The effects of dietary leucine on the growth performances, body composition, metabolic abilities and innate immune responses in black carp Mylopharyngodon piceus

The Effects of Fishmeal Replacement with Degossypolled Cottonseed Protein on Growth, Serum Biochemistry, Endocrine Responses, Lipid Metabolism, and Antioxidant and Immune Responses in Black Carp (Mylopharyngodon piceus)

This research investigated the growth, serum biochemistry, antioxidant capability, and immunity impact of black carp fed degossypolled cottonseed protein replacing fishmeal at the levels of 0%, 10%, 20%, 30%, 40%, and 50% (DCP0, DCP10, DCP20, DCP30, DCP40, and DCP50), respectively. The results showed there were no significant changes in growth among these test groups. The activities and mRNA expression levels of amylase and trypsin were heightened in conjunction with 30-40% DCP. Although the insulin contents were reduced with a rise in DCP content, 5-hydroxytryptamino was increased in the DCP40 and DCP50 groups. DCP40 could heighten the levels of low-density lipoprotein cholesterol, triglycerides, total cholesterol, and urea nitrogen. Although lower levels of DCP (≤20%) could increase the total antioxidant capacity compared with the DCP50 group, DCP50 could markedly heighten levels of catalase, glutathione S-transferase, H2O2, and malondialdehyde. Meanwhile, the mRNA levels of Mn-superoxide dismutase, glutathione reductase, glutathione peroxidase, glutamate-cysteine ligase regulatory subunit, and nuclear factor E2-related factor 2 were heightened in the DCP30 group compared with the DCP50 group. The levels of alkaline phosphatase, immunoglobulin M, and liver-expressed antimicrobial peptide 2 were markedly heightened in the liver of the DCP20 group compared with the DCP50 group. In conclusion, a suitable level of DCP (20%) could improve serum biochemical indices and hormone variation, enhance antioxidant capability, and increase immunity in black carp.

Hematological and blood biochemical responses of Colossoma macropomum and Piaractus brachypomus subjected to sudden temperature reduction and thermal readjustment

This study aimed to evaluate the physiological responses of Colossoma macropomum and Piaractus brachypomus, faced with a sudden reduction in temperature followed by thermal readjustment. Forty juveniles of each species were fasted for 24 h, after which, ten fish of each species were used as a basal group, while the others were subjected to a sudden temperature reduction from 28.7 to 18.6 °C and maintained in that condition for 24 h. The temperature was then restored, and the fish were observed for another 24 h of readjustment (R). Blood was collected at 1hATC, 24hATC and 24hR (ATC = after temperature change). There was no mortality during the experiment. C. macropomum showed a decrease in glucose without recovery after thermal readjustment, unlike P. brachypomus which experienced an increase at 1hATC. In both, C. macropomum and P. brachypomus, the lowest triglycerides levels were observed at 1hATC, with no return to the initial condition at 24hATC and 24hR. Cholesterol levels in both species showed reductions at 1hATC and 24hATC; however, there was a return to the initial condition at 24hR. The abrupt temperature change caused a reduction in lactate levels at 1hATC and 24hATC; however, only P. brachypomus returned to the initial levels. Plasma chloride was highest at 24hR and lowest at 1hATC, for both species. Therefore, we observed that the sudden drop in temperature, followed by thermal readjustment caused physiological changes, and P. brachypomus demonstrated a greater capacity to reestablish the initial condition of shape during thermal readjustment.

Exploring the novel benefits of leucine: Protecting nitrite-induced liver damage in sub-adult grass carp (Ctenopharyngodon idella) through regulating mitochondria quality control

Leucine is an essential amino acid for fish. The ability of leucine to resist stress in fish has not been reported. Nitrite is a common pollutant in the aquatic environment. Therefore, we investigated the effects of dietary leucine on growth performance and nitrite-induced liver damage, mitochondrial dysfunction, autophagy, and apoptosis for sub-adult grass carp. A total of 450 grass carp (615.91 ± 1.15 g) were selected and randomly placed into 18 net cages. The leucine contents of the six diets were 2.91, 5.90, 8.92, 11.91, 14.93, and 17.92 g/kg, respectively. After a 9-week feeding trial, the nitrite exposure experiment was set up for 96 h. These results indicated that dietary leucine significantly promoted FW, WG, PWG, and SGR of sub-adult grass carp (P < 0.05). Appropriate levels of dietary leucine (11.91-17.92 g/kg) decreased the activities of serum parameters (glucose, cortisol, and methemoglobin contents, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and lactate dehydrogenase), the contents of reactive oxygen species (ROS), nitric oxide (NO) and peroxynitrite (ONOO-). In addition, appropriate levels of dietary leucine (11.91-17.92 g/kg) increased the mRNA levels of mitochondrial biogenesis genes (PGC-1α, Nrf1/2, TFAM), fusion-related genes (Opa1, Mfn1/2) (P < 0.05), and decreased the mRNA levels of caspase 3, caspase 8, caspase 9, fission-related gene (Drp1), mitophagy-related genes (Pink1, Parkin) and autophagy-related genes (Beclin1, Ulk1, Atg5, Atg7, Atg12) (P < 0.05). Appropriate levels of dietary leucine (8.92-17.92 g/kg) also increased the protein levels of AMP-activated protein kinase (AMPK), prostacyclin (p62) and decreased the protein levels of protein light chain 3 (LC3), E3 ubiquitin ligase (Parkin), and Cytochrome c (Cytc). Appropriate levels of leucine (8.92-17.92 g/kg) could promote growth performance and alleviate nitrite-induced mitochondrial dysfunction, autophagy, apoptosis for sub-adult grass carp. Based on quadratic regression analysis of PWG and serum GPT activity, dietary leucine requirements of sub-adult grass carp were recommended to be 12.47 g/kg diet and 12.55 g/kg diet, respectively.

Hematological, biochemical and oxidative responses induced by thermal shock in juvenile Tambaqui (Colossoma macropomum) and its hybrid Tambatinga (Colossoma macropomum x Piaractus brachypomus)

The effects of thermal shock on hematological, biochemical and antioxidant responses were evaluated in liver tissue of juvenile tambaqui (Colossoma macropomum) and tambatinga (♀ C. macropomum × ♂ Piaractus brachypomus). Forty juveniles of tambaqui and 40 juveniles of tambatinga, of the same age and with an initial weight of 23.3 ± 6.7 g, were randomly distributed in eight 28L circular tanks. A tank (n = 10 fish) of tambaqui and a tank (n = 10 fish) of tambatinga were then used to obtain basal data. The other animals were subjected to thermal shock with sudden temperature reduction from 28 to 18 ºC. Blood and tissue were then collected after 1, 6 and 24 h from the onset of thermal shock. No mortality was observed during the experimental period. Thermal shock increased triglyceride levels after 24 h of stress for tambaqui and reduced values for tambatinga. There was an effect on plasma glucose only for fish group (P < 0.0001) and collection time (P < 0.0001) with a peak observed for the hybrid after 6 h. The interaction of factors for SOD indicated greater activity for tambatinga at the 6 h collection and lower at basal and 1 h collections. There was an interaction for CAT (P = 0.0020) with less activity for tambatinga at 1 h. However, thermal shock and hybridization did not influence GST and TBARS levels in liver tissue. Therefore, the results suggest that the hybrid, tambatinga, is more efficient at promoting adjustments of biochemical responses and antioxidant enzymes during thermal shock.

Selenium yeast improve growth, serum biochemical indices, metabolic ability, antioxidant capacity and immunity in black carp Mylopharyngodnpiceus

This experiment was conducted to investigate the impacts of dietary selenium yeast (SeY) on the growth performance, fish body composition, metabolic ability, antioxidant capability, immunity and inflammatory responses in juvenile black carp (Mylopharyngodn piceus). The base diet was supplemented with 0.00, 0.30 and 0.60 g/kg SeY (0.04, 0.59 and 1.15 mg/kg of selenium) to form three isonitrogenous and isoenergetic diets for juvenile black carp with a 60-day. Adequate dietary SeY (0.30 and 0.60 g/kg) could significantly increase the weight gain (WG), special growth rate (SGR) compared to the SeY deficient groups (0.00 g/kg) (P < 0.05). Meanwhile, 0.30 and 0.60 g/kg SeY elevated the mRNA levels of selenoprotein T2 (SEPT2), selenoprotein H (SEPH), selenoprotein S (SEPS) and selenoprotein M (SEPM) in the liver and intestine compared with the SeY deficient groups (P < 0.05). Adequate dietary SeY could promote glucose catabolism and utilization through activating glucose transport (GLUT2), glycolysis (GCK, HK, PFK, PK, PDH), tricarboxylic acid cycle (ICDH and MDH), glycogen synthesis (LG, GCS and GBE) and IRS/PI3K/AKT signal pathway molecules (IRS2b, PI3Kc and AKT1) compared with the SeY deficient groups (P < 0.05). Similarly, adequate dietary SeY could improve lipid transport and triglycerides (TG) synthesis through increasing transcription amounts of CD36, GK, DGAT, ACC and FAS in the fish liver compared with the SeY deficient groups (P < 0.05). In addition, adequate SeY could markedly elevate activities of antioxidant enzymes (T-SOD, CAT, GR, GPX) and contents of T-AOC and GSH, while increased transcription amounts of Nrf2, Cu/Zn-SOD, CAT, and GPX in fish liver and intestine (P < 0.05). However, adequate SeY notably decreased contents of MDA, and the mRNA transcription levels of Keap1 in the intestine compared with the SeY deficient groups (P < 0.05). Adequate SeY markedly increased amounts or levels of the immune factors (ALP, ACP, LZM, C3, C4 and IgM) and the transcription levels of innate immune-related functional genes in the liver and intestine (LZM, C3 and C9) compared to the SeY deficient groups (P < 0.05). Moreover, adequate SeY could notably reduce levels of IL-8, IL-1β, and IFN-γ and elevate TGF-1β levels in fish intestine (P < 0.05). The transcription levels of MAPK13, MAPK14 and NF-κB p65 were notably reduced in fish intestine treated with 0.30 and 0.60 g/kg SeY (P < 0.05). In conclusion, these results suggested that 0.30 and 0.60 g/kg SeY could not only improve growth performance, increase Se, glucose and lipid metabolic abilities, enhance antioxidant capabilities and immune responses, but also alleviate inflammation, thereby supplying useful reference for producing artificial feeds in black carp.

Dietary leucine supplementation improves growth performance, metabolic responses of liver via GCN2/ATF4, and insulin signaling pathways in largemouth bass (Micropterus salmoides)

An 8-week growth experiment was conducted to investigate the effects of dietary leucine on growth performance, body composition, and gene expression of hepatic nutrient metabolism in the largemouth bass (Micropterus salmoides). Six isonitrogenous (49.87%) diets with graded leucine levels (2.62, 3.07, 3.60, 3.87, 4.20, 4.71% of dry diet) were fed to triplicate groups with 20 juvenile fish (20.00 ± 0.13 g). The results revealed that the specific growth rate (SGR) and weight gain (WG) increased significantly with increasing dietary leucine levels, reached their maximal value in the Leu-4.20% groups, and then decreased slightly. Although the feed conversion ratio (FCR) showed decreasing trends, no significant difference was detected. Leucine supplementation significantly improved the content of body protein and total plasma protein (TP). Additionally, a higher expression level of target of rapamycin (TOR) and ribosomal protein S6 (S6) mRNA was observed in the Leu-3.87% and Leu-4.20% diets, whereas the GCN2 (general control nonderepressible2 kinase) and AFT4 (activating transcription factor 4) mRNA expression levels were suppressed. The lipid content of the body was not influenced by leucine levels, whereas the content of total triglyceride (TG) first decreased significantly with increasing dietary leucine levels from 2.62 to 3.87% and then increased with increasing leucine levels (4.20% to 4.71%). The total cholesterol (TC) and low-density lipoproteins (LDL) trended in a similar direction but did not achieve statistical significance (P > 0.05). The expression of insulin receptor substrate 1 (IRS-1) was significantly elevated by dietary leucine levels, while protein kinase B (AKT) and phosphatidylinositol 3-kinase (PI3K) expression was inconsistently upregulated. Furthermore, leucine supplementation decreased plasma glucose and hepatic glycogen contents, and the expression levels of glucokinase (GK), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G6pase) were significantly inhibited at 4.20% and 4.71% leucine diets. Analyses of the change in SGR and FCR using the quadratic regression model estimated that the optimum dietary leucine requirement of juvenile largemouth bass was 4.42% and 4.63% of the dry diet (8.86% and 9.28% of dietary protein), respectively.

Effects of dietary leucine on growth, antioxidant capacity, immune response, and inflammation in juvenile yellow catfish Pelteobagrus fulvidraco

The experiment was conducted to investigate the effects of dietary leucine on growth, antioxidant capacity, immune response, and inflammation in juvenile yellow catfish. Five diets were formulated to contain five dietary leucine levels: 12.00 (control), 19.00, 26.00, 33.00, and 40.00 g kg-1. Each diet was randomly assigned to triplicate groups of 30 juvenile fish (5.02 ± 0.15 g) twice daily to apparent satiation for 56 days. Weight gain rate, specific growth rate, and activities of liver superoxide dismutase, glutathione peroxidase, and serum lysozyme, as well as immunoglobulin M content, significantly increased with increase in dietary leucine levels up to 26.00 g kg-1, but those values decreased significantly with a further increase in dietary leucine. On the contrary, the lowest malondialdehyde content was found in 26.00 and 33.00 g kg-1 leucine groups. The expression levels of IGF 1 and MYF 5 genes in muscle were significantly upregulated with increase in dietary leucine levels up to 26.00 g kg-1, but the expression of MSTN level showed the opposite trend. The lowest expression levels of IL 8 and TNFɑ genes in the liver were found in 26.00 g kg-1 leucine groups. The quadratic regression analysis on weight gain, specific growth rate, and feed conversion ratio against dietary leucine levels indicated that the optimal dietary leucine requirement was estimated to be 26.84-27.00 g kg-1of the dry diet.

Dietary Soybean Lecithin Improves Growth, Immunity, Antioxidant Capability and Intestinal Barrier Functions in Largemouth Bass Micropterus salmoides Juveniles

This study evaluated the effects of dietary soybean lecithin (SBL) on the growth, haematological indices, immunities, antioxidant capabilities, and inflammatory and intestinal barrier functions because little information of dietary SBL could be obtained in juvenile largemouth bass (Micropterus salmoides). The fish were fed identical diets except for SBL added at 0, 2, 4 and 8%. It was found that 4 and 8% SBL significantly increased fish weight gain and daily growth rate (p < 0.05), while 4% SBL was optimal for enhancing RBC, HGB, PLT, MCV, MCH, WBC and MON in blood, and ALB and ALP in serum (p < 0.05). SBL (4%) also significantly elevated the antioxidant enzymes activities of T-SOD, CAT, GR, GPx, GST and T-AOC and GSH contents; increased mRNA transcription levels of Nrf2, Cu/Zn-SOD, CAT, GR, GST3 and GPx3; and decreased MDA contents. Keap1a and Keap1b levels were markedly down-regulated (p < 0.05). SBL (4%) significantly enhanced levels of the immune factors (ACP, LZM and C3) and the mRNA expression levels of innate immune-related genes (C3, C4, CFD, HEPC and MHC-I) compared with the control groups (0%) (p < 0.05). SBL (4%) significantly increased IgM and T-NOS in the intestine (p < 0.05) and significantly decreased levels of TNF-α, IL-8, IL-1β and IFN-γ and increased TGF-β1 at both transcription and protein levels in the liver and intestine (p < 0.05). The mRNA expression levels of MAPK13, MAPK14 and NF-κB P65 were significantly decreased in the intestine in the 4% SBL groups (p < 0.05). Histological sections also demonstrated that 4% SBL protected intestinal morphological structures compared with controls. This included increased intestinal villus height and muscular thickness (p < 0.05). Furthermore, the mRNA expression levels of the intestinal epithelial cell tight junction proteins (TJs) (ZO-1, claudin-3, claudin-4, claudin-5, claudin-23 and claudin-34) and mucin-5AC were significantly up-regulated in the 4% SBL groups compared with the controls (p < 0.05). In conclusion, these results suggested that 4% dietary SBL could not only improve growth, haematological indices, antioxidant capabilities, immune responses and intestinal functions, but also alleviate inflammatory responses, thereby providing reference information for the feed formulations in cultured largemouth bass.

Comparison and Correlation Analysis of Immune Function and Gut Microbiota of Broiler Chickens Raised in Double-Layer Cages and Litter Floor Pens

This study aimed to compare the immune function and gut microbiota between double-layer caged and litter floor pen-raised broiler chickens. Eighty meaty male chicks were selected and divided into cage group and litter floor group, with 20 replicates in each group. The broilers were raised in the same chicken house. The rearing density of the two rearing systems was same. The broilers were sampled on days 13 and 34. The results showed that compared with the cage group, the litter floor broilers had worse growth performance (23.24% increase in feed conversion ratio) in the early stage; better slaughter performance at day 42; stronger peripheral immune function (including higher lysozyme activity, T-cell ratio, Th-cell ratio, Tc-cell ratio, CD4/CD8, IL-10, B-cell ratio, IgG and IgA levels; and spleen immune-related gene expression); and stronger intestinal immune function (including higher ileum CD80, AvBD2, Mucin2, NF-κB, IL-8, IFN-γ/IL-4, and IgA mRNA expression levels and ileal mucosa sIgA levels). Compared with the cage group, the alpha diversity of ileum microbiota of the litter floor broilers was higher, and the relative abundance levels of litter breeding bacteria (Facklamia, Globicatella, and Jeotgalicoccus) and potential pathogenic bacteria (Streptococcus and Staphylococcus) were higher (P < 0.05). Through Spearman correlation analysis, it was found that enriched microbes in the ileum of litter floor broilers were positively correlated with immune function. In summary, compared with cage broilers, litter floor broilers had more potential pathogenic bacteria and litter breeding bacteria in the ileum, which may be one of the important reasons for the stronger immune function status. IMPORTANCE In China, the three-dimensional rearing system (cage) for broilers has gradually become a trend. In production, it was found that the incidence of disease in broiler chickens raised in cage systems was significantly higher than that of ground litter. Given that broilers raised on ground litter systems may be exposed to more environmental microbes, it is important to understand whether the rearing environment affects the function and status of the host immune system by altering the gut microbiota. In this study, rearing environment-derived gut microbes associated with stronger immune function in ground litter broilers were provided, which will provide new insights into strategies to target gut microbes to promote immune function and status in broilers raised in cages.

Ultra-Performance Liquid Chromatography-Mass Spectrometry-Based Untargeted Metabolomics Reveals the Key Potential Biomarkers for Castor Meal-Induced Enteritis in Juvenile Hybrid Grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂)

The intensification of aquaculture to help kerb global food security issues has led to the quest for more economical new protein-rich ingredients for the feed-based aquaculture since fishmeal (FM, the ingredient with the finest protein and lipid profile) is losing its acceptability due to high cost and demand. Although very high in protein, castor meal (CM), a by-product after oil-extraction, is disposed-off due to the high presence of toxins. Concurrently, the agro-industrial wastes’ consistent production and disposal are of utmost concern; however, having better nutritional profiles of these wastes can lead to their adoption. This study was conducted to identify potential biomarkers of CM-induced enteritis in juvenile hybrid-grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂) using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) alongside their growth and distal intestinal (DI) health evaluation. A total of 360 fish (initial weight = 9.13 ± 0.01g) were randomly assigned into three groups, namely, fish-meal (FM) (control), 4% CM (CM4), and 20% CM (CM20). After the 56-days feeding-trial, the DI tissues of FM, CM4, and CM20 groups were collected for metabolomics analysis. Principal components analysis and partial least-squares discriminant-analysis (PLS-DA, used to differentiate the CM20 and CM4, from the FM group with satisfactory explanation and predictive ability) were used to analyze the UPLC-MS data. The results revealed a significant improvement in the growth, DI immune responses and digestive enzyme activities, and DI histological examinations in the CM4 group than the others. Nonetheless, CM20 replacement caused DI physiological damage and enteritis in grouper as shown by AB-PAS staining and scanning electron microscopy examinations, respectively. The most influential metabolites in DI contents identified as the potential biomarkers in the positive and negative modes using the metabolomics UPLC-MS profiles were 28 which included five organoheterocyclic compounds, seven lipids, and lipid-like molecules, seven organic oxygen compounds, two benzenoids, five organic acids and derivatives, one phenylpropanoids and polyketides, and one from nucleosides, nucleotides, and analogues superclass. The present study identified a broad array of DI tissue metabolites that differed between FM and CM diets, which provides a valuable reference for further managing fish intestinal health issues. A replacement level of 4% is recommended based on the growth and immunity of fish.

Dietary valine improved growth, immunity, enzymatic activities and expression of TOR signaling cascade genes in rainbow trout, Oncorhynchus mykiss fingerlings

This study was conducted to determine the effects of dietary valine (Val) on growth, hemato-biochemical parameters, immunity, enzymatic activities, antioxidant status and expression of target of rapamycin (TOR) and 4E-BP genes in rainbow trout, Oncorhynchus mykiss (1.57 ± 0.03 g; 5.10 ± 0.34 cm). Six isonitrogenous (450 g kg⁻¹) and isoenergetic (20.90 kJ 100 g⁻¹_, gross energy) diets were designed to represent varied Val levels (10.5, 13.0, 15.5, 18.0, 20.5 and 23.0 g kg⁻¹ dry diet basis). Growth parameters improved significantly (P < 0.05) with the amelioration of dietary Val level up to 18.0 g kg⁻¹. Highest (P < 0.05) body protein content was noted at 18.0 g kg⁻¹ dietary Val. Significant differences in hematological, intestinal enzymatic activities and antioxidant parameters were noted. However, plasma variables did not show any significant differences except aspartate transaminase and uric acid. Total protein content increased significantly, while the albumin and globulin content did not show any significant (P > 0.05) difference. Moreover expression of TOR mRNA and elF4E-binding protein (4E-BP) was observed higher (P < 0.05) at 18.0 g kg⁻¹ Val. On the basis of results, optimum dietary Val requirement for maximal growth of rainbow trout was determined to be 18.19 g kg⁻¹ of dry diet, corresponding to 40.42 g kg⁻¹ of dietary protein.

Asian carp: A threat to American lakes, a feast on Chinese tables

Asian carp, which are widely distributed in Asia and Europe, are nutritious and popular with consumers. In China, Asian carp is a tasty dish and has been consumed for thousands of years. However, they are considered aggressive invasive species that threaten rivers, lakes, and indigenous species in the United States. Asian carp have proliferated greatly in the water basin of the Mississippi River and its tributaries, and they have caused severe ecological problems over the past 20 years. In recent years, several state governments along the Mississippi River have implemented assistance programs to eliminate invasive Asian carp, but these did not alleviate the threat. We conducted a survey to understand consumers' attitudes toward Asian carp in the United States, and related reports were reviewed to explore the possibility of Asian carp as food fish on American tables. Emphasis is placed on the farming history, functional characteristics, consumption preferences, and successful utilization methods for Asian carp in China. In addition, suggestions and possible utilization methods were proposed to improve the negative impression of Asian carp in the United States. Further research is needed to take full advantage of this huge excellent source of food or health supplements. This review provides ideas and directions for the use of Asian carp in the United States. We believe that through effective cooperation between China and the United States, the negative aspects of Asian carp in the United States could be diminished, and a mutually beneficial situation could be achieved.

Nutrition and Functions of Amino Acids in Fish

Aquaculture is increasingly important for providing humans with high-quality animal protein to improve growth, development and health. Farm-raised fish and shellfish now exceed captured fisheries for foods. More than 70% of the production cost is dependent on the supply of compound feeds. A public debate or concern over aquaculture is its environmental sustainability as many fish species have high requirements for dietary protein and fishmeal. Protein or amino acids (AAs), which are the major component of tissue growth, are generally the most expensive nutrients in animal production and, therefore, are crucial for aquatic feed development. There is compelling evidence that an adequate supply of both traditionally classified nutritionally essential amino acids (EAAs) and non-essential amino acids (NEAAs) in diets improve the growth, development and production performance of aquatic animals (e.g., larval metamorphosis). The processes for the utilization of dietary AAs or protein utilization by animals include digestion, absorption and metabolism. The digestibility and bioavailability of AAs should be carefully evaluated because feed production processes and AA degradation in the gut affect the amounts of dietary AAs that enter the blood circulation. Absorbed AAs are utilized for the syntheses of protein, peptides, AAs, and other metabolites (including nucleotides); biological oxidation and ATP production; gluconeogenesis and lipogenesis; and the regulation of acid-base balance, anti-oxidative reactions, and immune responses. Fish producers usually focus on the content or digestibility of dietary crude protein without considering the supply of AAs in the diet. In experiments involving dietary supplementation with AAs, inappropriate AAs (e.g., glycine and glutamate) are often used as the isonitrogenous control. At present, limited knowledge is available about either the cell- and tissue-specific metabolism of AAs or the effects of feed processing methods on the digestion and utilization of AAs in different fish species. These issues should be addressed to develop environment-friendly aquafeeds and reduce feed costs to sustain the global aquaculture.

Effects of dietary leucine levels on intestinal antioxidant status and immune response for juvenile golden pompano (Trachinotus ovatus) involved in Nrf2 and NF-κB signaling pathway

The aim of the study was to evaluate the effects of dietary leucine level on growth performance, intestinal antioxidant status and immune response involved in Nrf2 and NF-κB signaling pathway in juvenile golden pompano (Trachinotus ovatus). A total of 450 juvenile golden pompano (9.15 ± 0.04 g) were fed three isonitrogenous diets with graded leucine levels [1.25% (control), 2.77% and 5.84%] for 8 weeks. The results showed that, compared with the control group, the WG was significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05), and the 5.84% dietary leucine group had a tendency to increase. Compared to control group, 5.84% dietary leucine group significantly decreased the moisture and ash contents of whole body (P < 0.05), meanwhile, 2.77% dietary leucine group significantly decreased moisture content of whole body, but significantly improved the whole body crude lipid content (P < 0.05). Compared with the control group, the ALP level was significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05). Inversely, the AST and ALT activities were significantly decreased in fish fed with 2.77% dietary leucine level (P < 0.05). Compared with the control group, GPx, T-AOC, SOD activities in group of 2.77% dietary arginine level were significantly increased (P < 0.05). However, MDA level showed a reverse trend, which was significantly decreased in fish fed with 2.77% dietary leucine level (P < 0.05). 2.77% dietary leucine levels significantly increased the relative expressions of Nrf2, HO-1, Cu/Zn-SOD, Mn-SOD and CAT (P < 0.05). In contrast, the relative expression of Keap1 showed a converse trend. Compared with the control group, the relative expressions of NF-κB, TNF-α and IL1-β were significantly lowered in fish fed with 2.77% of dietary leucine (P < 0.05). Additionally, 2.77% dietary leucine level significantly improved the relative expressions of TGF-β and IL-10 (P < 0.05). The 2.77% dietary leucine level significantly increased the muscular thickness compared with 5.84% dietary leucine level (P < 0.05). Furthermore, compared with the control group, the villus height and goblet cell counts were significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05). These results indicated that the optimum dietary leucine plays an important role in promoting growth, enhancing antioxidant and immunity to maintain the intestinal health status of juvenile golden pompano.

Soybean glycinin impaired immune function and caused inflammation associated with PKC-ζ/NF-κb and mTORC1 signaling in the intestine of juvenile grass carp (Ctenopharyngodon idella)

Glycinin is a major protein and antinutritional factor of soybean. However, how dietary glycinin affect intestinal immune function of fish were largely unknown. In this study, we used juvenile grass carp as a model to investigate the impacts of glycinin on intestinal immune function of fish and involved mechanisms. We set three treatments including control, glycinin and glycinin + glutamine in this trial. For immune components, results revealed that compared with control group, glycinin group had lower acid phosphatase activities in the foregut, midgut and hindgut, lower C3 and C4 content, and lower mRNA abundances of IgM, IgZ, hepcidin, LEAP-2A, LEAP-2B and β-defensin-1 in the midgut and hindgut rather than foregut of grass carp. For pro-inflammatory cytokines and relevant signaling, glycinin elevated mRNA abundances of IL-1β, IL-8, IL-12p35, IL-12p40 and IL-17D in the midgut and IL-1β, IFN-γ2, IL-6, IL-8, IL-12p35, IL-12p40 and IL-17D in the hindgut, and increased protein abundances of PKC-ζ and nuclear NF-κB p65 in the midgut and hindgut in comparison to control. For anti-inflammatory cytokines and relevant signaling, glycinin reduced mRNA abundances of TGF-β1, TGF-β2, IL-4/13B (rather than IL-4/13A), IL-10 and IL-11 in the midgut and hindgut, and reduced p-mTOR (Ser 2448), p-S6K1 (Thr 389) and p-4EBP1 (Thr 37/46) protein abundances in the midgut and hindgut rather than foregut. Co-administration of glutamine with glycinin could partially enhance intestinal function and reduce intestinal inflammation compared with glycinin treatment. Concluded, glycinin decreased intestinal immune components and caused intestinal inflammation associated with PKC-ζ/NF-κB and mTORC1 signaling.

Safety evaluation of four faba bean extracts used as dietary supplements in grass carp culture based on hematological indices, hepatopancreatic function and nutritional condition

Faba bean (Vicia faba, FB) is known to improve the texture of fish meat but retards growth possibly by inducing hemolysis, hepatopancreas damage, and metabolic disorder. In this study, we used ultrasonic processing to isolate four FB extracts (water extract, alcohol extract, proteins and residues) and examined their beneficial and detrimental effects. These extracts were separately mixed with commercial feed and fed to grass carp (Ctenopharyngodon idellus) using whole FB and commercial feed as controls. After fish were fed one of the six experimental diets for 50 d and 100 d, we evaluated the growth and hematological parameters, activities of metabolic enzymes, hepatopancreatic histology and oxidative response, and lipid metabolism. Results showed that both whole FB and FB residues caused growth retardation and hepatopancreas damage (P < 0.05), whereas growth performance was improved in the FB water and alcohol extract groups compared to the whole FB group. Although the FB water extract negatively affected the number and morphological parameters of red blood cells (P < 0.05), the hematological damage was less pronounced than that of the whole FB group. Excessive hepatopancreatic fat accumulation was found in the whole FB, FB alcohol extract and FB residues groups. Moreover, serious hepatopancreas damages were observed in the FB residues group. These results suggest that the beneficial and detrimental components of FB were successfully separated in the four extracts, and the FB water extract would be the best choice for grass carp culture in terms of growth performance and health. The safety evaluation of the four FB extracts would facilitate further application of FB in aquatic feed.

Leucine Improved Growth Performance, Muscle Growth, and Muscle Protein Deposition Through AKT/TOR and AKT/FOXO3a Signaling Pathways in Hybrid Catfish Pelteobagrus vachelli × Leiocassis longirostris

(1) Background: l-leucine (Leu) plays a positive role in regulating protein turnover in skeletal muscle in mammal. However, the molecular mechanism for the effects of Leu on muscle growth and protein deposition is not clearly demonstrated in fish. This study investigated the effects of dietary Leu on growth performance and muscle growth, protein synthesis, and degradation-related signaling pathways of hybrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂). (2) Methods: A total of 630 hybrid catfish (23.19 ± 0.20 g) were fed 6 different experimental diets containing graded levels of Leu at 10.0 (control), 15.0, 20.0, 25.0, 30.0, 35.0, and 40.0 g Leu kg^-1 for 8 weeks. (3) Results: Results showed that dietary Leu increased percent weight gain (PWG), specific growth rate (SGR), FI (feed intake), feed efficiency (FE), protein efficiency ratio (PER), muscle fibers diameter, and muscle fibers density; up-regulated insulin-like growth factor I (IGF-I), insulin-like growth factor I receptor (IGF-IR), proliferating cell nuclear antigen (PCNA), myogenic regulation factors (MyoD, Myf5, MyoG, and Mrf4), and MyHC mRNA levels; increased muscle protein synthesis via regulating the AKT/TOR signaling pathway; and attenuated protein degradation via regulating the AKT/FOXO3a signaling pathway. (4) Conclusions: These results suggest that Leu has potential role to improve muscle growth and protein deposition in fish, which might be due to the regulation of IGF mRNA expression, muscle growth related gene, and protein synthesis and degradation-related signaling pathways. Based on the broken-line model, the Leu requirement of hybrid catfish (23.19-54.55 g) for PWG was estimated to be 28.10 g kg^-1 of the diet (73.04 g kg^-1 of dietary protein). These results will improve our understanding of the mechanisms responsible for muscle growth and protein deposition effects of Leu in fish.

Integrated application of multi-omics provides insights into cold stress responses in pufferfish Takifugu fasciatus

BACKGROUND

T. fasciatus (Takifugu fasciatus) faces the same problem as most warm water fish: the water temperature falls far below the optimal growth temperature in winter, causing a massive death of T. fasciatus and large economic losses. Understanding of the cold-tolerance mechanisms of this species is still limited. Integrated application of multi-omics research can provide a wealth of information to help us improve our understanding of low-temperature tolerance in fish.

RESULTS

To gain a comprehensive and unbiased molecular understanding of cold-tolerance in T. fasciatus, we characterized mRNA-seq and metabolomics of T. fasciatus livers using Illumina HiSeq 2500 and UHPLC-Q-TOF MS. We identified 2544 up-regulated and 2622 down-regulated genes in the liver of T. fasciatus. A total of 40 differential metabolites were identified, including 9 down-regulated and 31 up-regulated metabolites. In combination with previous studies on proteomics, we have established an mRNA-protein-metabolite interaction network. There are 17 DEMs (differentially-expressed metabolites) and 14 DEGs-DEPs (differentially co-expressed genes and proteins) in the interaction network that are mainly involved in fatty acids metabolism, membrane transport, signal transduction, and DNA damage and defense. We then validated a number of genes in the interaction network by qRT-PCR. Additionally, a number of SNPs (single nucleotide polymorphisms) were revealed through the transcriptome data. These results provide key information for further understanding of the molecular mechanisms of T. fasciatus under cold stress.

CONCLUSION

The data generated by integrated application of multi-omics can facilitate our understanding of the molecular mechanisms of fish response to low temperature stress. We have not only identified potential genes and SNPs involved in cold tolerance, but also show that some nutrient metabolites may be added to the diet to help the overwintering of T. fasciatus.

Essential amino acids exhibit variable effects on protein degradation in rainbow trout (Oncorhynchus mykiss) primary myocytes

The functional role of amino acids as regulators of protein degradation was investigated using primary myogenic precursor cell culture as in vitro model of rainbow trout white muscle. Seven-day old myocytes were starved of amino acids for two hours then exposed to media that contained amino acid treatments, during which protein degradation rates were analyzed over five hours by measuring cellular release of ³H-tyrosine. Increasing concentrations of essential amino acids (EAA) reduced protein degradation rates; this effect was dose-dependent within the physiological range found in plasma. Addition of leucine or phenylalanine at 5 mM and 2.5 mM, respectively, decreased rates of protein degradation compared to media without amino acid supplementation, suggesting that these amino acids directly regulate muscle proteolysis. Protein degradation rates were similar in cells exposed to media without EAA and media lacking only leucine, further supporting a role for leucine as a central regulator of protein turnover. Addition of 5 mM lysine or valine to media without amino acids increased protein degradation; this response was attenuated as EAA were added back into media, supporting that a lysine or valine imbalance is costly for muscle protein retention. In summary, there is evidence for amino acids as both positive and negative regulators of protein turnover in rainbow trout muscle. These findings suggest that there may be an optimal plasma amino acid profile that minimizes protein turnover and that this could be achieved through diet formulation.

Time-series transcriptomic analysis of the kelp grouper Epinephelus moara in response to low salinity stress

The Kelp grouper Epinephelus moara is one of the most widely consumed and economically important marine fish in China. The species can tolerate a wide range of salinity, but genomic resources are not available, and the molecular mechanisms underlying adaptation to salinity at the transcriptomic level remain largely unclear. In this study, the transcriptomic responses of the liver of E. moara under low salinity were investigated using the Illumina digital gene expression system. After de novo assembly, 499,356 transcripts were generated and contributed 445,068 unigenes. A total of 14, 19, 33 and 3101 genes were differentially expressed following exposure to low salinity stress for 2, 6, 24 and 48 h, respectively. Only two genes were differentially expressed in all groups. Four genes related to metabolism and ambient salinity adaption were randomly selected to validate the differentially expressed genes (DEGs) by real-time PCR. Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment analysis were used to analyse the functional significance of DEGs, including those responding to salinity through diverse biological processes, cellular components, molecular functions, and pathways associated with metabolic and osmotic responses. This work provides new insight into the response to salinity challenges in E. moara, and the findings expand our knowledge of the molecular basis of metabolic regulation mechanisms in this species. Additionally, the transcriptional data provide a valuable resource for future molecular and genetic studies on E. moara.

Dietary leucine modulates growth performance, Nrf2 antioxidant signaling pathway and immune response of juvenile blunt snout bream (Megalobrama amblycephala)

The present study assessed the effects of dietary leucine on growth performance, antioxidant status and immunity in juvenile blunt snout bream. Fish were fed six practical diets of graded leucine levels ranging from 0.90% to 2.94% of dry basis for 8 weeks. Trail results showed that compared to control group (0.90%), 1.72% dietary leucine level significantly improved final weight (FW), weight gain rate (WG) and specific growth rate (SGR), and significantly lowered feed conversion ratio (FCR). Based on WG and SGR, the optimal dietary leucine level was obtained at 1.40% and 1.56%, respectively. Whole body crude lipid and protein contents were improved with increasing dietary leucine up to 2.14% and thereafter showed a downward trend, while whole body moisture content showed a converse trend. No significant change was found in whole body ash content. 1.72% dietary leucine level significantly improved the antioxidant capacity of fish by regulating the plasma superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, total antioxidant capacity (T-AOC) activity, catalase (CAT) activity, aspartate aminotransferase (AST) activities and malondialdehyde (MDA) content, furthermore, 1.72% dietary leucine level also significantly improved the antioxidant genes expressions of associated with Nrf2 signaling pathway by regulating heme oxygenase-1 (HO-1), GPx, copperezinc superoxide dismutase (Cu/Zn-SOD), manganese superoxide dismutase (Mn-SOD), 2.14% dietary leucine levels also significantly improved glutathione transferase (GST) mRNA level. Dietary leucine levels significantly affected plasma immunity parameters such as the contents of plasma complement component 3 (C3), immunoglobulin M (IgM) and lowered the hepatopancreas genes expressions of pro-inflammatory factor by regulating interleukin 1β (IL-1β), interleukin 8 (IL-8) and tumour necrosis factor-α (TNF-α) mRNA levels. The present study indicated that optimal dietary leucine level plays an important role in improving growth, enhancing antioxidant and immune status to maintain the health in juvenile blunt snout bream.