How tryptophan levels in plant-based aquafeeds affect fish physiology, metabolism and proteome

An integrated study of glutamine alleviates enteritis induced by glycinin in hybrid groupers using transcriptomics, proteomics and microRNA analyses

Glutamine has been used to improve intestinal development and immunity in fish. We previously found that dietary glutamine enhances growth and alleviates enteritis in juvenile hybrid groupers (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂). This study aimed to further reveal the protective role of glutamine on glycinin-induced enteritis by integrating transcriptome, proteome, and microRNA analyses. Three isonitrogenous and isolipidic trial diets were formulated: a diet containing 10% glycinin (11S group), 10% glycinin diet supplemented with 2% alanine-glutamine (Gln group), and a diet containing neither glycinin nor alanine-glutamine (fishmeal, FM group). Each experimental diet was fed to triplicate hybrid grouper groups for 8 weeks. The analysis of intestinal transcriptomic and proteomics revealed a total of 570 differentially expressed genes (DEGs) and 169 differentially expressed proteins (DEPs) in the 11S and FM comparison group. Similarly, a total of 626 DEGs and 165 DEPs were identified in the Gln and 11S comparison group. Integration of transcriptome and proteome showed that 117 DEGs showed consistent expression patterns at both the transcriptional and translational levels in the Gln and 11S comparison group. These DEGs showed significant enrichment in pathways associated with intestinal epithelial barrier function, such as extracellular matrix (ECM)-receptor interaction, tight junction, and cell adhesion molecules (P < 0.05). Further, the expression levels of genes (myosin-11, cortactin, tenascin, major histocompatibility complex class I and II) related to these pathways above were significantly upregulated at both the transcriptional and translational levels (P < 0.05). The microRNA results showed that the expression levels of miR-212 (target genes colla1 and colla2) and miR-18a-5p (target gene colla1) in fish fed Gln group were significantly lower compared to the 11S group fish (P < 0.05). In conclusion, ECM-receptor interaction, tight junction, and cell adhesion molecules pathways play a key role in glutamine alleviation of hybrid grouper enteritis induced by high-dose glycinin, in which miRNAs and target mRNAs/proteins participated cooperatively. Our findings provide valuable insights into the RNAs and protein profiles, contributing to a deeper understanding of the underlying mechanism for fish enteritis.

Effects of the Replacement of Dietary Fish Meal with Poultry By-Product Meal on Growth and Intestinal Health of Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

To investigate the effect of poultry by-product meal (PBM) replacing fish meal on the growth and intestinal health of Chinese soft-shelled turtle (Pelodiscus sinensis). Four experimental diets were prepared. Fish meal was replaced by 0 (control group, PBM0), 5% (PBM5), 10% (PBM10), and 15% (PBM15) PBM. Compared to the control group, final body weight, weight gain, and specific growth rate were significantly increased, while feed conversion rate decreased significantly in the PBM10 group (p < 0.05). The PBM15 group significantly increased the moisture content and significantly decreased the ash content of the turtles (p < 0.05). The PBM5 and PBM15 groups significantly decreased the whole-body crude lipid (p < 0.05). The serum glucose content increased significantly in the PBM10 group (p < 0.05). The liver malonaldehyde content significantly decreased in the PBM5 group and in the PBM10 group (p < 0.05). Liver glutamic-oxalacetic transaminase and intestinal pepsin activity were increased significantly in the PBM15 group (p < 0.05). The expression of the intestinal interleukin 10 (IL-10) gene was significantly down-regulated in the PBM10 group and the PBM15 group (p < 0.05), the expression of the intestinal interferon-γ (IFN-γ), interleukin-8 (IL-8), and liver toll-like receptor 4 (TLR4) and toll-like receptor 5 (TLR5) genes were significantly up-regulated in the PBM5 group (p < 0.05). In summary, poultry by-product meal can be used as a protein source to replace fish meal in turtle feed. Based on quadratic regression analysis, the optimal replacement ratio is 7.39%.

DIGE Analysis of Fish Tissues

Two-dimensional difference gel electrophoresis (2D-DIGE) appears to be especially useful in quantitative approaches, allowing the co-separation of proteins of control samples and proteins of treated/disease samples on the same gel, eliminating gel-to-gel variability. The principle of 2D-DIGE is to label proteins prior to isoelectric focusing and use three spectrally resolvable fluorescent dyes, allowing the independent labeling of control and experimental samples. This procedure makes it possible to reduce the number of gels in an experiment, allowing the accurate and reproducible quantification of multiple samples. 2D-DIGE has been found to be an excellent methodical tool in several areas of fish research, including environmental pollution and toxicology, the mechanisms of development and disorders, reproduction, nutrition, evolution, and ecology.

Fish Processing and Digestion Affect Parvalbumins Detectability in Gilthead Seabream and European Seabass

Consumption of aquatic food, including fish, accounts for 17% of animal protein intake. However, fish consumption might also result in several side-effects such as sneezing, swelling and anaphylaxis in sensitized consumers. Fish allergy is an immune reaction to allergenic proteins in the fish muscle, for instance parvalbumin (PV), considered the major fish allergen. In this study, we characterize PV in two economically important fish species for southern European aquaculture, namely gilthead seabream and European seabass, to understand its stability during in vitro digestion and fish processing. This information is crucial for future studies on the allergenicity of processed fish products. PVs were extracted from fish muscles, identified by mass spectrometry (MS), and detected by sandwich enzyme-linked immunosorbent assay (ELISA) after simulated digestion and various food processing treatments. Secondary structures were determined by circular dichroism (CD) after purification by anion exchange and gel filtration chromatography. In both species, PVs presented as α-helical and β-sheet structures, at room temperature, were shown to unfold at boiling temperatures. In European seabass, PV detectability decreased during the simulated digestion and after 240 min (intestinal phase) no detection was observed, while steaming showed a decrease (p < 0.05) in PVs detectability in comparison to raw muscle samples, for both species. Additionally, freezing (−20 °C) for up to 12 months continued to reduce the detectability of PV in tested processing techniques. We concluded that PVs from both species are susceptible to digestion and processing techniques such as steaming and freezing. Our study obtained preliminary results for further research on the allergenic potential of PV after digestion and processing.

Species Differences in Tryptophan Metabolism and Disposition

Major species differences in tryptophan (Trp) metabolism and disposition exist with important physiological, functional and toxicity implications. Unlike mammalian and other species in which plasma Trp exists largely bound to albumin, teleosts and other aquatic species possess little or no albumin, such that Trp entry into their tissues is not hampered, neither is that of environmental chemicals and toxins, hence the need for strict measures to safeguard their aquatic environments. In species sensitive to toxicity of excess Trp, hepatic Trp 2,3-dioxygenase (TDO) lacks the free apoenzyme and its glucocorticoid induction mechanism. These species, which are largely herbivorous, however, dispose of Trp more rapidly and their TDO is activated by smaller doses of Trp than Trp-tolerant species. In general, sensitive species may possess a higher indoleamine 2,3-dioxygenase (IDO) activity which equips them to resist immune insults up to a point. Of the enzymes of the kynurenine pathway beyond TDO and IDO, 2-amino-3-carboxymuconic acid-6-semialdehyde decarboxylase (ACMSD) determines the extent of progress of the pathway towards NAD⁺ synthesis and its activity varies across species, with the domestic cat (Felis catus) being the leading species possessing the highest activity, hence its inability to utilise Trp for NAD⁺ synthesis. The paucity of current knowledge of Trp metabolism and disposition in wild carnivores, invertebrates and many other animal species described here underscores the need for further studies of the physiology of these species and its interaction with Trp metabolism.

An Emerging Cross-Species Marker for Organismal Health: Tryptophan-Kynurenine Pathway

Tryptophan (TRP) is an essential dietary amino acid that, unless otherwise committed to protein synthesis, undergoes metabolism via the Tryptophan-Kynurenine (TRP-KYN) pathway in vertebrate organisms. TRP and its metabolites have key roles in diverse physiological processes including cell growth and maintenance, immunity, disease states and the coordination of adaptive responses to environmental and dietary cues. Changes in TRP metabolism can alter the availability of TRP for protein and serotonin biosynthesis as well as alter levels of the immune-active KYN pathway metabolites. There is now considerable evidence which has shown that the TRP-KYN pathway can be influenced by various stressors including glucocorticoids (marker of chronic stress), infection, inflammation and oxidative stress, and environmental toxicants. While there is little known regarding the role of TRP metabolism following exposure to environmental contaminants, there is evidence of linkages between chemically induced metabolic perturbations and altered TRP enzymes and KYN metabolites. Moreover, the TRP-KYN pathway is conserved across vertebrate species and can be influenced by exposure to xenobiotics, therefore, understanding how this pathway is regulated may have broader implications for environmental and wildlife toxicology. The goal of this narrative review is to (1) identify key pathways affecting Trp-Kyn metabolism in vertebrates and (2) highlight consequences of altered tryptophan metabolism in mammals, birds, amphibians, and fish. We discuss current literature available across species, highlight gaps in the current state of knowledge, and further postulate that the kynurenine to tryptophan ratio can be used as a novel biomarker for assessing organismal and, more broadly, ecosystem health.

Fish Allergenicity Modulation Using Tailored Enriched Diets—Where Are We?

Food allergy is an abnormal immune response to specific proteins in a certain food. The chronicity, prevalence, and the potential fatality of food allergy, make it a serious socio-economic problem. Fish is considered the third most allergenic food in the world, affecting part of the world population with a higher incidence in children and adolescents. The main allergen in fish, responsible for the large majority of fish-allergic reactions in sensitized patients, is a small and stable calcium-binding muscle protein named beta-parvalbumin. Targeting the expression or/and the 3D conformation of this protein by adding specific molecules to fish diets has been the innovative strategy of some researchers in the fields of fish allergies and nutrition. This has shown promising results, namely when the apo-form of β-parvalbumin is induced, leading in the case of gilthead seabream to a 50% reduction of IgE-reactivity in fish allergic patients.

Alternative Proteins for Fish Diets: Implications beyond Growth

Aquaculture has been challenged to find alternative ingredients to develop innovative feed formulations that foster a sustainable future growth. Given the most recent trends in fish feed formulation on the use of alternative protein sources to decrease the dependency of fishmeal, it is fundamental to evaluate the implications of this new paradigm for fish health and welfare. This work intends to comprehensively review the impacts of alternative and novel dietary protein sources on fish gut microbiota and health, stress and immune responses, disease resistance, and antioxidant capacity. The research results indicate that alternative protein sources, such as terrestrial plant proteins, rendered animal by-products, insect meals, micro- and macroalgae, and single cell proteins (e.g., yeasts), may negatively impact gut microbiota and health, thus affecting immune and stress responses. Nevertheless, some of the novel protein sources, such as insects and algae meals, have functional properties and may exert an immunostimulatory activity. Further research on the effects of novel protein sources, beyond growth, is clearly needed. The information gathered here is of utmost importance, in order to develop innovative diets that guarantee the production of healthy fish with high quality standards and optimised welfare conditions, thus contributing to a sustainable growth of the aquaculture industry.

The PeptideAtlas of a widely cultivated fish Labeo rohita: A resource for the Aquaculture Community

Labeo rohita (Rohu) is one of the most important fish species produced in world aquaculture. Integrative omics research provides a strong platform to understand the basic biology and translate this knowledge into sustainable solutions in tackling disease outbreak, increasing productivity and ensuring food security. Mass spectrometry-based proteomics has provided insights to understand the biology in a new direction. Very little proteomics work has been done on 'Rohu' limiting such resources for the aquaculture community. Here, we utilised an extensive mass spectrometry based proteomic profiling data of 17 histologically normal tissues, plasma and embryo of Rohu to develop an open source PeptideAtlas. The current build of "Rohu PeptideAtlas" has mass-spectrometric evidence for 6015 high confidence canonical proteins at 1% false discovery rate, 2.9 million PSMs and ~150 thousand peptides. This is the first open-source proteomics repository for an aquaculture species. The 'Rohu PeptideAtlas' would promote basic and applied aquaculture research to address the most critical challenge of ensuring nutritional security for a growing population.

Effect of creatine and EDTA supplemented diets on European seabass (Dicentrarchus labrax) allergenicity, fish muscle quality and omics fingerprint

The relatively easy access to fish worldwide, alongside the increase of aquaculture production contributes to increased fish consumption which result in higher prevalence of respective allergies. Allergies to fish constitute a significant concern worldwide. β-parvalbumin is the main elicitor for IgE-mediated reactions. Creatine, involved in the muscle energy metabolism, and ethylenediamine tetraacetic acid (EDTA), a calcium chelator, are potential molecules to modulate parvalbumin. The purpose of this study was to test creatine (2, 5 and 8%) and EDTA (1.5, 3 and 4.5%) supplementation in fish diets to modulate β-parvalbumin expression and structure and its allergenicity in farmed European seabass (Dicentrarchus labrax) while assessing its effects on the end-product quality. Fish welfare and muscle quality parameters were evaluated by plasma metabolites, rigor mortis, muscle pH and sensory and texture analysis. Proteomics was used to assess alterations in muscle proteome profile and metabolic fingerprinting by Fourier transform infrared spectroscopy was used to assess the liver metabolic profile. In addition, IgE-reactivity to parvalbumin was analysed using fish allergic patient sera. Metabolic fingerprinting of liver tissue revealed no major alterations in infrared spectra with creatine supplementation, while with EDTA, only absorption bands characteristic of lipids were altered. Comparative proteomics showed up regulation of (tropo) myosin and phosphoglycerate mutase 2 with Creatine supplementation. In the case of EDTA proteomics showed up regulation of proteins involved in cellular and ion homeostasis. Allergenicity seems not to be modulated with creatine or EDTA supplementation as no decreased expression levels were found and IgE-binding reactivity showed no quantitative differences.

Effect of papaya (Carica papaya) leaf extract as dietary growth promoter supplement in red hybrid tilapia (Oreochromis mossambicus × Oreochromis niloticus) diet

The purpose of this experiment was to examine the potential use of Carica papaya leaf extract as a supplement to promote growth and improve feed utilization in red hybrid tilapia. Five diets were formulated containing isolipidic (80 g/kg) and isonitrogenic (350 g/kg) levels. All feeds contained similar types and amounts of raw materials but differed in the inclusion of papaya leaf extract (0, 5, 10, 20 and 40 g/kg feed). The initial size of fish used was 2.3 ± 0.01 g. Each diet was performed in triplicate tanks, and the feeding period was 12 weeks. Fish fed diet containing 2% papaya leaf extract (PLE) had the highest final weight, 31.14 ± 1.47 g, followed by 1% PLE (27.27 ± 1.75 g). These two diets (1% and 2%) were also showed significant improvements of weight gain, SGR, and feed efficiency of the red hybrid tilapia (p < 0.05). However, papaya leaf extract did not affect the HSI, VSI, PER, digestive enzymes activity, blood composition, and survival rate. Supplementing the diets with papaya leaf extract lowered serum urea. Findings of this research suggest that adding papaya leaf extract to the diet of red hybrid tilapia improves growth and feed efficiency without adversely affecting blood parameters. Therefore, an inclusion level between 1% and 2% of the papaya leaf extract is recommended as a feed additive to promote red hybrid tilapia fry growth.

The Evaluation of Arthrospira platensis Bioactivity and their Dietary Supplementation to Nile Tilapia Vegetarian Diet on Growth Performance, Feed Utilization, Body Composition and Hemato-Biochemical Parameters

The present study aimed to identify the carotenoid content and evaluate the antioxidant activities of spirulina, Arthrospira platensis (in vitro), and the effect of its supplementation to a vegetarian diet on growth performance, feed utilization, body proximate composition and physiological status of Nile tilapia, Oreochromis niloticus (in vivo). The carotenoid content of spirulina was identified by UPLC-MS/MS and showed that trans and cis β-carotene were the major carotenoids (88.3%) followed by β-cryptoxanthin and zeaxanthin. The antioxidant activity of spirulina was determined in water and crude carotenoid extracts by 2,2-diphenyl-1-picryhydrazyl (DPPH) scavenging assay, both extracts showed a significant free radical scavenging capacity. In addition, Nile tilapia fry (0.83 ± 0.01 g) was fed a vegetarian diet supplemented with different levels of spirulina for 12 weeks. The results revealed that the highest growth performance and nutrient utilization were recorded with 0.5% spirulina and the peak response determined at 0.63%-0.65% using polynomial second order regression. Also, the hemoglobin content improved in a quadratic regression model with the peak at 0.67% spirulina. Plasma total protein and lipid contents increased significantly with spirulina levels over 0.50%. Moreover, the aminopeptidase activities and glucose level decreased significantly with increasing spirulina levels. The current study recommended the supplementation of the Nile tilapia vegetarian diet with spirulina at levels of 0.63-0.65% for better growth performance and physiological status.

Effect of Dietary Tryptophan on Growth, Intestinal Microbiota, and Intestinal Gene Expression in an Improved Triploid Crucian Carp

Tryptophan (Trp) has received increasing attention in the maintenance of intestinal function. In this study, improved triploid crucian carp (ITCC) fed diets containing 6.35 g kg⁻¹ Trp had higher average daily gain (ADG) and improved villus height (VH) and crypt depth (CD) in the intestine compared to the control group. To elucidate the potential mechanisms, we used RNA sequencing (RNA-seq) to investigate changes in the intestinal transcriptome and 16S rRNA gene sequencing to measure the intestinal microbiota in response to 6.35 g kg⁻¹ Trp feeding in ITCC. Dietary Trp altered intestinal gene expression involved in nutrient transport and metabolism. Differentially expressed transcripts (DETs) were highly enriched in key pathways containing protein digestion and absorption and the AMPK signaling pathway. 16S rRNA sequencing showed that 6.35 g kg⁻¹ Trp significantly increased the abundance of the genus Cetobacterium, and the Firmicutes/Bacteroidetes ratio at the phylum level (P < 0.05). In addition, bacterial richness indices (Simpson index) significantly increased (P < 0.05) community evenness in response to 6.35 g kg⁻¹ Trp. In conclusion, appropriate dietary Trp improves the growth performance, and influences the intestinal flora of ITCC. This study might be helpful to guide the supply of dietary exogenous Trp in ITCC breeding.

Evaluating the impact of methionine-enriched diets in the liver of European seabass through label-free shotgun proteomics

Plant protein sources play an essential role in aquaculture by reducing the use of fish meal to sustainable levels, although further supplementation is needed to fulfill fish nutritional requirements. This work addressed fish growth performance and proteome changes to dietary methionine in European seabass juveniles. A dose-dependent response to methionine (Met) was observed on fish growth consistent with proteomic analyses, suggesting Met requirement ≥0.9% (w/w). Fish fed at 0.77% (w/w) exhibited reduced growth and an enrichment in proteins involved in cellular homeostasis. Proteomics data suggest an optimal nutritional status at 1.36% Met (w/w), together with putative beneficial effects on the immune system up to 1.66% Met (w/w). The response to dietary Met involved the convergence of different metabolic and signalling pathways implicated in cell growth and immune response e.g., mTOR, Hedgehog or the T Cell receptor signalling, coupled with a fine-tuning regulation of amino acid metabolism and translation.