This exploratory study examined associations between dietary exogenous bile acids (BAs) and growth, hepatic glucose metabolism, intestinal and liver health status, and fillet quality on rice field eel (Monopterus albus) fed high-carbohydrate diets (HC, 35% alpha-starch). Fish were fed a control diet (15% alpha-starch), or HC diets supplemented with 0.05 and 0.1% BAs for 8-week. The HC diet was associated with hyperglycemia, hepatic glycogen accumulation, and signs of impairments in intestinal and liver health. Dietary BAs supplementation was associated with higher growth performance and dose-dependent effects on hepatic glucose metabolism (0.1% BA treatment significantly lower serum glucose and hepatic glycogen content). Positive changes were observed in intestinal parameters, including digestive enzyme activity, antioxidant capacity, mucosal morphology, and genes expression related to physical barrier function and inflammation. BA supplementation was also associated with lower liver oxidative stress markers and functional indicators. Fillet texture parameters showed positive associations. Notably, whole-body composition and serum triglycerides showed no significant differences among groups. In conclusion, dietary BA supplementation was associated with multiple physiological changes in this fish fed a HC diet, including higher growth, dose-dependent associations with glucose metabolism, and positively changes in intestinal and liver health indicators and fillet quality. However, these associations were selective rather than systemic, and the underlying mechanisms remain to be fully elucidated. Given the exploratory nature of this study and limited replication (n = 3), these findings provide a preliminary basis for future hypothesis-driven research into the functional roles of BAs in fish growth, carbohydrate metabolism, and health.

A pathogenic bacterium strain, LBK2, was isolated from giant spiny frog (Quasipaa spinosa) tadpoles infected with perforation disease in this study. Pathogenic strain LBK2, a Gram-negative bacterium with a certain degree of infectivity, was demonstrated to cause anorexia, lethargy, epidermal necrosis, and abdominal perforation in tadpoles in artificial infection experiments. The identification results of 16S rDNA gene sequencing showed that pathogenic strain LBK2 was identified as Pseudomonas sp. Virulence gene identification displayed that strain LBK2 carried three virulence genes: aer, epr, and fla. Finally, the antibiotic susceptibility testing of 11 antibiotics suggested that strain LBK2 was highly sensitive to nine antibiotics, including chloramphenicol, enrofloxacin, and rifampicin, but was resistant to erythromycin, sulfamethoxazole/trimethoprim, and low-concentration trichloroisocyanuric acid. This study determined the pathogenicity of Pseudomonas sp. to giant spiny frog tadpoles based on histopathological analysis and virulence factor carriage, and the drug susceptibility testing further provided a scientific basis for the selection of drugs in the prevention and treatment of abdominal perforation disease in giant spiny frog tadpoles.

To comprehensively investigate effects of dietary L-carnitine (LC) on growth performance, lipid metabolism, oxidative stress, mitochondrial function and endoplasmic reticulum (ER) stress in farmed fish fed highcarbohydrate-diets (HCD), 960 rice field eels (17.09 +/- 0.14 g) were chosen and randomly assigned to 16 cages. These fish were fed a control diet (15% alpha-starch, CON), a high-carbohydrate-diet (35% alpha-starch, HCD), a HCD supplemented with 1.2%o LC (HC/LLC), and a HCD supplemented with 2.4%o LC (HC/HLC). Results of 8week feeding trial showed that HCD increased liver lipid content, induced liver dysfunction, oxidative stress and endoplasmic reticulum (ER) stress, but did not affect growth performance. Dietary LC supplementation increased significantly weight gain rate and specific growth rate and decreased liver lipid content. Concurrently, LC reduced the activity of alanine transaminase enzyme in the serum, improved liver's antioxidant capacity, thereby mitigating liver damage. Dietary LC positively regulated the expression of genes related to oxidative stress, such as Kelch-like ECH-associated protein 1, nuclear factor erythroid 2-related factor 2, catalase and superoxide dismutase in fish. Furthermore, LC supplementation upregulated expression of genes related to the mitochondrial function, such as cardiolipin synthase 1 and lysocardiolipin acyltransferase 1 (cardiolipin metabolism), peroxisome proliferator-activated receptor gamma coactivator 1 alpha, peroxisome proliferatoractivated receptor alpha and carnitine palmitoyltransferase 1 (mitochondrial beta-oxidation) in fish. Intriguingly, administering LC-fortified diets resulted in downregulation of ER stress-related gene expression, such as glucose regulated protein 78, inositol-requiring enzyme 1 and activating transcription factor 6 in fish. For the first time, this study reports that the incorporation of LC into HCD facilitates lipid metabolism of fish through concurrent enhancement of mitochondrial function, reduction of oxidative stress, and alleviation of ER stress.

This study explored effects of yeast culture (YC) and complex probiotics (CP) on the growth performance, liver-intestinal health and fillet quality of rice field eel (Monopterus albus). 1200 healthy fish with initial weight (23.04 +/- 0.04) g were selected and randomly divided into 5 groups (4 replies per group): control group, 0.3 % YC group, 0.6 % YC group, 0.3 % CP group and 0.6 % CP group. Results of 56-d experiment showed that postbiotics could significantly increase final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR) and reduced feed conversion rate (FCR) (P < 0.05). Dietary postbiotics reduced the total lipid content in liver (P < 0.05), increased protein deposition in whole body and muscle (P < 0.05). Dietary postbiotics also improved liver and intestinal antioxidant ability (total superoxide dismutase, catalase, glutathione peroxidase, glutathione) (P < 0.05), immune function (serum acid phosphatase, alkaline phosphatase and liver lysozyme activities) (P < 0.05), and intestinal digestive ability (alpha-amylase, trypsin) (P < 0.05). Meanwhile, dietary postbiotics significantly enhanced intestinal villi height and mucosal barrier integrity (P < 0.05). High-throughput sequencing revealed that, intestinal microbial probiotics (Firmicutes and Bacteroidetes) abundance increased and pathogenic (Proteobacteria) abundance decreased in the postbiotic-treating group (P < 0.05). It is worth noting that dietary postbiotics could improve muscle quality (P < 0.05), reduce muscle fibers area and diameter (P < 0.05), and promote protein deposition (P < 0.05). In summary, dietary postbiotics can show beneficial effects on growth, liver and intestinal health, and muscle quality in this fish.

The species diversity of freshwater mussels in the upper Yangtze River has been seriously underestimated, and human-induced disturbances have severely threatened the survival of local bivalve species. In this study, we describe a new freshwater mussel species, Cristaria wangyucheni Z.-G. Chen &amp; Y.-T. Dai, sp. nov., from the Jialing River Basin in the upper Yangtze River, Sichuan, China, based on comparative morphology and molecular phylogeny. Phylogenetic analyses of COI and 28S rRNA gene fragments revealed that C. wangyucheni sp. nov. is a sister to the other species of Cristaria. The pairwise uncorrected COI p-distance analysis demonstrated genetic distances ranging from 10.10% (between this species and C. truncata) to 13.17% (between this species and C. “beirensis”). Morphologically, C. wangyucheni sp. nov. can be distinguished from its congeners by its medium-sized shell, which ranges from an elongated triangle to an irregular rectangle. This discovery broadens our understanding of interspecific shell morphological variation within the genus Cristaria.

Emodin supplementation could relieve the adverse impacts induced by a high plant-protein diet on intestinal health and growth performance of fish, while its application in Pengze crucian carp (Carassius auratus var. Pengze) is lacking. Pengze crucian carp, an omnivorous fish, belongs to the freshwater Cyprinidae family. In this study, Pengze crucian carp were fed with a normal fishmeal diet (18% fishmeal, FM), a high plant-protein diet (4% fishmeal, HP), and four different emodin supplementation diets (HP diet supplemented with 25, 50, 75, and 100 mg kg−1 emodin); the feeding trial lasted 8 weeks. Compared with the FM group, the HP diet dramatically inhibited the growth performance of carp, while an appropriate addition of emodin could restore its growth performance. Emodin could improve carp morphology in terms of a higher value of the hepatosomatic index (HSI), the viserosomatic index (VSI), and the condition factor (CF), and increase the crude protein content concurrent with a lower crude lipid content in body compared with HP and FM groups. The HP diet induced the oxidative stress of carp, whereas emodin supplementation enhanced antioxidant parameters in serum and intestinal tissues together with a remarkable reduction of malondialdehyde content, thereby improving antioxidant status. The antioxidant property of emodin triggered the keap1-nrf2 signal pathway and then induced the overexpression of antioxidant genes (cuznsod, cat, and gpx) in intestinal tissue. Additionally, emodin attenuated the intestinal inflammation induced by the HP diet by suppressing the expression of pro-inflammatory-related factors (tlr4, myd88, tnf-α, il-1β, and ifn-γ) and upregulating anti-inflammatory-related factors (tlr2, tgf-β, and il-10), followed by an improvement of the intestinal barrier function. Moreover, emodin supplementation could induce the transcriptional level of intestinal alkaline phosphatase (iap) through the pparγ-klf4 signal pathway and enhance IAP activity ultimately. In summary, a suitable amount of emodin can elevate the growth performance and improve the intestinal health of Pengze crucian carp fed a high plant-protein diet.

Carbohydrate is a common energy substance in aquaculture feed. Most studies show that the ability of fish to use carbohydrate is limited. This experiment aims to explore the effects of different carbohydrate levels on the growth mechanism of medium-sized grass carp medium-sized (Ctenopharyngodon idellus). 450 medium-sized grass carp with an initial weight of 45 +/- 0.12 g were randomly divided into five groups, with three replicate cages per group and 30 fish per replicate. They were fed five different levels of carbohydrate diet: Group A (28.84 %), Group B (33.74 %), Group C (38.64 %), Group D (43.54 %), and Group E (48.44 %), with adjusted inert filler (cellulose) levels to ensure that each group's diet was isonitrogenous for 8 weeks.The results shows that as carbohydrate levels increase, the relative expression levels of weight gain rate (WGR), specific growth rate (SGR), feed coefficient (FCR), protein conversion efficiency (PER), and growth hormone (gh) genes in the pituitary gland, as well as growth hormone receptor (ghr) and insulin-like growth factor 1/2 (igf-1,2) genes in the liver, first increased and then decreased; The gene expression of somatostatin receptors 1,2,3,5 (sstr1,2,3,5) in the pituitary gland and somatostatin precursors (pss1,2,3) in the hypothalamus first decrease and then increase. At the metabolic level, the visceral body index (VSL), liver body index (HSI), intraperitoneal fat index (IPF), and liver crude fat content of grass carp increase, while serum triglycerides (TG), total cholesterol (T-CHO), and low-density lipoprotein cholesterol (LDL-C) significantly increase; The relative expression levels of genes involved in glycolysis and lipid metabolism (pfk, acc, fas, hsl, cpt-1) in the liver gradually increase. Overall, the carbohydrate tolerance range of medium-sized grass carp is 34.47 %-40.41 %, and excessive tolerance can seriously affect their growth and liver health; Somatostatin (SS) in fish can regulate carbohydrate and glucose lipid metabolism, and its specific molecular mechanisms and signaling pathways need further in-depth research.

With the increasing prevalence of high-fat diets (HFD) in aquaculture practices, the detrimental effects of HFD on farmed fish have garnered significant attention. Creatine has emerged as a promising green feed additive for aquaculture species; however, its potential role in mitigating the negative impacts of HFD remains poorly understood. To address this knowledge gap, the present study was designed to investigate the protective effects of dietary creatine supplementation on HFD-induced hepatic lipid metabolism disorders and muscle quality deterioration in juvenile grass carp (Ctenopharyngodon idella). Three experimental diets were formulated: a control diet (5.20% lipid, control), a HFD (8.11% lipid, HFD), and a HFD supplemented with 2% creatine (HFD + creatine). Juvenile grass carp (initial weight: 4.12 ± 0.02 g) were randomly allocated into nine 300-L indoor tanks and fed the experimental diets for 8 weeks. The key findings of this study revealed that (1) Dietary creatine supplementation significantly ameliorated the adverse effects of HFD on growth performance and feed utilization efficiency in juvenile grass carp. (2) Creatine supplementation improved muscle quality parameters in juvenile grass carp. (3) Dietary creatine attenuated HFD-induced hepatic lipid accumulation through enhanced fatty acid β-oxidation, which was mediated by mfn2-dependent mitochondrial fusion. Notably, this study elucidates a novel molecular mechanism whereby creatine activates mitochondrial fusion through the binding of pparα transcription factor to specific sites on the mitofusin 2 (Mfn2) gene promoter. To our knowledge, this is the first comprehensive investigation from a multi-organ/tissue perspective combined with mitochondrial dynamics analysis, providing valuable insights for developing effective nutritional strategies to counteract HFD-induced adverse effects in farmed fish through creatine supplementation.

Dietary lipid intake can dramatically alter the host microbiota and bile acids (BAs) metabolism. To explore the effect of endogenous BAs and intestinal microorganisms in the adaptive mechanism of grass carp (Ctenopharyngodon idellus) to different dietary lipid levels, triplicate groups of grass carp were fed three isonitrogenous diets with low (2 %), normal (6 %) and high (10 %) lipid levels and named group E2, E6 and E10, respectively. Results showed that a 6 % dietary lipid level was optimal for achieving the maximum growth performance and maintaining the liver health state of grass carp. The levels of glucose (GLU), high-density lipoprotein cholesterol (HDL-C), and malonaldehyde (MDA), along with the activities of acetyl-coA carboxylase (ACC), carnitine palmitoyl-transferase 1 (CPT1), fatty acid binding protein (FABP) and fatty acid transport protein (FATP) were significantly lower in fish that fed diet E2 than those that fed diet E6 (P < 0.05). The activities of acid phosphatase (ACP), alkaline phosphatase (AKP), glutamic oxalacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) were significantly higher in fish fed diet E10 than in those fed diet E6 (P < 0.05). While there were no notable differences in the activities of lipid metabolism-related enzymes between fish fed diets E6 and E10 (P > 0.05), fish fed diet E10 exhibited a greater presence of vacuoles and lipid buildup in the liver compared to fish on diet E6. In the gallbladder, the levels of multiple BAs in fish that were given diet E2 were considerably lower than those in fish that received diet E6. However, the intestinal contents of fish that were given diet E2 showed significantly higher levels of multiple BAs than those on diet E6, while fish on diet E10 exhibited the opposite pattern. Additionally, fish fed diet E6 showed a higher presence of Fusobacterium and Cetobacterium, while the ratio of Proteobacteria decreased. Furthermore, multiple BAs were positively correlated with lactic acid bacteria-related genera from Firmicutes and a significant negative correlation with dietary lipid levels. These findings indicated that microbial-mediated bile acid hepatoenteric circulation plays an important role in the adaptive mechanism of fish to different dietary lipid levels, and it is expected to be an important intervention target for lipid metabolism disorders of grass carp.

The aim of this study was to investigate effects of dietary metformin supplementation on growth performance, liver function, and glucose metabolism of rice field eel (Monopterus albus) fed high carbohydrate diets (HCDs). Four isonitrogenous and isolipid diets were formulated, different in 15% α-starch (LC), 35% α-starch (HC), and 35% α-starch supplemented with 0.25% (HCM0.25) and 0.5% metformin (HCM0.5), respectively. After 8 weeks, the results showed that HCDs did not affect growth performance, but reduced the activities of amylase and trypsin, and damaged liver function together with the increase of hepatic glycogen content. HCM0.25 did not affect whereas HCM0.5 damaged the growth performance. Activities of amylase in HCM0.25 group and trypsin in both HCM0.25 and HCM0.50 groups were increased. While HCM0.25 lowered serum AST and ALT activities, HCM0.5 showed an increase. HCM0.25 caused a reduction in vacuoles size and a increase in nuclei number, whereas HCM0.5 failed to induce similar effects. The liver glycogen content was reduced by both HCM0.25 and HCM0.5 whereas the muscle glycogen content remained stable. Both HCM0.25 and HCM0.5 enhanced glycolysis–related enzymatic activities (PFK, PK) in liver, while reducing gluconeogenesis (FBPase). Similarly, both treatments upregulated gene expression of pk in liver, while downregulated g6pase, fbpase and pepck. Moreover, HCM0.25 and HCM0.5 increased PFK, G6Pase, FBPase and PEPCK activity in muscle, with HCM0.25 further upregulating gene expressions of hk, pfk, g6pase and pepck. Both treatments downregulated the gene expression of g6pd in muscle, whereas only HCM0.25 upregulated ampkα1, tbc1d1 and glut4. In summary, dietary 0.25% metformin improved liver function, reduced liver glycogen content, and regulated glucose metabolism and AMPKα-TBC1D1-GLUT4 pathway. However, 0.50% metformin did not demonstrate positive effects and even had adverse effects on growth performance.

Abstract Compound plant extracts (CPE) are beneficial for aquatic animals on growth performance and antioxidant capacity. A 56‐day experiment was conducted to investigate its positive effect on rice field eel. The fish were fed a commercial diet and supplementing CPE (mainly containing eucommia polysaccharides, reducing sugar) at 0, 0.8, 1.6, 2.4, and 3.2 g/kg. Results showed that dietary CPE significantly increased weight gain and specific growth rate (p < 0.05). Liver lipid content in 1.6 and 3.2 g/kg groups was significantly lower than in 0.8 and 2.4 g/kg groups (p < 0.05). Muscle lipid content in 0.8, 2.4, and 3.2 g/kg CPE groups was significantly lower than in control (p < 0.05). Meanwhile, intestinal digestive enzymatic activities in the 3.2 g/kg CPE group were the highest in comparison to all other groups (p < 0.05). Dietary CPE enhanced the antioxidant activities of serum and intestine (p < 0.05). Compared with the control, intestinal fold thickness in CPE groups was significantly increased (p < 0.05). Furthermore, dietary CPE reduced the degree of liver steatosis and the number of lipid droplet vacuoles. This study indicated that dietary CPE was beneficial to growth performance, antioxidant capacity, liver, and intestinal histology. Supplementation with 1.6–3.2 g/kg CPE is optimal for this eel species.

AMP-activated protein kinase-alpha 1 (AMPK alpha 1) plays a vital role in glucose and lipid metabolism. Five isonitrogenous and isolipid diets with starch levels (15%, 20%, 25%, 30% and 35%) were formulated to study the modulation of AMPK alpha 1 in hepatic lipid deposition induced by high gelatinized starch diet in rice field eel (Monopterus albus) (initial body weight, 30.00 +/- 0.10 g) and the growth trial lasted for 8 weeks. The results showed that dietary gelatinized starch did not affect the growth performance of rice filed eel compared with S15 group. High gelatinized starch could induce AMPK alpha 1 expression and glucose catabolism, and inhibit hepatic glycogen synthesis without effecting glucose content. Dietary >= 30% gelatinized starch began to dramatically suppress gluconeogenesis and promote the lipid synthesis, followed by a higher triglyceride (TG) and hepatic crude lipid. Dietary 20-30% gelatinized starch induced phosphorylation of AMPK alpha compared to 15% gelatinized starch diet, whereas 35% starch dramatically suppressed AMPK alpha phosphorylation together with unnormal increase in phosphorylation of forkhead box O1 A (FOXO1A) and acetyl-CoA carboxylase (ACC), TG content compared to 30% starch. In short, high gelatinized starch could induce AMPK alpha 1 expression and promoted systemic metabolism, whereas dietary >= 25% gelatinized starch initially suppressed AMPK alpha 1 activation and caused abnormal lipid deposition in liver of rice field eel.

To assess the dietary arginine requirement of Monopterus albus (21 ± 0.03 g), we compared six diets containing different arginine levels (2.03%, 2.58%, 3.16%, 3.63%, 4.24%, and 4.88%). The results revealed that dietary arginine content had a significant effect on weight gain (WG), specific growth rate (SGR), IL-1β, IL-10, lysozyme, and complement C3 activity in Monopterus albus ( p < 0.05 ). The WG and SGR increased with increasing dietary arginine levels, and the regression analysis found that the optimum dietary arginine level for growth of rice field eel was 4.28–4.35% of the dry diet. However, the C3 and LZM activities peaked in the 2.58% arginine diet group ( p < 0.05 ). The dietary arginine level had no significant effect on the viscerosomatic index, hepatosomatic index, condition factor, survival rate, nitric oxide, total nitric oxide synthase, insulin, growth hormone, trypsin, lipase, or amylase activities ( p > 0.05 ). Arginine can significantly promote Monopterus albus growth; however, the immunity of Monopterus albus decreases as the arginine level exceeds 2.58%. A comprehensive assessment of growth and immunity recommends the optimum arginine level for Monopterus albus was 3.16–3.63% of the dry diet, corresponding to 6.58–7.70% of the dietary protein.

To understand the effects of vitamin A on lipid deposition in rice field eels, integrated liver transcriptome and metabolome were conducted and the changes in the genes and metabolites were assessed. Three groups of rice field eel were fed with 0, 200, and 16,000 IU/kg vitamin A supplementations in their diets for 70 days. The total lipid content in the whole body of the rice field eels was significantly increased with the vitamin A supplementations (p < 0.05). Comparative transcriptome analysis revealed 14 pathways and 46 differentially expressed genes involved in lipid metabolism. Sphingolipid metabolism, glycerolipid metabolism, primary bile acid biosynthesis and steroid hormone biosynthesis were significantly enriched pathways. In these pathways, three differential genes phospholipid phosphatase 1a (PLPP1a), phospholipid phosphatase 2b (PLPP2b), cytochrome P450 21a2 (CYP21a2) were consistent with the change trend of lipid content, and the other three differential genes aldo-keto reductase family 1 member D1 (AKR1D1), uridine diphosphate glucuronic acid transferase 1a1 (UGT1a1), cytochrome P450 1a (CYP1a) were opposite. Metabolomic analysis revealed that primary bile acid biosynthesis, sphingolipid metabolism, steroid hormone biosynthesis and biosynthesis of unsaturated fatty acids were all critical for rice field eel metabolic changes in response to vitamin A. Six important differential metabolites (eicosapentaenoic acid, sphinganine, 11-beta-hydroxyprogesterone, hydroxyeicosatetraenoic acid, cholic acid, and glycochenodeoxycholate) were identified and have provided new insights into how vitamin A regulates lipid deposition. Integrated transcriptome and metabolome analyses revealed that primary bile acid biosynthesis was the only remarkably enriched pathway in both the transcriptome and metabolome while that sphingosine was the main metabolite. Based on the above results, we have concluded that vitamin A promotes lipid deposition in the rice field eel through the primary bile acid synthesis pathway, and lipid deposits are widely stored in cell membranes, mainly in the form of sphingosine. These results will provide reference data to help improve our understanding of how vitamin A regulates lipid metabolism.

The purpose of this trial was to study the positive effects of bile acids (BAs) on growth performance and intestinal health of rice field eel fed with high-lipid diets (HLDs). Rice field eels (initial weight 17.00 ± 0.10 g) were divided into four groups, each group containing four repetitions and feeding with different isonitrogenous diet: control diet containing 7% lipid content, HLDs containing the lipid content increased to 13%, HLDs supplementing with 0.025% BAs and 0.05% BAs, respectively. After 8 weeks, compared control group, the fish fed HLDs had no significant effect on weight gain rate and specific growth rate (P>0.05), but increased the lipid deposition in tissues and intestinal lipase activity, and damaged to intestinal oxidative stress, inflammatory response, physical barrier, and structural integrity (P<0.05). Dietary BAs significantly increased weight gain rate and specific growth rate in fish fed with HL diets (P<0.05) and reduced feed conversation rate (P<0.05). Further, the eels fed with BAs reduced the total lipid content in liver, muscle, and whole body (P<0.05). Dietary BAs decreased the activity of intestinal lipase (P<0.05). Meanwhile, BAs supplemented in HLDs improved intestinal antioxidant capacity through increasing the activities of T-SOD (total superoxide dismutase), GSH-PX (glutathione peroxidase), CAT (catalase), T-AOC (total antioxidant capacity), whereas reducing MDA (malondialdehyde) content (P<0.05). Moreover, dietary BAs regulated the mRNA expression related to inflammatory response, oxidative stress, and physical barrier in intestine, such as tnf-α, il-8, tlr-8, il-10, nrf2, keap1, claudin12, and claudin15 (P<0.05). Dietary BAs supplementation also enhanced the intestinal structural integrity characterized by increased fold height and lamina propria width (P<0.05). This study showed that dietary BAs supplemented in HLDs (13% lipid) could increase the growth performance of rice field eel, reduce lipid deposition in tissues and whole body, and enhance intestinal health.

A 10-week long feeding trial was run to determine the effects of inosine monophosphate (IMP) as functional nutrient on growth, feed utilization, haemato-immunological characteristics, and in-testinal morphology of juvenile T. putitora. Casein and fishmeal based semi-purified basal diet (control) was formulated to contain 40 % protein and 10 % lipid. Four levels of IMP nucleotide viz., 0.05 %, 0.1 %, 0.2 % and 0.4 % were added to the basal diet for diet groups IMP-0.05, IMP -0.1, IMP-0.2 and IMP-0.4, respectively. Each diet was assigned randomly to triplicate groups of fish occupying an initial average weight of 9.1 +/- 0.02 g. The results indicated that dietary IMP significantly enhanced the growth performance of fish and fish fed IMP-0.05 and IMP-0.1 diets showed significantly highest values. Compared to the control, IMP-0.05 diet group showed significantly lower feed conversion ratio, while protein efficiency ratio (PER) was significantly higher in fish fed IMP-0.05 and IMP-0.1 diet groups followed by IMP-0.2 diet group. Control and IMP-0.4 groups showed significantly lower PER. Higher IMP included group (IMP-0.4) showed significantly lower feed intake value. Again, the whole-body lipid content was significantly influenced by dietary IMP inclusion among major whole-body nutrients. Significantly reduced plasma glucose, bilirubin, and alanine aminotransferase level accounted for in IMP supplemented units compared to the control. IMP supplementation also significantly improved total immuno-globulin and hematocrit content. Supplementation of IMP significantly increased and decreased peroxidase and catalase activity, respectively. Fish fed 0.05-0.15 % IMP supplemented diets showed significant improvement in fold height (hF), enterocyte height (hE) and microvillus height (hMV) of anterior intestine compared to the control. In posterior intestine, similar supplementation level of IMP (0.05-0.15 %) showed significant improvement in hE and hMV, while hF showed numerically higher values except in fish fed IMP-0.05 diet group. Based on the current experimental conditions, a dietary IMP of 0.05 % resulted in improved outcomes in the majority of the fish growth and health performance indicators. However, quadratic regression analysis of all the significantly influenced fish performance parameters disclosed that the optimal level of dietary IMP was 0.17 % and this is also consistent with the majority of fish growth and health performance measures.

The phenomenon of intestinal dysfunction is widely observed in white shrimp (Litopenaeus vannamei) culture, and β-1,3-glucan has been confirmed to be beneficial in intestinal health with a lack understanding of its underlying mechanism. Proteobacteria, Firmicutes, and Actinobacteria served as the predominant phyla inhabiting the intestine of white shrimp, whilst a significant variation in their proportion was recorded in shrimp fed with basal and β-1,3-glucan supplementation diets in this study. Dietary supplementation of β-1,3-glucan could dramatically increase the microbial diversity and affect microbial composition, concurrent with a notable reduction in the ratio of opportunistic pathogen Aeromonas, gram-negative microbes, from Gammaproteobacteria compared to the basal diet group. The benefits for microbial diversity and composition by β-1,3-glucan improved the homeostasis of intestinal microbiota through the increase of specialists' number and inhibition of microbial competition caused by Aeromonas in ecological networks; afterward, the inhibition of Aeromonas by β-1,3-glucan diet dramatically suppressed microbial metabolism related to lipopolysaccharide biosynthesis, followed by a conspicuous decrease in the intestinal inflammatory response. The improvement of intestinal health referred to the elevation in intestinal immune and antioxidant capacity, ultimately contributing to the growth of shrimp fed β-1,3-glucan. These results suggested that β-1,3-glucan supplementation improved the intestinal health of white shrimp through the modulation of intestinal microbiota homeostasis, the suppression of intestinal inflammatory response, and the elevation of immune and antioxidant capacity, and subsequently promoted the growth of white shrimp.

Glucose transporter 4(GLUT4)directly promoted the absorption of glucose by cells and plays a vital role in glucose metabolism.In mammals,GLUT4 is mainly expressed in skeletal muscle and adipose tissue,and had been systematically research on the mechanism of regulation of the GLUT4 transport function.It has been reported that GLUT4 is involved in signal pathways related to carbohydrate metabolism,including phosphatidylinositol 3-kinase/protein kinase B(PI3K/Akt),AMP-activated protein kinase(AMPK),and protein kinase C(PKC).Since the GLUT4 is found in fish,it had been confirmed that GLUT4 in fish had high homolo-gy with mammals,with different structure and transport mode from those of mammals.The effect of insulin-dependent pathway on glucose absorption in fish was preliminarily explored.AMPK,as an important factor in the non-insulin-dependent glucose transport pathway,had been shown to affect the glucose absorption process in fish.However,PKC signaling pathway was not involved in GLUT4-mediated glucose metabolism in fish.Exploring the mechanism of glucose metabolism in fish has always been the hotspot of fish nutrition.This review would focus on the above three signal pathways by which regulate the transportation of glucose,summarizes the research on GLUT4 in fish,and provides the corresponding theoretical basis for further research of the mechanism of glucose metabolism in fish.

The aim of this trial was to investigate the effects of apple polyphenols (AP) and taurine (TA) on the growth performance, tissue morphology, and lipid and glucose metabolism in rice field eel fed diets with high oxidized fish oil (OFO). A 10-week feeding experiment was conducted using juveniles (initial body weight 16.66 ± 0.02 g) fed five different diets. Three diets were formulated with various levels of OFO at 9.5, 600, and 800 meq·kg−1 and named as Control, POV600, and POV800 diet, respectively. The other two diets were POV600 and POV800 supplemented with 0.5% AP and 0.2% TA, respectively. Compared to the Control group, only the eels fed POV800 exhibited an increase in weight gain and specific growth rate along with a reduction in feed conversion ratio. AP and TA did not affect growth performance; juveniles fed AP, however, showed a decrease in liver weight. Both POV600 and POV800 decreased nuclei number and increased vacuoles size in the liver. POV800 damaged the intestinal structure integrity and reduced goblet cells number. AP repaired the liver damage on nuclei number and vacuoles size in fish fed with POV600 diet, while TA mitigated intestinal histopathological damage on intact structure and goblet cells number. The mRNA expression level of liver ampkα in fish fed AP was upregulated, while dietary TA upregulated the mRNA expression levels of liver ampkα and accα. In the muscle, POV600 downregulated mRNA expression levels of accα, cpt1, and lipin, whereas POV800 upregulated mRNA expression levels of accα, pparα, and lipin. Dietary AP and TA could counteract the effects of POV600 and POV800 diet on muscle lipid metabolism. Both POV600 and POV800 diets upregulated mRNA expression levels of liver pck1 and gsk3α. AP and TA both downregulated mRNA expression level of liver pck1, while only TA downregulated the expression of liver gsk3α. AP increased the mRNA expression level of gsk3α in muscle. In summary, inclusion of AP and TA did not affect growth performance but showed a potential to alleviate liver or intestinal damages induced by a high OFO diet. Dietary AP and TA were also found to regulate mRNA expression of genes related to lipid and glucose metabolism.

[目的]试验研究了7种不同糖源(葡萄糖、蔗糖、玉米淀粉、小麦淀粉、粘米粉、木薯淀粉、马铃薯淀粉)饲料的表观消化率及对黄鳝[初始质量为(21.08±0.43)g]生长性能的影响.[方法]试验设置7个处理组,每组4个重复,每个重复20尾黄鳝.试验饲料配制,使用秘鲁鱼粉、大豆浓缩蛋白和酪蛋白为蛋白源,鱼油和豆油(1:1)为脂肪源,Y2O3为外源指示剂,分别添加30％的不同糖源.试验饲料饲喂黄鳝为60 d,饲喂4周后采用虹吸法收集成型粪便用于测定.[结果]小麦粉与粘米粉组黄鳝取得较好的生长性能,木薯淀粉和马铃薯淀粉生长性能其次,但优于蔗糖和葡萄糖组,葡萄糖组生长性能最差.粗蛋白和粗脂肪的表观消化率,小麦粉与粘米粉组较高,木薯淀粉和马铃薯淀粉组次之,葡萄糖和蔗糖组最低.各组间胃消化酶活力无影响,肝胰脏和肠道的消化酶活力小麦粉和粘米粉组较强.葡萄糖和玉米淀粉组黄鳝肝糖原积累量低于其他5组.黄鳝摄食不同糖源饲料血糖峰值出现时间不同,多数在餐后3～6 h,其中玉米淀粉、粘米粉和马铃薯组出现在3 h,蔗糖、小麦、木薯淀粉组出现在6h,蔗糖组在摄食后3～6h血糖浓度都维持在较高水平;葡萄糖组在1h出现峰值,一直维持在最低水平,木薯淀粉和马铃薯淀粉饲料黄鳝血糖水平长期维持较高水平.[结论]7种饲料糖源中,小麦粉与粘米粉较适宜作为黄鳝饲料糖源.