, eyeing rates were 87.3 ± 5.3 and 84.1 ± 4.4 % and hatching rates were 81.2 ± 4.3 and 78.3 ± 3.4 % in LO and SO fed fish, respectively. Fatty acid content of the eggs from broodstocks with a different nutritional history was affected by the dietary lipid sources. Eicosapentaenoic acid (EPA), arachidonic acid (ARA), and docosahexaenoic acid (DHA) concentrations in females fed vegetable oil based diets were greater than the dietary concentrations. Overall, results from the present study indicate there can be inclusion of LO or SO as dietary lipid sources without compromising egg quality and reproductive performance. Furthermore, there is efficient bioconversion of 18C fatty acids to 20-22 C fatty acids in rainbow trout.

Characterization and modulation of brain lipids content of rainbow trout fed with 100% plant based diet rich in omega-3 long chain polyunsaturated fatty acids DHA and EPA

Brain functions are known to be mainly modulated by adequate dietary intake. Inadequate intake as can be an excess or significant deficiency affect cognitive processes, behavior, neuroendocrine functions and synaptic plasticity with protective or harmful effects on neuronal physiology. Lipids, in particular, ω-6 and ω-3 long chain polyunsaturated fatty acids (LC-PUFAs) play structural roles and govern the different functions of the brain. Hence, the goal of this study was to characterize the whole brain fatty acid composition (precursors, enzymatic and non-enzymatic oxidation metabolites) of fish model of rainbow trout fed with three experimental plant-based diet containing distinct levels of eicosapentaenoic acid (EPA, 20:5 ω-3) and docosahexaenoic acid (DHA, 22:6 ω-3) (0% for low, 15.7% for medium and 33.4% for high, total fatty acid content) during nine weeks. Trout fed with the diet devoid of DHA and EPA showed reduced brain content of total ω-3 LC-PUFAs, with diminution of EPA and DHA. Selected enzymatic (cyclooxygenases and lipoxygenases) oxidation metabolites of arachidonic acid (AA, 20:4 ω-6) decrease in medium and high ω-3 LC-PUFAs diets. On the contrary, total selected enzymatic oxidation metabolites of DHA and EPA increased in high ω-3 LC-PUFAs diet. Total selected non-enzymatic oxidation metabolites of DHA (not detected for EPA) increased in medium and high ω-3 LC-PUFAs diets. In conclusion, this work revealed for the first time in fish model the presence of some selected enzymatic and non-enzymatic oxidation metabolites in brain and the modulation of brain lipid content by dietary DHA and EPA levels.

Transgenerational disrupting impacts of atrazine in zebrafish: Beneficial effects of dietary spirulina

In a range of fish species, offspring sustainability is much dependent to their mother's investment into the egg yolk. A healthy environment helps broodfish to produce normal quality offspring. However, deviation from optimal conditions can disturb body functions that effect the next generation. Here, zebrafish (Danio rerio) was employed to investigate the transgenerational impacts of an immunotoxic and endocrine disruptor, atrazine (AZ). In addition, the possible ameliorated effects of a nutraceutical, Arthrospira platensis (spirulina- SP), was considered. Adult females were either exposed to 0 (Cn), 5 (AZ5), and 50 (AZ50) μg/L AZ or fed SP-supplemented diet (10 g/kg; SP). In combination treatments, fish were also exposed to AZ and fed SP (SP-AZ5 and SP-AZ50). Embryos were obtained after 28 d of exposure. Exposure to AZ50 caused females to produce eggs with significantly lower fertilization and hatching. No changes were observed in the concentrations of thyroid hormones. AZ significantly increased cortisol response and reduced levels of immunoglobulin, lysozyme and complement activities in females and their offspring. SP-AZ5 and SP-AZ50 females, however, resisted to the toxic effects of AZ, produced embryos with lower cortisol content and higher immunity competence. Bactericidal activity of the embryos also showed the transgenerational antimicrobial effects of SP along with the AZ immunotoxicity. Overall, these results indicate that AZ could have long lasting toxic effects on fish, and that dietary SP-supplementation could ameliorate AZ induced transgenerational toxic effects.

Replacing Dietary Fish Oil with Vegetable Oil Blends in Female Rainbow Trout Brood Stock Does Not Affect Breeding Quality

To determine the effects of replacing fish oil (FO) with a mixture of vegetable oils (VO) in plant protein-rich diets on reproductive performance, the fatty acid profile of embryos as well as health indices of female rainbow trout (Oncorhynchus mykiss) brooders (initial mean body weight, 1.8 ± 0.1 kg), a 3-month feeding trial was conducted. Four isoproteic (ca. 42%) and isoenergetic (ca. 20 MJ/kg) diets were formulated in which 50% (FO50/VO50), 75% (FO25/VO75), and 100% (VO100) of FO were replaced by a mixture of VO, whereas the control diet (FO100) was prepared with FO as the major source of lipid. Fish fed the VO100 had the lowest fertilization (73.0 ± 2.5%), survival at eyed-embryo stage (62.5 ± 5.0%), and hatching rate (56.0 ± 4.7%) rates. Brood fish fed the FO50/VO50, FO25/VO50, and VO100 diets had higher levels of saturated and monounsaturated fatty acids in embryos in comparison with fish fed FO100 diet. The levels of docosahexaenoic acid of embryos gradually decreased during embryogenesis in all treatments, whereas the concentrations of eicosapentaenoic acid was greatly increased at hatching day (35 days after spawning). Regarding serum biochemical parameters, fish fed the VO100 diet had the highest serum glucose, cholesterol, and low-density lipoprotein levels. The results of the current study revealed that replacement of dietary FO with a mixture of VO up to 75% did not have any adverse effects on reproductive performance and health indices of O. mykiss females.

Endogenous production of n-3 long-chain PUFA from first feeding and the influence of dietary linoleic acid and the α-linolenic:linoleic ratio in Atlantic salmon (Salmo salar)

Atlantic salmon (Salmo salar) possess enzymes required for the endogenous biosynthesis of n-3 long-chain PUFA (LC-PUFA), EPA and DHA, from α-linolenic acid (ALA). Linoleic acid (LA) competes with ALA for LC-PUFA biosynthesis enzymes leading to the production of n-6 LC-PUFA, including arachidonic acid (ARA). We aimed to quantify the endogenous production of EPA and DHA from ALA in salmon fed from first feeding on diets that contain no EPA and DHA and to determine the influence of dietary LA and ALA:LA ratio on LC-PUFA production. Salmon were fed from first feeding for 22 weeks with three diets formulated with linseed and sunflower oils to provide ALA:LA ratios of approximately 3:1, 1:1 and 1:3. Endogenous production of n-3 LC-PUFA was 5·9, 4·4 and 2·8 mg per g fish and that of n-6 LC-PUFA was 0·2, 0·5 and 1·4 mg per g fish in salmon fed diets with ALA:LA ratios of 3:1, 1:1 and 1:3, respectively. The ratio of n-3:n-6 LC-PUFA production decreased from 27·4 to 2·0, and DHA:EPA ratio increased and EPA:ARA and DHA:ARA ratios decreased, as dietary ALA:LA ratio decreased. In conclusion, with a dietary ALA:LA ratio of 1, salmon fry/parr produced about 28 μg n-3 LC-PUFA per g fish per d, with a DHA:EPA ratio of 3·4. Production of n-3 LC-PUFA exceeded that of n-6 LC-PUFA by almost 9-fold. Reducing the dietary ALA:LA ratio reduced n-3 LC-PUFA production and EPA:ARA and DHA:ARA ratios but increased n-6 LC-PUFA production and DHA:EPA ratio.

The Utilization of Full-Fat Insect Meal in Rainbow Trout (Oncorhynchus mykiss) Nutrition: The Effects on Growth Performance, Intestinal Microbiota and Gastrointestinal Tract Histomorphology

A 71-day-long experiment was conducted to evaluate the inclusion of 20% Hermetia illucens (HI) meal; Tenebrio molitor (TM) meal; Gryllodes sigillatus (GS) meal; and Blatta lateralis (BL) meal in comparison to a control diet without any insect-based materials that used fish meal as the main source of protein. A total of 1950 rainbow trout juveniles (53.39 ± 3.74 g) were used. The formulated diets were isonitrogenous (45%) and isoenergetic (10 MJ kg−1). The inclusion of a full-fat insect meal did not affect the survival rate during the experimental period. The growth performance was significantly improved in the BL and TM treatments, while in the HI treatment was not affected. However, the GS treatment had a negative effect on the growth performance. The villus height decreased in the TM and GS treatment groups and increased in the BL diet group. The total number of bacteria increased in all insect meal diet groups. The results of the experiment show that B. lateralis, T. molitor and H. illucens full-fat meals can be used as a partial fish meal replacement without negative effects on survival or growth performance parameters. Moreover, full-fat insect meals may be considered as a protein source and a functional feed component that may positively affect the histomorphological structure of the fish gastrointestinal tract and stimulate the expansion of beneficial bacterial populations in the gut.

Utilization of marine fisheries wastes for the production of the freshwater fish Cyprinus carpio

The present study was aimed to assess the effects of complete replacement of fish meal with fisheries waste meals on survival, growth performance, digestive enzyme activities, and muscle compositions of the freshwater fish Cyprinus carpio. The proximate composition and mineral contents of three different fisheries wastes, such as Rastrelliger kanagurta, Sphyraena barracuda, and Fenneropenaeus indicus were analyzed. Based on the nutrient content of these fisheries waste, one control fish meal diet and three different complete fish meal replacement diets (diet 1, diet 2, and diet 3 formulated with R. kanagurta, S. barracuda, and F. indicus waste meals, respectively) were formulated. Fingerlings C. carpio were fed with these diets for a period of 6 weeks. Results from feeding experiments showed insignificant (p > 0.05) differences in survival, growth, and feed intake of C. carpio fed with control and three different fisheries waste diets. However, the digestive enzyme activity and muscle biochemical compositions were significantly (p < 0.05) altered in F. indicus waste meal fed C. carpio compared to other fisheries waste meal and control diets fed fish groups. Therefore, the present study suggests that R. kanagurta, S. barracuda, and F. indicus waste meals can be considered as alternative feed ingredients for fish meal to formulate low-cost feeds for C. carpio culture.

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.

Effects of resveratrol and genistein on growth, nutrient utilization and fatty acid composition of rainbow trout

The replacement of the finite and costly resource fish oil is an important task for aquaculture nutrition. A promising approach could be the use of plant bioactives that may have the potential to influence the metabolism and the synthesis of n-3 long chain polyunsaturated fatty acids, especially EPA (20:5n-3) and DHA (22:6n-3). In this study, the two phytochemicals resveratrol (RV) and genistein (G) were investigated for their effects on fish growth, nutrient utilization and body nutrient composition alongside their effects on whole body fatty acid (FA) composition. In a feeding trial lasting 8 weeks, rainbow trout (initial BW: 81.4±0.5 g) were held in a recirculating aquaculture system and fed six experimental diets with varying fish oil levels as plain variants or supplemented with 0.3% of dry matter (DM) of either RV or G. The six diets were as follows: diet F4 had 4% DM fish oil, diet F0 had 0% DM fish oil, diets F4+RV, F4+G, F0+RV and F0+G were equal to the diets F4 and F0, respectively, and supplemented with the phytochemicals RV and G. The feeding of the F0+RV diet resulted in reduced feed intake, growth rate and slightly reduced whole body lipid levels. At the same time, the amount of polyunsaturated FA and the n-3/n-6 ratio were significantly increased in whole body homogenates of rainbow trout fed diet F0+RV in comparison to the F0 control. The feeding of the F0+G diet led to reduced feed intake, slightly increased protein utilization but did not significantly affect the whole body FA composition. Overall, feeding the fish oil-free diet supplemented with the phytochemicals resulted in more pronounced effects on fish performance and FA composition than the single factors per se (dietary fish oil level or phytochemical). Present data indicate that G might not be of profitable use for trout nutrition. In terms of FA composition, RV could be a potentially useful complement for fish oil. However, the impairment of growth and performance parameters as observed in the present study discourages its use in trout diets.

Epigenetics in teleost fish: From molecular mechanisms to physiological phenotypes

While the field of epigenetics is increasingly recognized to contribute to the emergence of phenotypes in mammalian research models across different developmental and generational timescales, the comparative biology of epigenetics in the large and physiologically diverse vertebrate infraclass of teleost fish remains comparatively understudied. The cypriniform zebrafish and the salmoniform rainbow trout and Atlantic salmon represent two especially important teleost orders, because they offer the unique possibility to comparatively investigate the role of epigenetic regulation in 3R and 4R duplicated genomes. In addition to their sequenced genomes, these teleost species are well-characterized model species for development and physiology, and therefore allow for an investigation of the role of epigenetic modifications in the emergence of physiological phenotypes during an organism's lifespan and in subsequent generations. This review aims firstly to describe the evolution of the repertoire of genes involved in key molecular epigenetic pathways including histone modifications, DNA methylation and microRNAs in zebrafish, rainbow trout, and Atlantic salmon, and secondly, to discuss recent advances in research highlighting a role for molecular epigenetics in shaping physiological phenotypes in these and other teleost models. Finally, by discussing themes and current limitations of the emerging field of teleost epigenetics from both theoretical and technical points of view, we will highlight future research needs and discuss how epigenetics will not only help address basic research questions in comparative teleost physiology, but also inform translational research including aquaculture, aquatic toxicology, and human disease.

Long-term dietary replacement of fishmeal and fish oil in diets for rainbow trout (Oncorhynchus mykiss): Effects on growth, whole body fatty acids and intestinal and hepatic gene expression

The effects of replacing fishmeal and fish oil with a plant-based diet were studied in juvenile (10g) and ongrowing (250-350g) rainbow trout from first-feeding. Feed-related differences in the intestinal and hepatic transcriptome were examined in juveniles after 7 months of feeding at 7°C. Based on microarray results obtained for juveniles, the expression of selected genes related to lipid, cholesterol and energy metabolisms, was assessed by RT-qPCR in ongrowing trout after 6 additional months of feeding at 17°C. Plasma glucose and cholesterol, lipid content and fatty acid profile of whole body were analyzed at both stages. After 7 months at 7°C, all juveniles reached the same body weight (10g), while at 13 months ongrowing fish fed the totally plant-based diet exhibited lower body weight (234 vs 330-337g). Body lipid content was higher in juveniles fed the totally plant-based diet (13.2 vs 9.4–9.9%), and plasma cholesterol was about 2-times lower in trout fed the plant-based diets at both stages. Fatty acid profile mirrored that of the respective diet, with low proportions of long-chain n-3 polyunsaturated fatty acids in fish fed plant-based diets. Genes involved in protein catabolism, carbohydrate metabolism and trafficking were down-regulated in the intestines of juveniles fed the plant-based diets. This was not true for ongrowing fish. Genes involved in lipid and cholesterol metabolisms were up-regulated in the livers of fish fed plant-based diets for both stages. In this study, feeding trout a totally plant-based diet from first-feeding affect a relatively low proportion of metabolism-related genes. In the longer term, when fish were reared at a higher temperature, only some of these changes were maintained (i.e. up-regulation of lipid/cholesterol metabolism). Although the plant-based diets tested in this study had no major deficiencies, small adjustments in the feed-formula are needed to further optimize growth performance while sparing marine resources.

Successful selection of rainbow trout (Oncorhynchus mykiss) on their ability to grow with a diet completely devoid of fishmeal and fish oil, and correlated changes in nutritional traits

In the context of limited marine resources, the exponential growth of aquaculture requires the substitution of fish oil and fishmeal, the traditional components of fish feeds by terrestrial plant ingredients. High levels of such substitution are known to negatively impact fish performance such as growth and survival in rainbow trout (Oncorhynchus mykiss) as in other salmonids. In this respect, genetic selection is a key enabler for improving those performances and hence for the further sustainable development of aquaculture. We selected a rainbow trout line over three generations for its ability to survive and grow on a 100% plant-based diet devoid of both fish oil and fishmeal (V diet) from the very first meal. In the present study, we compared the control line and the selected line after 3 generations of selection, both fed either the V diet or a marine resources-based diet (M diet). The objective of the study was to assess the efficiency of selection and the consequences on various correlated nutritional traits: feed intake, feed efficiency, digestibility, composition of whole fish, nutrient retention and fatty acid (FA) profile. We demonstrated that the genetic variability present in our rainbow trout population can be selected to improve survival and growth. The major result of the study is that after only three generations of selection, selected fish fed the V diet grew at the same rate as the control line fed the M diet, whilst the relative reduction of body weight was 36.8% before the selection. This enhanced performance on the V diet seems to be mostly linked to a higher feed intake for the selected fish.

Regulation of genes related to cholesterol metabolism in rainbow trout (Oncorhynchus mykiss) fed a plant-based diet

When compared with fish meal and fish oil, plant ingredients differ not only in their protein content and amino acid and fatty acid profiles but are also devoid of cholesterol, the major component of cell membrane and precursor of several bioactive compounds. Based on these nutritional characteristics, plant-based diets can affect fish physiology and cholesterol metabolism. To investigate the mechanisms underlying cholesterol homeostasis, rainbow trout were fed from 1 g body wt for 6 mo with a totally plant-based diet (V), a marine diet (M), and a marine-restricted diet (MR), with feed intake adjusted to that of the V group. The expression of genes involved in cholesterol synthesis, esterification, excretion, bile acid synthesis, and cholesterol efflux was measured in liver. Results showed that genes involved in cholesterol synthesis were upregulated in trout fed the V diet, whereas expression of genes related to bile acid synthesis ( cyp7a1) and cholesterol elimination ( abcg8) were reduced. Feeding trout the V diet also enhanced the expression of srebp-2 while reducing that of lxrα and miR-223. Overall, these data suggested that rainbow trout coped with the altered nutritional characteristics and absence of dietary cholesterol supply by increasing cholesterol synthesis and limiting cholesterol efflux through molecular mechanisms involving at least srebp-2, lxrα, and miR-223. However, plasma and body cholesterol levels in trout fed the V diet were lower than in fish fed the M diet, raising the question of the role of cholesterol in the negative effect of plant-based diet on growth.

Fatty Acid Profile Is Modulated by Dietary Resveratrol in Rainbow Trout (Oncorhynchus mykiss)

To produce fish of a high quality that are rich in omega-3 fatty acids (n-3 FA) and simultaneously generate more sustainable aquaculture, the combined use of phytochemicals and vegetable oils in fish feed seems to be a promising approach. Resveratrol (RV) potentially induces endogenous fatty acid synthesis, resulting in elevated n-3 FA levels in fish. RV putatively influences ∆6-desaturase, the key enzyme in FA metabolism, and serves as a ligand for PPARα, a transcription factor regulating β-oxidation. Rainbow trout (36.35 ± 0.03 g) were randomly allocated into six groups and fed diets with reduced fish oil levels (F4 = 4%, F2 = 2% and F0 = 0% of dry matter) supplemented with 0.3% (w/w) RV (F4 + RV, F2 + RV and F0 + RV). RV significantly affected FA composition in liver tissue and whole fish homogenates. 20:5n-3 (EPA) and 22:6n-3 (DHA) were significantly increased whereas precursor FA were diminished in fish fed the F2 + RV and F0 + RV diets when compared to F4 + RV and F0. RV significantly elevated ∆6-desaturase protein levels in the livers of F0 + RV fed animals. Hepatic mRNA expression of ∆6-desaturase, PPARα, and its target genes were affected by the dietary fish oil level and not by dietary RV. The results of this study indicated a potential benefit of supplementing RV in fish oil deprived diets elevating n-3 FA levels in rainbow trout.

Long-term programming effect of embryonic hypoxia exposure and high-carbohydrate diet at first feeding on glucose metabolism in juvenile rainbow trout

Environmental conditions experienced during early life play an important role in the long-term metabolic status of individuals. The present study investigated whether hypoxia exposure [for 24 h: 2.5 mg O₂ l^-1 (20% dissolved O₂)] during the embryonic stage alone (hypoxic history) or combined with a 5-day high-carbohydrate (60%) diet stimulus at first feeding (HC dietary history) can affect glucose metabolism later in life, i.e. in juvenile fish. After 19 weeks of growth, we observed a decrease in final body mass in fish with an HC dietary history. Feed efficiency was significantly affected by both hypoxic and HC dietary histories. After a short challenge test (5 days) performed with a 30% carbohydrate diet in juvenile trout, our results also showed that, in trout that experienced hypoxic history, mRNA levels of gluconeogenic genes in liver and glucose transport genes in both liver and muscle were significantly increased at the juvenile stage. Besides, mRNA levels of glycolytic genes were decreased in fish with an HC dietary history. Both hypoxic and dietary histories barely affected plasma metabolites or global epigenetic modifications in juvenile fish after the challenge test. In conclusion, our results demonstrated that an acute hypoxic stimulus during early development alone or combined with a hyperglucidic stimulus at first feeding can modify growth performance and glucose metabolism at the molecular level in juvenile trout.

Exposure to an acute hypoxic stimulus during early life affects the expression of glucose metabolism-related genes at first-feeding in trout

Rainbow trout (Oncorhynchus mykiss) is considered a "glucose-intolerant" species. With the aim of programming trout to improve their metabolic use of dietary carbohydrates, we hypothesised that a hypoxic stimulus applied during embryogenesis could later affect glucose metabolism at the first-feeding stage. An acute hypoxic stimulus (2.5 or 5.0 mg·L-1 O2) was applied for 24 h to non-hatched embryos or early hatched alevins followed by a challenge test with a high carbohydrate diet at first-feeding. The effectiveness of the early hypoxic stimulus was confirmed by the induction of oxygen-sensitive markers such as egln3. At first-feeding, trout previously subjected to the 2.5 mg·L-1 O2 hypoxia displayed a strong induction of glycolytic and glucose transport genes, whereas these glucose metabolism-related genes were affected much less in trout subjected to the less severe (5.0 mg·L-1 O2) hypoxia. Our results demonstrate that an acute hypoxic stimulus during early development can affect glucose metabolism in trout at first-feeding.

Combination of chlorogenic acid and salvianolic acid B protects against polychlorinated biphenyls-induced oxidative stress through Nrf2

Caffeic acid derivatives (CADs) are well-known phytochemicals with multiple physiological and pharmacological activities. This study aimed to investigate the combined protective effects of CADs on PCB126-induced liver damages and oxidative stress in mice. Here, we used chemiluminescence and chose chlorogenic acid (CGA), salvianolic acid B (Sal B) as the best antioxidants. Then, mice were intragastrically administered with 60mg/kg/d CGA, Sal B, and CGA plus Sal B (1:1) for 3 weeks before exposing to 0.05mg/kg/d PCB126 for 2 weeks. We found that pretreatment with CGA, Sal B, and CGA plus Sal B effectively attenuated liver injury and cytotoxicity caused by PCB126, but improved the expressions of superoxide dismutase (SOD), glutathione reduced (GSH), heme oxygenase-1 (HO-1) and nuclear factor E2-related factor 2 (Nrf2), CGA plus Sal B especially, was found to have the best effects that indicated a synergetic protective effect. Taken together, as the Nrf2 regulates the cyto-protective response by up-regulating the expression of antioxidant genes, we suggested that CGA plus Sal B had a combined protection on PCB126-induced tissue damages and that the Nrf2 signaling might be involved.

Environmental health impacts of feeding crops to farmed fish

Half of the seafood consumed globally now comes from aquaculture, or farmed seafood. Aquaculture therefore plays an increasingly important role in the global food system, the environment, and human health. Traditionally, aquaculture feed has contained high levels of wild fish, which is unsustainable for ocean ecosystems as demand grows. The aquaculture industry is shifting to crop-based feed ingredients, such as soy, to replace wild fish as a feed source and allow for continued industry growth. This shift fundamentally links seafood production to terrestrial agriculture, and multidisciplinary research is needed to understand the ecological and environmental health implications. We provide basic estimates of the agricultural resource use associated with producing the top five crops used in commercial aquaculture feed. Aquaculture's environmental footprint may now include nutrient and pesticide runoff from industrial crop production, and depending on where and how feed crops are produced, could be indirectly linked to associated negative health outcomes. We summarize key environmental health research on health effects associated with exposure to air, water, and soil contaminated by industrial crop production. Our review also finds that changes in the nutritional content of farmed seafood products due to altered feed composition could impact human nutrition. Based on our literature reviews and estimates of resource use, we present a conceptual framework describing the potential links between increasing use of crop-based ingredients in aquaculture and human health. Additional data and geographic sourcing information for crop-based ingredients are needed to fully assess the environmental health implications of this trend. This is especially critical in the context of a food system that is using both aquatic and terrestrial resources at unsustainable rates.

Does broodstock nutritional history affect the response of progeny to different first-feeding diets? A whole-body transcriptomic study of rainbow trout alevins

The whole-body transcriptome of trout alevins was characterised to investigate the effects of long-term feeding of rainbow trout broodstock females a diet free of fishmeal and fish oil on the metabolic capacities of progeny. Effects were studied before first feeding and after 3 weeks of feeding diets containing different proportions of marine and plant ingredients. Feeding alevins plant-based diets resulted in lower fish body weight, irrespective of maternal nutritional history. No differences in whole-body lipids were found between treatments, and the tissue fatty acid profile strongly reflected that of the respective broodstock or first-feeding diets. We showed that the maternal diet history did not significantly affect expressions of any genes before the first feeding. Interestingly, we found an effect of maternal nutritional history on gene expression in alevins after 3 weeks of feeding. The major differences in the transcriptome of alevins from plant-based diet-fed females compared with those from commercial-fed females were as follows: (i) down-regulation of genes involved in muscle growth/contraction and (ii) up-regulation of genes involved in carbohydrate and energy metabolism related to the delay in growth/development observed with plant-based diets. Our findings also showed an effect of the first-feeding diets, irrespective of maternal nutritional history. Specifically, the introduction of plant ingredients resulted in the up-regulation of genes involved in amino acid/protein and cholesterol metabolism and in differences in the expressions of genes related to carbohydrate metabolism. Information gained through this study opens up avenues for further reduction of marine ingredients in trout diets, including the whole rearing cycle.

Micromanaging metabolism-a role for miRNAs in teleost energy metabolism

MicroRNAs (miRNAs) are small, non-protein coding RNA sequences, which are found in most eukaryotes. Since their initial discovery, miRNAs have emerged as important regulators of many biological processes. One of the most important processes profoundly regulated by miRNAs is energy metabolism. Traditionally, metabolic functions of miRNAs have been studied in genome-sequenced mammalian organisms, especially the mouse model. However, partially driven by commercial interest in aquaculture, increasingly feasible large-scale molecular techniques have resulted in the characterization of miRNA repertoires, and importantly, several genome sequences of several (commercially important) teleost species, which also hold important roles as research models in the comparative physiology of energy metabolism. This review aims to introduce the recent advances in miRNA research in teleost fish and to describe the current knowledge of miRNA function in teleost energy metabolism. The most pressing research needs and questions to determine metabolic roles of miRNAs in teleost models are presented, as well as applicable technical approaches and current bottlenecks. Rainbow trout, which possess the advantages of newly available molecular tools and a long history as comparative research model in teleost energy metabolism, are discussed as a promising research model to address these questions.