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Abstract Background Bone morphogenetic proteins (BMPs) are part of the transforming growth factor beta (TGF-β) superfamily and play crucial roles in bone development, as well as in the formation and maintenance of various organs. Triplophysa dalaica, a small loach fish that primarily inhabits relatively high elevations and cooler water bodies, was the focus of this study. Understanding the function of BMP genes during the morphogenesis of T. dalaica helps to clarify the mechanisms of its evolution and serves as a reference for the study of BMP genes in other bony fishes. The data for the T. dalaica transcriptome and genome used in this investigation were derived from the outcomes of our laboratory sequencing. Results This study identified a total of 26 BMP genes, all of which, except for BMP1, possess similar TGF-β structural domains. We conducted an analysis of these 26 BMP genes, examining their physicochemical properties, subcellular localization, phylogenetic relationships, covariance within and among species, chromosomal localization, gene structure, conserved motifs, conserved structural domains, and expression patterns. Our findings indicated that three BMP genes were associated with unstable proteins, while 11 BMP genes were located within the extracellular matrix. Furthermore, some BMP genes were duplicated, with the majority being enriched in the GO:0008083 pathway, which is related to growth factor activity. It was hypothesized that genes within the BMP1/3/11/15 subgroup (Group I) play a significant role in the growth and development of T. dalaica. By analyzing the expression patterns of proteins in nine tissues (gonad, kidney, gill, spleen, brain, liver, fin, heart, and muscle), we found that BMP genes play diverse regulatory roles during different stages of growth and development and exhibit characteristics of division of labor. Conclusions This study contributes to a deeper understanding of BMP gene family member expression patterns in high-altitude, high-salinity environments and provides valuable insights for future research on the BMP gene family in bony fishes.

Cadmium (Cd) pollution is considered a pressing challenge to eco-environment and public health worldwide. Although it has been well-documented that Cd exhibits various adverse effects on aquatic animals, it is still largely unknown whether and how Cd at environmentally relevant concentrations affects iron metabolism. Here, we studied the effects of environmental Cd exposure (5 and 50 μg/L) on iron homeostasis and possible mechanisms in common carp. The data revealed that Cd elevated serum iron, transferrin saturation and iron deposition in livers and spleens, leading to the disruption of systemic iron homeostasis. Mechanistic investigations substantiated that Cd drove hemolysis by compromising the osmotic fragility and inducing defective morphology of erythrocytes. Cd concurrently exacerbated hepatic inflammatory responses, resulting in the activation of IL6-Stat3 signaling and subsequent hepcidin transcription. Notably, Cd elicited ferroptosis through increased iron burden and oxidative stress in livers. Taken together, our findings provide evidence and mechanistic insight that environmental Cd exposure could undermine iron homeostasis via erythrotoxicity and hepatotoxicity. Further investigation and ecological risk assessment of Cd and other pollutants on metabolism-related effects is warranted, especially under the realistic exposure scenarios.

Membrane fatty acid desaturase (FADS)‐like superfamily proteins (FADSs) are essential for the synthesis of unsaturated fatty acids (UFAs). Recently, studies on FADS in fishes have mostly focused on marine species, and a comprehensive analysis of the FADS superfamily, including the FADS, stearoyl‐CoA desaturase (SCD), and sphingolipid delta 4‐desaturase (DEGS) families, in freshwater economic fishes is urgently required. To this end, we conducted a thorough analysis of the number, gene/protein structure, chromosomal location, gene linkage map, phylogeny, and expression of the FADS superfamily. We identified 156 FADSs genes in the genome of 27 representative species. Notably, FADS1 and SCD5 were lost in most freshwater fish and other teleosts. All FADSs proteins contain 4 transmembrane helices and 2–3 amphipathic α‐helices. FADSs in the same family are often linked on the same chromosome; moreover, FADS and SCD or DEGS are frequently collocated on the same chromosome. In addition, FADS, SCD, and DEGS family proteins share similar evolutionary patterns. Interestingly, FADS6, as a member of the FADS family, exhibits a similar gene structure and chromosome location to that of SCD family members, which may be the transitional form of FADS and SCD. This study shed light on the type, structure, and phylogenetic relationship of FADSs in freshwater fishes, offering a new perspective into the functional mechanism analysis of FADSs.

The subfamily Gobioninae is one of the most diverse fish groups within Cyprinidae. Their taxonomy and phylogenetic relationships are not completely resolved. In this study, the complete mitochondrial genomes (mitogenome) of four Gobioninae species (Microphysogobio elongatus, Microphysogobio chinssuensis, Gobio rivuloides and Rhinogobio nasutus) were sequenced and compared. The mitogenomes of four species ranges from 16603 bp to 16609 bp in length, consisting of 13 protein-coding genes (PCGs), 22 tRNA genes, two rRNA genes, and a control region. Most PCGs had significant codon usage bias. Except for the tRNASer (GCT), all the nucleotide substitutions of tRNA loops higher than the stems could fold into a stable secondary structure. The nucleotide compositions of Gobioninae mitogenome were biased toward A/T, and NAD4 was subjected to low purification selection and had a faster evolution rate among 13 PCGs. Bayesian inference and maximum likelihood phylogenetic analyses showed the consistent results. The four sequenced species clustered together with their congener species. However, more samples and mitogenome data are needed to untangle the phylogenetic relationships among genera Microphysogobio, Romanogobio, Hugobio, Biwia and Platysmacheilus.

Among the polyphenolic compounds commonly found in green tea, (-)-epigallocatechin-3-gallate (EGCG) is known to have various functions, including the promotion of antioxidant and myofiber growth in mammals. However, the effect of EGCG on common carp (Cyprinus carpio L.) remains poorly understood. To evaluate the role of EGCG on juvenile common carp, 255 fish (initial weight 17.33 ± 0.34 g) were fed with five experimental diets containing 0, 0.05, 0.25, 0.5, and 1 g/kg EGCG. The results showed that diet supplementation with 0.05–0.5 g/kg EGCG supplementation significantly enhanced the specific growth rate (SGR) and reduced the feed conversion ratio (FCR). Weight gain rate (WGR) was significantly enhanced in the 0.25 and 0.5 g/kg EGCG groups. As for antioxidants, 0.25–1 g/kg EGCG significantly reduced protein carbonyl (PC) content and upregulated superoxide dismutase (sod) gene expression in the muscle. As for muscle nutritional composition, 0.05–0.5 g/kg EGCG increased total amino acid (TAA) and flavor amino acid (FAA) contents, likely via the rapamycin (mTOR) signaling pathway. Muscle n-3 polyunsaturated fatty acids (n-3 PUFA) content was increased with 0.5 g/kg EGCG, presumably owing to the upregulation of fatty acyl elongase 5 (elovl5), long-chain fatty acyl-CoA synthetase 6 (acsl6), and peroxisome proliferator-actiated receptor α (pparα). Dietary EGCG (0.05–1 g/kg) significantly increased muscle hardness and chewiness, accompanied by an increase in myofiber density. EGCG supplementation (0.25–1 g/kg) increased the pH value and reduced lactate contents in the muscle. However, muscle crude lipid and hydroxyproline contents significantly decreased with 1 g/kg EGCG. Overall, quadratic regression analysis of WGR, SGR, TAA, and FAA showed that optimal EGCG (0.46–0.52 g/kg) dietary supplementation improved the growth and nutritional composition of juvenile common carp.

Long-term consumption of high-carbohydrate feed may adversely affect intestinal health of fish; however, the underlying roles remain ambiguous. This study examined the effects of varying carbohydrate levels on the intestinal flora of common carp and assessed how microbial metabolites influence intestinal health. Two hundred seventy common carps were chosen and distributed randomly into three groups that fed diets containing starch at levels of 15% (low-carbohydrate diet [LCD]), 28% (medium-carbohydrate diet [MCD]), and 45% (high-carbohydrate diet [HCD]) for 60 days. A significant increase in final body weight, weight gain rate, and specific growth rate within the MCD group, while feed conversion ratio exhibited a decrease in comparison to the other groups (p

In the present study, we conducted a 10-week culture experiment to investigate the effects of taurine on the growth performance, antioxidant properties, and muscle quality of the common carp fed an oxidized lipid diet. There were five experimental groups with three replicates each. Based on the fresh fish oil group (FO), equal amounts of oxidized fish oil (with a thiobarbituric acid-reactive substances value of 49.57 ± 2.34 mg/kg) and 0 g/kg (OFO), 4 g/kg (OT4), 8 g/kg (OT8), and 12 g/kg (OT12) taurine were added to the diet, while the same composition ratio was maintained by changing the microcrystalline cellulose content. Compared to the FO group, the feed conversion ratio, weight gain rate, muscle crude lipid, and n-3/n-6 polyunsaturated fatty acids (PUFA) ratio were significantly lower in the group OFO (P

Acheilognathus barbatulus is distributed in Yangtze River, Yellow River and Pearl River systems in China. Genome data can help to understand the phylogenetic relationships of A. barbatulus, but its complete mitochondrial genome has not been published. We determined the complete mitochondrial genome structure and characteristics of this species and constructed a comprehensive phylogenetic tree, based on mitochondrial genome data of several species of Acheilognathus, Rhodeus and Pseudorasbora parva. The complete length of the mitochondrial genome of A. barbatulus is 16726 bp. The genome is a covalently closed double-stranded circular molecule containing 13 protein-coding genes, two ribosomal RNAs, 22 transfer RNAs, a D-loop and a light strand replication initiation region. The base composition of the complete mitochondrial genome is A (29.33%) > T (27.6%) > C (26.12%) > G (16.95%), showing a strong AT preference and anti-G bias. All 13 PCGs have different degrees of codon preference, except for cytochrome c oxidase 1, which uses GTG as the start codon. All the PCGs use ATG as the start codon and the stop codon is dominated by TAG. The encoded amino acids Leu and Ser exist in two types, whereas the rest are all present as one type, except for tRNASer (GCT), which lacks the D-arm and has an incomplete secondary structure, all other tRNAs can be folded to form a typical cloverleaf secondary structure. Based on the 13 PCG tandems, the Maximum Likelihood and Bayesian trees were constructed, based on the concatenated sequence of 13 PCGs for the genera Acheilognathus and Rhodeus, with Pseudorasbora parva as the outgroup. Acheilognathus barbatulus, Acheilognathus tonkinensis and Acheilognathus cf. macropterus were clustered together and the most closely related. The results of this study enrich the mitochondrial genomic data of Acheilognathus and provide molecular and genetic base information for species conservation, molecular identification and species evolution of Acheilognathinae.

Abstract Background The solute carrier 4 (SLC4) gene family is involved in a variety of physiological processes in organisms and is essential for maintaining acid-base balance in the body. The slc4 genes have been extensively studied in mammals, and they play important roles in intracellular and extracellular pH regulation and in the secretion and uptake of HCO3 − and other ions (Na+ and Cl−) between transepithelial cells in different tissues. This study identified and characterized the entire slc4 gene family of Triplophysa dalaica. Results Fifteen slc4 genes were identified in the whole genome of Triplophysa dalaica in this study, including five copies of Na+-independent Cl−/HCO3 − transporters, eight members of Na+-dependent HCO3 − transporters, and two genes coding Na+-coupled borate transporters. The chromosomal location information, isoelectric points, and molecular weights of the 15 slc4 genes were analyzed. The results for gene structure, domain analysis, and phylogenetic relationships of this gene family showed that the slc4 genes (except for slc4a9, which is missing in teleosts) are significantly expanded in teleosts compared to higher vertebrates. This phenomenon suggests that the slc4 gene family played an important role in the transition from aquatic to terrestrial animals. RT-PCR results showed that different slc4 genes showed diversified expression patterns in the tissues of T. dalaica. For osmotic pressure regulating organs, slc4a1b, slc4a4b, slc4a7, and slc4a11a were highly expressed in gills. In the kidney, slc4a1a, slc4a3, and slc4a10b were highly expressed, suggesting that the slc4 genes play a specific role in the salinity adaptation of T. dalaica. Our study has deciphered the biological roles of the slc4 genes in maintaining ionic and acid-base homeostasis in teleost fishes and provides a foundation for future exploration of the highly differentiated gene family in Triplophysa. Conclusions The results are relevant for the breeding of alkali-tolerant varieties in saline-alkali areas for aquaculture. Our findings have important implications for the adaptation process of freshwater species to saline-alkali water.

Abstract Biological denitrification is a crucial process in the nitrogen biogeochemical cycle, and Thermus has been reported to be a significant heterotrophic denitrifier in terrestrial geothermal environments. However, neither the denitrification potential nor the evolutionary history of denitrification genes in the genus Thermus or phylum Deinococcota is well understood. Here, we performed a comparative analysis of 23 Thermus genomes and identified denitrification genes in 15 Thermus strains. We confirmed that Thermus harbors an incomplete denitrification pathway as none of the strains contain the nosZ gene. Ancestral character state reconstructions and phylogenetic analyses showed that narG, nirS, and norB genes were acquired by the last common ancestor of Thermales and were inherited vertically. In contrast, nirK of Thermales was acquired via two distinct horizontal gene transfers from Proteobacteria to the genus Caldithermus and from an unknown donor to the common ancestor of all known Thermus species except Thermus filiformis. This study expands our understanding of the genomic potential for incomplete denitrification in Thermus, revealing a largely vertical evolutionary history of the denitrification pathway in the Thermaceae, and supporting the important role for Thermus as an important heterotrophic denitrifier in geothermal environments.

This study sought to examine the role of bile acids in the regulation of glucose and lipid metabolism, intestinal flora, and growth in high-fat diet-fed common carp (Cyprinus carpio L.). Fish (6.34±0.07 g) were fed for 56 days with three different diets, the control diet (CO, 5.4% lipid), high-fat diet (HF, 11% lipid), and high-fat diet with 60 mg/kg bile acids (BAs, 11% lipid). The results showed that high-fat diets resulted in poor growth performance and increased triglyceride (TG) in serum and the liver. The addition of bile acids significantly alleviated the adverse effects of a high-fat diet. The mRNA expression results indicated that bile acids may improve lipid metabolism through the enhancement of the peroxisome proliferator-activated receptor (PPARa). The expression of gluconeogenesis-related phosphoenolpyruvate carboxykinase (PEPCK) mRNA was inhibited, while fibroblast growth factor 19 (FGF19) was significantly higher. Bile acids reshaped the intestinal microflora community, with the level of Bacteroidetes increasing. The correlation analysis indicated that Patescibacteria, Dependentiae, Myxococcota, and Planctomycetota in the gut are associated with genes involved in glucose and lipid metabolism. These results indicated that bile acids could ameliorate the negative effects of high-fat diets on common carp.

A 56-day feeding trial was conducted to investigate the effects of genistein on growth, lipid metabolism, antioxidant capacity, and immunity of common carp fed with high-carbohydrate or high-fat diets. Five diets were used to feed fish: control diet (5% fat; CO), high-fat diet (11% fat; HF), high-carbohydrate diet (45% carbohydrate; HC), and HF or HC diet with 500 mg/kg genistein (FG or CG). Results showed that final body weight (FW) and specific growth rate (SGR) were significantly reduced, but the supplementation with genistein resulted in higher values of FW and SGR than the HF or HC group. Both high carbohydrate and high fat belong to high-energy diets, which may promote lipid deposition. Genistein obviously decreased liver triglyceride (TG) content and alleviated hepatic fat vacuolation in the HF and HC groups. The expression of lipid metabolism genes (cpt-1 and atgl) was markedly higher in the FG group than in the HF group. The lipid synthesis-related genes (fas, acc, and pparγ) were elevated in high-energy diets but recovered to the control level or reduced after genistein treatments. With respect to fatty acid transporter genes, fatp increased in the FG group, and cd36 increased in the CG group. Furthermore, the antioxidant and immune indexes, such as total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-PX), superoxide dismutase (SOD), acid phosphatase (ACP), and lysozyme (LZM) activities, were decreased, while malonate aldehyde (MDA) content, activities of alanine aminotransferase (ALT), and aspartate aminotransferase (AST) were enhanced in the HF and HC groups. The antioxidant and immunity values could be ameliorated by treatment with genistein. Moreover, the transcript levels of antioxidant-related genes (cat, gr, and nrf2) in the liver and anti-inflammatory factors (tgf-β and il-10) and lyz in the head kidney tissue were promoted, although the expression levels of proinflammatory factors (tnf-α and il-6) declined in the genistein supplementation group, which confirmed the antioxidant and immune-enhancing effects of genistein. Therefore, 500 mg/kg genistein could ameliorate the negative effects of high-energy diets on immunity.

In order to investigate the roles of adiponectin in glucose and lipid metabolism in common carp, the tissue distribution of adiponectin and its receptor genes in common carp were firstly detected in this study, and then the effects of high-carbohydrate (45%) and high-lipid (11%) diets on their expressions were studied in the feeding trial. The results showed that adipoqa and adipoqb mRNA levels were highest in the red muscle, followed by the heart and white muscle. Adiponectin receptor genes were widely expressed in all tested tissues. Two subtypes of adiponectin receptor 1 genes (adipor1a and adipor1b) were expressed at the highest level in the brain, while adipor2 mRNA was highly expressed in the heart and red muscle. The high-carbohydrate diet significantly up-regulated adipoqa and adipoqb mRNA level in the heart of common carp, while the high-lipid diet significantly promoted adipoqa mRNA expression in the red muscle and heart, compared to the control diet. For adiponectin receptor gene expression, a high-carbohydrate diet up-regulated adipor2 mRNA level in the hepatopancreas, while a high-lipid diet significantly promoted adipor1a, adipor1b and adipor2 mRNA expression in the red muscle and hepatopancreas. The results showed that both high-carbohydrate and high-lipid diets could induce adiponectin genes expression in common carp, and AdipoRs expression was more likely to be increased by the high-lipid diet than the high-carbohydrate diet. This study suggested that adiponectin and its receptors were involved in the metabolic regulation of fish under high dietary carbohydrate and lipid levels.

This experiment investigated the effects of dietary sodium acetate (SA) on the growth performance, intestinal health, and carbohydrate metabolism of juvenile Cyprinus carpio L. Four experimental diets were evaluated, including diets supplemented with 0.5 %, 1.0 % and 1.5 % SA and a control diet without supplementation. Triplicate repetitions (n = 30) of common carp (initial weight of 17.24 ± 0.40 g) per group were fed the respective diets for 8 weeks. Dietary SA significantly improved final weight, specific growth rate (SGR), weight gain (WG) and condition factor (CF) and a lower feed conversion ratio (FCR) compared to control group (P 0.05). For intestinal health, dietary SA significantly promoted digestive enzyme activities, including amylase, lipase and protease, and increased villus length and muscle thickness. With respect to carbohydrate metabolism, dietary SA significantly decreased blood glucose levels and hepatopancreas glycogen content, downregulated sglt1 and gult2 gene expression in the intestine (P

Homatula are peculiar taxa in China, distributed in the Yellow River, Yangtze River, Pearl River, Lancang River drainage and Red River. At present, 17 valid species have been already reported in China.Homatula guanheensis sp. nov., a new species, is described from the Guanhe River of the HanJiang River drainage (a tributary of the Yangtze River), Xixia County, Henan province, China. The species can be distinguished from its congeners by a combination of molecular divergence in the Cytochrome oxidase I (CO I) and Cytochrome b (Cyt b) genes and morphological characters, including a shallower body with a uniform depth, differences in the widths of vertical brown bars on the body, body scale distribution, length of the dorsal adipose crest of the caudal peduncle, and the form of the intestine.

This study explored the protective effect of broken tea on growth, antioxidant capacity, nutritional composition and lipid metabolism in fish fed a high-fat (HF) diet. A total of 450 Cyprinus carpio (18.79 ± 3.16 g) were divided into five groups and fed for 8 weeks: the control diet group (C), HF diet group (HF), and the HF diet plus 1 %, 2 % and 3 % broken Xinyang Maojian tea (BTMaojian) groups (HF+1%BT, HF+2 %BT and HF+3 %BT). We found that the weight gain rate (WGR) of carp was increased significantly in the HF+ 3 %BT group compared with the control group (P

This study was conducted to evaluate the effects of a dietary earthworm meal mixture (earthworm meal: EM and wormcast: WC) for replacing fish meal (FM) on growth performance, antioxidant capacity, lipid metabolism, and intestinal health of common carp (Cyprinus carpio L.). FM was used as the protein source in the control diet (D1), while 30% FM protein was replaced with an EM and WC mixture in the experimental diets, and the specific mixing ratio was as follows: D2 (15.4% EM), D3 (15.1% EM and 1.8% WC), D4 (14.8% EM and 3.7% WC), and D5 (14.5% EM and 5.8% WC). The growth performance was significantly decreased in the D4 and D5 groups compared with the D1 group, while the condition factor was highest in the D2 group (P

The distribution of fat among both invertebrate and vertebrate groups is heterogeneous. Studies have shown that fatty acid‐binding proteins (FABPs), which mainly bind and transport fatty acids, play important roles in the regulation of fat storage and distribution. However, the systematic and genome‐wide investigation of FABP genes in organisms with a heterogeneous fat distribution remains in its infancy. The availability of the complete genomes of Caenorhabditis elegans, Callorhinchus milii, and other organisms with a heterogeneous fat distribution allowed us to systematically investigate the gene structure and phylogeny of FABP genes across a wide range of phyla. In this study, we analyzed the number, structure, chromosomal location, and phylogeny of FABP genes in 18 organisms from C. elegans to Homo sapiens. A total of 12 types of FABP genes were identified in the 18 species, and no single organism exhibited all 12 fatty acid‐binding genes (FABPs). The absence of a specific FABP gene in tissue may be related to the absence of fat storage in the corresponding tissue. The genomic loci of the FABP genes were diverse, and their gene structures varied. The results of the phylogenetic analysis and the observation of conserved gene synthesis of FABP family genes/proteins suggest that all FABP genes may have evolved from a common ancestor through tandem duplication. This study not only lays a strong theoretical foundation for the study of fat deposition in different organisms, but also provides a new perspective regarding metabolic disease prevention and control and the improvement of agricultural product quality.

Genistein exhibits anti-diabetic and anti-lipogenic effects in mammals, however, there are rare reports on the effects of genistein on glucose and lipid metabolism in fish. This study explored the regulation role of genistein on glucose and lipid metabolism of common carp. After oral gavage with genistein (20 mg/kg body weight), the content of genistein in serum was the highest at 4 h and rapidly returned to basal values at 48 h. The blood glucose (GLU) concentrations were decreased at 24 h after gavage with genistein. The total cholesterol (TC) level was significantly down-regulated by genistein except for 24 h (P

Omega-3 fatty acids have a positive effect on the muscle textural firmness of fish, while the intrinsic mechanism is poorly understood. To investigate the potential mechanism of textural modification caused by dietary docosahexaenoic acid ( DHA) in common carp (Cyprinus carpio L.), three plant-derived diets with varying DHA levels (0%, 0.5%, 1%, D1–D3) were prepared to feed juveniles (initial weight 15.27 ± 0.77 g) for 8 weeks, and the muscular texture, fibers density, and transcriptome were analyzed. The results showed that the growth performance, muscular DHA content, fibers density, and texture of the fish fed diets D2 and D3 were significantly ameliorated compared with the fish fed diet D1. The muscular transcriptome profiles indicated that the up-regulated genes of fish fed dietary DHA mainly in response to muscle proliferation, as well as the FoxO pathway, were significantly enriched in the D2 and D3 groups. Consistent with this, the Quantitative Real-Time PCR (qRT-PCR ) assays indicated that the expression of myogenic regulatory factors (myog, myod, mrf4, mrf5) was up-regulated in the high-DHA groups. Additionally, the expression of foxo1 (inhibitor of myofiber development) mRNA was down-regulated, while its negative regulatory pathway (MAPK and PI3K) was activated in the D2 and D3 groups. The results suggested that the DHA supplementation is beneficial to modifying the muscular textural firmness of common carp fed plant-derived diets, which could be attributed to the inhibition of FoxO1 pathways.

Recently, the concept of precision nutrition has emerged in aquaculture, and there is increasing discussion on this topic. Some researchers have defined precision nutrition as precision feeding, which means that the nutrient contents of feed should meet the requirements for an animal’s optimal production performance and achieve minimum fodder waste at the same time. In practice, precision nutrition should include a comprehensive survey of the animal’s genetic background, living habits, metabolic characteristics, water ecological environment and other factors. Precision nutritional regulation covers every level, from genes, cells, and tissues to the whole organism. Through interacting with genes, nutrients activate or inhibit signalling pathways/networks within cells, which regulate gene expression and protein synthesis and subsequently affect the composition, content and deposition sites of carbohydrates, lipids, proteins and trace elements. Therefore, we propose that precision nutritional intervention needs to be carried out from the perspectives of ‘precision feeding’, ‘precision metabolism’, ‘precision output’ and ‘precision support’ simultaneously. This review intends to elaborate the concept evolution, theoretical system, and composition of the technical system, together with other aspects of precision nutritional regulation. This knowledge will provide a theoretical reference for the sustainable development of the aquaculture industry and the harvesting of quality products.

In order to study the effects of replacement of soybean meal (SM) with defatted black soldier fly larvae meal (BSFLM) in grass carp production practice, juvenile grass carps with initial body weight of (10.10 ± 0.28) g were selected for subsequent tests. Five isolipidic (49.1–50.3 g kg−1) and isonitrogen (321.4–327.8 g kg-1) experimental diets were formulated by replacing 0 % (SM), 25% (BSFLM25), 50% (BSFLM50), 75% (BSFLM75) and 100% (BSFLM100) of SM with BSFLM, respectively. After 56 days of feeding, the changes of growth performance, body composition, serum biochemical indexes, antioxidant capacity, digestive enzyme activity, intestinal and liver tissue structure, and intestinal microbiota of grass carp were detected. The results showed that there were no significant differences in growth, feed efficiency and muscle proximate compositions among the treatment groups. The BSFLM100 group had significantly higher TG content than the other groups. Catalase activity was significantly increased in BSFLM25 and BSFLM50 groups compared with that in the SM group. The activities of amylase and lipase in BSFLM50, BSFLM75, and BSFLM100 groups were lower than the control group. Compared with the SM group, the intestinal villi length and the thickness of the intestinal wall of BSFLM75 and BSFLM100 groups were decreased. Gut microbiota analysis showed no significant changes in the operational taxonomic unit (OTU) diversity and richness indices among treatments. However, the abundance of Aeromonas and Shewanella decreased significantly after substitution with BSFLM. These results show that there was no negative effect on growth performance and improved the antioxidant capacity of grass carp when dietary SM complete replacement by BSFLM. However, when the replacement level exceeds 50 %, intestinal histomorphology may be damaged.

The present study assessed the effects of different ratios of dietary linolenic acid (LNA) to linoleic acid (LA) from vegetable oils on growth performance, ovarian steroidogenesis, plasma sex steroid hormone, and tissue fatty acids accumulation in juvenile common carp (Cyprinus carpio). With fish oil, peanut oil, and perilla oil as lipid source, five experimental diets containing 32% crude protein and 8% crude lipid were formulated with LNA/LA ratios of 0.97 (control diet), 0.02, 0.46, 1.09, and 1.53, respectively. The diets were assigned to 15 tanks (50 L) of carp, and the fish (8.10 ± 0.11 g, n = 25) were manually fed to apparent satiation twice daily in triplicate groups for 16 weeks. The survival rate and feed conversion ratio were not significantly different among treatments (P > 0.05). Results demonstrated that fish fed diet with LNA/LA ratio of 1.09 exhibited the highest body weight gain, and was no significantly different with fish fed control diet. Fish fed diet with LNA/LA ratio of 1.53 showed the highest gonadosomatic index (P < 0.05). The expression of StAR, 17β-HSD and Cyp19a1a in ovary were up-regulated, and plasma E2 increased with increasing of dietary LNA/LA ratios (P < 0.05). Fish fed diet with LNA/LA ratio of 0.02 showed the lowest plasma E2 and T. The expression of Fads6-a and Elovl5-a in liver expressed higher in fish fed with dietary LNA/LA ratio of 1.09. LNA, LA, Docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) contents in liver were significantly affected by dietary LNA/LA ratios. LNA content in liver and LNA and ARA content in ovary increased with the increasing of dietary LNA/LA ratios. Results of this study indicated that dietary LNA/LA ratios alter both growth and ovarian development, and provided evidence that balanced LNA/LA ratio was beneficial for growth and ovarian development of juvenile common carp.

Orexins are neuropeptides involved in energy homeostasis. In fish, the function of orexin-A in glucose metabolism is less reported. The present study aims to identify the potential role of orexin-A in the glucose absorption and metabolism in common carp. The full length of orexin cDNA was cloned using RT-PCR and RACE method. The prepro-orexin cDNA was 513 bp containing an open reading frame of 474 bp and encoded 157 amino acids which including 47 amino acids of orexin-A and 28 amino acids of orexin-B. The tissue distribution results showed that orexin was expressed in multiple tissues, especially with high-level expression in hypothalamus. The exogenous orexin-A protein was chemical synthesized. Intraperitoneal injection of orexin-A alleviated the increase of plasma glucose level at 1 h and 2 h after OGTT (Oral glucose tolerance test). Orexin-A also decreased glucose uptake activity and the expression of sglt1 and glut2 mRNA in intestine. However, orexin-A significantly increased the mRNA expression of glut2 in liver and glut4 in muscle. Moreover, the gluconeogenesis-related gene fbpase mRNA was significantly down-regulated, while glycolysis-related genes gk and hk were significantly up-regulated after treatment with orexin-A in vivo and vitro. These results implied that hyperglycemia could be alleviated in common carp after the injection of orexin-A and suggest a role of this peptide as a plasma glucose regulator by inhibition glucose absorption in intestine, promotion glucose transport to liver and muscle. Furthermore, hepatic gluconeogenesis was inhibited. Taken together, this study helped to understand the characterization of prepro-orexin and the function of orexin-A in fish glucose homeostasis.

Our objective is to study the low metabolic utilization of dietary carbohydrates in fish. The regulation of key enzymes involved in glucose and lipid metabolism in the common carp (Cyprinus carpio L.), known to be relatively tolerant to dietary carbohydrates, were assessed. We performed intraperitoneal (i.p.) administration of insulin and glucagon to common carp and also subjected common carp primary hepatocytes to insulin or glucagon. The results showed that insulin administration induced hypoglycaemia through up-regulation of the expression of the glycolysis genes glucokinase (GK) and hexose kinase (HK), coupled with increased gene expression of fatty acid synthase (FAS), acetyl-CoA carboxylase-1 (ACC-1), sterol-regulator element-binding protein-1 (SREBP-1). Insulin also limited the expression of the gluconeogenesis genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), coupled with decreased gene expression of lipoprotein lipase (LPL) and carnitine palmitoyl transferase I (CPT-1). However, glucagon had the opposite effect. The results showed that glucagon induced hyperglycemia with increased expression of PEPCK and G6Pase and increased lipolytic capacity as indicated by lower mRNA levels of SREBP-1. Glucagon (i.p.) significantly increased the activity of PEPCK and LPL in hepatopancreas. In addition, the mRNA expression of HK showed an up-regulated trend and the mRNA expression of PEPCK and G6Pase showed a down-regulated trend in the group of glucose (i.p.). This study demonstrates that insulin and glucagon possess the intrinsic ability to regulate hepatic energy metabolism in common carp, the regulation of which seems to be similar to that of the mammals at least at the molecular level.

Since discovery, glucagon biology has remained enigmatic. Studies have shown that glucagon may have physiological effects beyond glucose regulation by binding to its receptor (Gcgr). The potential roles of glucagon and its receptor in the crosstalk between glucose metabolism and immune function of fish remain to be investigated. In the present study, we sequenced and characterized gcgra and gcgrb in grass carp. Phylogenetic analysis showed that they were highly homologous with their counterparts in fish. The gcgra and gcgrb mRNAs were ubiquitously expressed in all the tissues examined. The gcgra mRNA was highly expressed in the liver and gcgrb was mainly expressed in the liver and brain regions of grass carp. Furthermore, the results of oral glucose tolerance test (OGTT) showed that the expression levels of the two receptors were significantly increased at 12 h after treatment. In the hepatocytes, insulin inhibited gcgra and gcgrb mRNA expressions at 3−12 h and 6−12 h, respectively. While glucagon promoted their expressions at 3−12 h and 3 h, respectively. Intraperitoneal injection of lipopolysaccharide (LPS) increased hepatic gcgra mRNA level at 6 h post treatment, and up-regulated gcgrb mRNA abundance in the liver at 24 h. In response to polyinosinic polycytidylic acid [poly (I:C)] stimuli, however, gcgra and gcgrb mRNA levels were decreased. These results suggested that glucagon receptors were affected by bacterial-like and virus-like infection beyond their roles in the glucose metabolism of grass carp.

A three-month feeding trial was conducted to investigate the effects of faba bean (Vicia faba L.) on growth performance, intramuscular collagen content, muscle cellularity and fillet texture of Yellow River carp, Cyprinus carpio haematopterus. Carps with an initial weight 500 ± 20 g were randomly divided into two treatments: commercial feed group (CFG) and faba bean group (FBG). Compared to CFG, the results indicated that carps fed with faba bean had poor growth performance, higher intramuscular collagen content, smaller fiber diameter and wider intermyofibrillar space. However, the fiber density was not influenced (P > 0.05). The faba bean components showed lower crude protein and amino acid imbalance, especially, the deficiency in the sulfuric amino acid. The raw-fillet and cooked-fillet texture of FBG were both significantly greater than that of CFG (P 0.05). In summary, faba bean could improve the fillet quality for Yellow River carp. These findings would contribute to define the optimal nutritional conditions of pond culture to improve the flesh quality of Cyprinus carpio haematopterus.

Abstract Background Glucose plays a key role as an energy source in most mammals, but its importance in fish appears to be limited that so far seemed to belong to diabetic humans only. Several laboratories worldwide have made important efforts in order to better understand this strange phenotype observed in fish. However, the mechanism of carbohydrate/glucose metabolism is astonishingly complex. Why basal glycaemia is different between fish and mammals and how carbohydrate metabolism is different amongst organisms is largely uncharted territory. The utilization of comparative systems biology with model vertebrates to explore fish metabolism has become an essential approach to unravelling hidden in vivo mechanisms. Results In this study, we first built a database containing 791, 593, 523, 666 and 698 carbohydrate/glucose metabolic genes from the genomes of Danio rerio, Xenopus tropicalis, Gallus gallus, Mus musculus and Homo sapiens, respectively, and most of these genes in our database are predicted to encode specific enzymes that play roles in defined reactions; over 57% of these genes are related to human type 2 diabetes. Then, we systematically compared these genes and found that more than 70% of the carbohydrate/glucose metabolic genes are conserved in the five species. Interestingly, there are 4 zebrafish-specific genes (si:ch211-167b20.8, CABZ01043017.1, socs9 and eif4e1c) and 1 human-specific gene (CALML6) that may alter glucose utilization in their corresponding species. Interestingly, these 5 genes are all carbohydrate regulation factors, but the enzymes themselves are involved in insulin regulation pathways. Lastly, in order to facilitate the use of our data sets, we constructed a glucose metabolism database platform (http://101.200.43.1:10000/). Conclusions This study provides the first systematic genomic insights into carbohydrate/glucose metabolism. After exhaustive analysis, we found that most metabolic genes are conserved in vertebrates. This work may resolve some of the complexities of carbohydrate/glucose metabolic heterogeneity amongst different vertebrates and may provide a reference for the treatment of diabetes and for applications in the aquaculture industry.

The Peptide Transporter 1 (PepT1) plays an important role in animal protein nutrition. This is a low-affinity/high-capacity, stereoselective transmembrane transporter that mediates the uptake of a fraction of dietary amino acids in their di- and tripeptide forms. PepT1 is highly expressed in the intestines of vertebrates and the current studies examining PepT1 function have concentrated mostly on mammals and less emphasis has been placed on protein nutrition in fish. In the gastrointestinal track, amino acids are absorbed more efficiently in the form of small peptides than as free amino acids suggesting a potential role of PepT1 in the optimization of amino acid absorption which is relevant for fish nutrition. Therefore, this review focused on the physiological characteristics, structures, tissue distribution and expression of PepT1 transcripts and regulation of PepT1 protein in fish.

Apelin, a kind of active polypeptide, has many biological functions, such as promoting food intake, enhancing immunity, and regulating energy balance. In mammals, studies have indicated that apelin is involved in regulating food intake. However, there are relatively few studies about the regulatory effect of apelin on fish feeding, and the specific mechanism is not clear. Therefore, the purpose of this study was to preliminarily investigate the regulatory effects of apelin on key genes of feeding and growth in common carp (Cyprinus Carpio L.) through in vitro and in vivo experiments. In the present study, after incubation with different concentrations of Pyr-apelin-13 (0, 10, 100, and 1000 nM) in hypothalamic fragments, the expressions of Neuropeptide Y (NPY) and Agouti related peptide (AgRP) mRNA were significantly up-regulated at 12 and 3 h, respectively, and the significant down-regulation of Cocaine and amphetamine-related transcript (CART) mRNA expression was observed at 1 and 3 h. In vivo, after Pyr-apelin-13 oral administration (0, 1, 10, and 100 pmol/g), the orexin mRNA level in the hypothalamus of common carp was significantly increased at 1, 6, and 12 h, while CART/(Proopiomelanocortin) POMC mRNA levels in the hypothalamus of common carp were significantly down-regulated. Following incubation with different concentrations of Pyr-apelin-13 (0, 10, 100, and 1000 nM) in primary hepatocytes, GHR (Growth hormone receptor), IGF2 (Insulin-like growth factor 2), IGFBP2 (Insulin like growth factor binding protein 2), and IGFBP3 (Insulin like growth factor binding protein 3) mRNA levels were significantly increased at 3 h. In vivo, the levels of IGF1 (Insulin-like growth factor 1), IGF2, IGFBP2 (Insulin like growth factor binding protein 2), and IGFBP3 mRNA were significantly increased after the oral administration of Pyr-apelin-13 in the hepatopancreas, in a time and dose-dependent manner. These results support the hypothesis that Pyr-apelin-13 might regulate the feeding and growth of common carp through mediating the expressions of appetite- and growth-related genes. Overall, apelin, which is an orexigenic peptide, improves food intake and is involved in the growth of common carp.