High-carbohydrate aquafeeds can induce metabolic disorders and growth inhibition in fish. This study aimed to investigate the beneficial effects of sodium acetate supplementation to a high-carbohydrate diet on grass carp (Ctenopharyngodon idella) and the related molecular mechanisms. Three isonitrogenous and isolipidic diets, including MC (27.5

Compared to mammals, fish exhibit poor carbohydrate utilization. Thus, exploring exogenous additives to promote efficient carbohydrate utilization in fish holds significant promise. In mammals, dietary supplementation with tea polysaccharides (TPS) has been associated with alleviating metabolic syndrome and inhibiting intestinal enzyme activities. However, limited research has focused on the effects of TPS on metabolic syndrome in fish. In this study, grass carp were fed three experimental diets (control; high-carbohydrate, HG; high-carbohydrate supplemented with 0.05% TPS, HG+TPS) for 8 weeks to investigate the effects of TPS supplementation on growth performance and carbohydrate utilization in fish fed a high-carbohydrate diet. Following the feeding trial, the HG+TPS group exhibited a significantly higher specific growth rate compared with the HG group. TPS supplementation inhibited exogenous glucose uptake in fish fed a high-carbohydrate diet by downregulating intestinal alpha-glucosidase activity and hepatic glut2 gene expression. In addition, TPS supplementation increased hepatic pk expression to stimulate glycolysis compared with the HG group. Furthermore, the hepatic glycogen content of fish fed the HG+TPS diet was increased by decreasing the pygl gene expression compared to fish fed with the HG diet. Therefore, TPS supplementation alleviated glucose stress induced by high carbohydrate intake by inhibiting intestinal glucose absorption, enhancing hepatic glycogen accumulation, and promoting the glycolysis process. These results provide evidence of the potential application of TPS as an antihyperglycemic additive in aquatic feeds.

In mammals, glucose-dependent insulinotropic polypeptide (GIP) exerts a potent hypoglycemic effect, whereas its role in fish remains controversial. In this study, synthetic grass carp GIP was administered via intraperitoneal injection, and its effects were evaluated over 24 h. GIP significantly elevated blood glucose levels at 0.5 h post-injection compared to the saline control. This hyperglycemia was accompanied by increased hepatic expression of the gluconeogenic genes glucose-6-phosphatase (g6pc) and phosphoenolpyruvate carboxykinase 1 (pck1) and decreased expression of the glycolytic gene pyruvate kinase (pk). Postprandial expression of the gip gene was also significantly upregulated in the foregut at 6 h. Furthermore, GIP administration modulated central appetite regulators within 1 h, increasing expression of the anorexigenic cocaine- and amphetamine-regulated transcript (cart) and decreasing expression of the orexigenic neuropeptide Y (npy) and agouti related neuropeptide (agrp). Collectively, these results indicate that in grass carp, GIP functions primarily as an appetite regulator rather than as a hypoglycemic incretin, highlighting its potential as a target for studies on appetite control in fish.

Exploring exogenous additives to enhance non-protein energy ingredient utilization in fish is highly anticipated. Epigallocatechin-3-gallate (EGCG) is a prominent polyphenol found in green tea. To assess the regulatory effect of EGCG on metabolic disorders induced by an excess of non-protein energy sources in grass carp (Ctenopharyngodon idella), five isonitrogenous diets were formulated: a control diet (23% digestible carbohydrates, 4.7% crude lipids), a high-carbohydrate (HC; 48% digestible carbohydrates, 4.7% crude lipids) diet, a high-fat (HF; 23% digestible carbohydrates, 9.6% crude lipid) diet, the HC diet supplemented with 0.05% EGCG (HC + EGCG) and the HF diet supplemented with 0.05% EGCG (HF + EGCG). The diets were fed to 450 fish (initial body weight = 8.50 g) in three replicates for eight weeks. After the feeding trial, compared with the control group, EGCG significantly alleviated the growth suppression induced by HC or HF intake (P < 0.05). Dietary EGCG supplementation downregulated the expression of fatty acid synthesis genes (srebp1, acc, and fas) (P < 0.05). Further, EGCG supplementation to the HC diet significantly increased hepatic glycogen synthesis and suppressed elevated glucose concentration through gluconeogenesis (P < 0.05). Additionally, EGCG supplementation significantly reduced excess circulating glucose by inhibiting α-amylase activities and decreasing the expression of glucose transporter 2 (glut2) in the intestines of grass carp (P < 0.05). Furthermore, in order to reveal the mechanism of EGCG affecting feeding and metabolism, transcriptome analysis on grass carp hepatocytes was conducted. The results showed that the leptin b (lepb) and G protein-coupled bile acid receptor 1 (gpbar1) were key candidate genes among differentially expressed genes from the cell transcriptome. Further in vivo studies found that the high leptin release induced by EGCG may play a pivotal role in the regulation of feed intake and appetite. Moreover, through in silico docking and microscale thermophoresis analysis, G protein-coupled bile acid receptor 1 (GPBAR1) was identified as a potential membrane receptor that directly interacts with EGCG, mediating its regulatory effect on metabolism. Therefore, plant-derived products containing high levels of EGCG could be considered as natural feed additives for regulating glucose redistribution, as they can mitigate the elevated blood glucose levels in fish caused by consuming a HC diet.

Domesticating Chinese perch to accept formulated feed is crucial for its industrial aquaculture. However, standardized feeding protocols for each domestication stage remain underdeveloped. This study investigated optimal feeding strategies and the underlying physiological pathways involved. The feeding rate experiments (5%, 8%, 11%, 14%, 17%) found that the relationship between feeding rate and domestication rate was modeled as Y=-0.5291X(2)+14.119X-23.814, with an optimal rate of 13.34% attributed to appetite stimulation via moderate starvation. Conversely, low-feeding rate induced oxidative stress, reducing the domestication rate. The feeding frequency experiments (2, 3, and 4 times/d) showed 2 times/d aligned with the natural bimodal feeding rhythm, yielding better domestication. While 4 times/d markedly enhanced feeding-related learning and memory, as indicated by upregulated fosl2 expression and increased attack frequency. However, the oxidative stress resulting from deviations from innate circadian rhythms ultimately outweighed these benefits, thereby hindering the domestication process. The feeding duration experiments (2, 4, 6, and 8 d for chilled baitfish) exhibited a significant decrease in oxidative stress after feeding for more than 6 d, which improved the acceptance of subsequent artificial feed. Moreover, the expression of learning and memory-related gene syt4 and the attack number were significantly up-regulated after feeding for 8 d, indicating enhanced feeding memory for artificially fed food. Thus, prolonging chilled baitfish feeding could enhance feeding response by increasing learning and memory, and reducing oxidative stress, thereby boosting domestication effects. Collectively, an optimized strategy (13.4% feeding rate, 2 times/d frequency, >6 d chilled baitfish feeding) achieved a higher domestication effect, providing a scientific basis for standardizing domestication and optimizing feed formulations.

This study attempted to explore the adaptability of gut microbiota in grass carp to diets with different carbohydrate-to-protein ratios in order to better understand the immunological and metabolic changes in the organism. Three different ratios of carbohydrate and protein diets (12.5%-carbohydrate 46.3%-protein (LCHP), 27.5%-carbohydrate 33.7%-protein (MCMP), and 42.5%-carbohydrate 16.9%-protein (HCLP)) were satiety-fed to grass carp. After feeding, the growth performance, gut microbial community composition and function were analyzed. Growth performance results showed that LCHP group exhibited the significantly lower specific growth ratio than MCMP group, and HCLP group displayed the significantly higher feed coefficient and lower survival rate. The community composition results showed that the abundance of the beneficial genus Cetobacterium was the highest in MCMP group, and the abundance of the harmful genera Ruminiclostridium_9 and Phreatobacter was the highest in the LCHP and HCLP groups, respectively. Furthermore, the ratio of Firmicutes to Bacteroidetes considered as an indicator of gut microbiota dysfunction, was significantly higher in the LCHP and HCLP groups than that in the MCMP group. The community functional analysis showed that the abundance levels of cofactors and vitamin metabolism were significantly lower and the abundance levels of neurodegenerative diseases were significantly higher in the LCHP and HCLP groups than those in the MCMP group. The abundance levels of energy metabolism and a range of biomolecules metabolism were significantly decreased in the HCLP group. These results suggested that high-carbohydrate diets have a greater negative impact on the gut microbiota than high-protein diets. The gut microbiota results echoed the growth performance parameters, reflecting that gut microbiota may play an important role in the influence of different carbohydrate-to-protein ratios diets on host. Bacterial genera such as Ruminiclostridium_9 and Phreatobacter may play key roles in the effects of high-protein and high-carbohydrate diets on host health and metabolism, respectively.

在新农科建设背景下,在鱼类生理学教学过程中,通过案例式和启发式教学法将思政教育渗透到教学的各环节,同时利用在线教育平台、互动式教学软件和学习型移动终端将现代信息技术融入到教学实践中,而后以修订教学大纲、健全教学评价体系等途径实现课程思政与现代信息技术的有机融合,以立德树人为教学中心环节,培养学生的综合学习能力和学科整合意识,提升学生对建设农业农村现代化、服务乡村全面振兴的使命感和责任感,为全面建设社会主义现代化培育高素质应用型人才.

基于学科与技能竞赛的水产养殖专业双创型人才培养模式强调构建以学生技能和实践为核心的教学体系,涵盖了独立实验、综合创新型实验及创业团队建设等多个方面.该体系还通过校内实践基地实训、科技小院实践,以及与各企业的合作等方式进行拓展,目的是借助学科建设和技能竞赛的推动,培育具备坚实基础和高素质的双创型复合人才,为水产行业的现代化高质量发展提供坚实的人才支撑.

Dietary carbohydrate levels can affect gut health, but the roles played by gut microbiota and gut epithelial cells, and their interactions remain unclear. In this experiment, we investigated gut health, gut microbiota, and the gene expression profiles of gut epithelial cells in grass carp consuming diets with different carbohydrate levels. Compared to the moderate-carbohydrate diet, low-carbohydrate diet significantly increased the relative abundance of pathogenic bacteria (Ralstonia and Elizabethkingia) and decreased the abundance of metabolism in cofactors and vitamins, implying a dysregulated gut microbiota and compromised metabolic function. Moreover, low-carbohydrate diet inhibited the expression levels of key genes in autophagy-related pathways in gut epithelial cells, which might directly lead to reduced clearance of defective organelles and pathogenic microorganisms. These aforementioned factors may be responsible for the imperfect organization of the intestinal tract. High-carbohydrate diet also significantly increased the abundance of pathogenic bacteria (Flavobacterium), which directly contributed to a decrease in the abundance of immune system of the microbiota. Furthermore, the active pathways of staphylococcus aureus infection and complement and coagulation cascades, as well as the inhibition of the glutathione metabolism pathway were observed. Above results implied that high-carbohydrate diet might ultimately cause severe gut damage by affecting immune function of microbiota, mentioned immune-related pathways, and the antioxidant capacity. Finally, the correlation network diagram revealed strong correlations of the differentially immune-related gene major histocompatibility complex class I antigen (MR1) with Enhydrobacter and Ruminococcus_gnavus_group in low-carbohydrate diet group, and Arenimonas in high-carbohydrate diet group, respectively, suggesting that MR1 might be a central target for immune responses in gut epithelial cells induced by gut microbiota at different levels of dietary carbohydrate. All these results provided insight in the development of antagonistic probiotics and target genes to improve the utilization of carbohydrate.

EDITORIAL article Front. Endocrinol., 06 January 2023Sec. Experimental Endocrinology Volume 13 - 2022 | https://doi.org/10.3389/fendo.2022.1125993

The discovery of melanocortins in 1916 has resulted in more than 100 years of research focused on these peptides. Extensive studies have elucidated well-established functions of melanocortins mediated by cell surface receptors, including MSHR (melanocyte-stimulating hormone receptor) and ACTHR (adrenocorticotropin receptor). Subsequently, three additional melanocortin receptors (MCRs) were identified. Among these five MCRs, MC3R and MC4R are expressed primarily in the central nervous system, and are therefore referred to as the neural MCRs. Since the central melanocortin system plays important roles in regulating energy homeostasis, targeting neural MCRs is emerging as a therapeutic approach for treating metabolic conditions such as obesity and cachexia. Early efforts modifying endogenous ligands resulted in the development of many potent and selective ligands. This review focuses on the ligands for neural MCRs, including classical ligands (MSH and agouti-related peptide), nonclassical ligands (lipocalin 2, β-defensin, small molecules, and pharmacoperones), and clinically approved ligands (ACTH, setmelanotide, bremelanotide, and several repurposed drugs).

Glucosensing evokes complex neural and endocrine responses that control glucose utilization in mammals. Until now, the glucosensing mechanism studies in fish have been mostly concentrated in carnivorous fishes and omnivorous fishes, lacking in herbivorous fishes. To lay a better understanding of herbivorous fish glucosensing mechanism, we first established a high digestible carbohydrates (HDC) intake model of grass carp with steadily reduced daily food intake compared with control diet intake. The blood glucose level of the HDC group was significantly higher than the control group within postprandial 2 h, and then no further increasing blood glucose was detected within postprandial 6 h. Within postprandial 2 h, the higher circulating glucose levels induced by HDC intake might inhibit the appetite (decreased orexigenic npy and agrp while increased anorexigenic pomc expressions) through triggering brain glucosensing mechanism (increased central slc2a2 and gck expression). After that, the combined results of unselected slc2a2 and gck expression and elevated tas1r2e-f expression after a HDC diet intake within postprandial 2–6 h suggested that the vegetarian-adapted sweet taste receptors might suppress appetite (further increased anorexigenic cartpt and pomc expressions) through affecting peripheral appetite-regulating peptides in a GCK-independent way. This result raised up the possibility that sweet taste receptors are the potential mediators involved in appetite regulation of herbivorous grass carp in response to HDC intake through peripheral glucosensing system.

Glucagon-like peptide-1 (GLP-1), a member of the proglucagon derived peptide family, is a highly effective incretin to reduce plasma glucose and inhibit food intake in mammals. The physiological function of GLP-1 has been elucidated in some 'glucose intolerant' carnivorous fishes. To lay a better understanding in fish glucose intolerance, we synthesized homologous GLP-1 peptide and explored its roles in appetite and glucose regulation under intraperitoneal (IP) injection in herbivorous grass carp which has higher glucose intolerance. The results showed that GLP-1 increased plasma glucose in grass carp. The hyperglycemic effect of the fish GLP-1 was mainly through promoting gluconeogenesis, accompanied by inhibition of glycogen synthesis and stimulation of glycogenolysis pathway. In addition, GLP-1 upregulated the expression of anorexigenic gene (cart) and decreased the orexigenic genes (npy and agrp) expression in grass carp hypothalamus as a conservative way to inhibit the appetite under GLP-1 injection after 2 h. Taken together, the hyperglycemic effect and anorectic role of GLP-1 were performed in a basically consistent manner across fishes with different food habits. What's more, the gene expressions of proglucagon yielded GLP-1 in foregut and hindgut of grass carp were significantly decreased after a meal within 24 h, indicating that fish might suppress the accumulation of plasma glucose by decreasing GLP-1 expression in a unique way to herbivorous fish. Therefore, this study provided a new perspective for illustrating the difference in glucose utilization among fishes with different food habits based on GLP-1.

在安徽六安市舒城县万佛湖水库和巢湖刘记渔场各取体质量2 500 g的鳙(Aristichthys nobilis)6尾,经100 mg/L间氨基苯甲酸乙酯甲磺酸盐麻醉后,取左右背肌200 g,采用质地多面剖析法测定肌肉质构特性;另取100 g左右背肌,采用A.O.A.C.标准方法分析常规营养成分,利用全自动氨基酸分析仪检测氨基酸组成成分,以及利用气相色谱仪检测脂肪酸组成成分,以此综合比较水库放养和池塘饲养鳙肌肉品质和营养价值的差异.质构特性结果显示,水库放养鳙肌肉的硬度和咀嚼性显著高于池塘饲养鳙.肌肉成分分析显示,水库放养鳙的肌肉粗蛋白含量显著高于池塘饲养鳙(P＜0.05);水库放养鳙肌肉中呈味氨基酸含量、必需氨基酸总量及必需氨基酸指数均显著高于池塘饲养鳙.水库放养鳙肌肉中DHA+EPA含量和∑ n-3/n-6比值也均显著高于池塘饲养鳙.综上,水库放养鳙肌肉品质和营养价值上优于池塘饲养鳙.本研究结果可为鳙养殖生产销售提供参考数据.

Regulation of gluconeogenesis rate-limiting enzymes is a novel approach to improve fish glucose utilization. Phosphoenolpyruvate carboxykinase (PEPCK), one of important gluconeogenesis rate-limiting enzymes, exists a cytosolic isoform (PEPCK-C) and a mitochondrial isoform (PEPCK-M) encoded by pck1 and pck2, respectively. Here, we first investigated the PEPCK-C/PEPCK-M activity ratio in the livers of six fishes with three different food habits. No direct relevance between food habit and the two enzymes proportion was observed among the fishes. To further explore the role of fish PEPCK isoforms regulation in response to energy change, we detected the enzyme activities and gene expressions of the isoforms in the livers of three representative fishes with different food habits after preprandial and postprandial administration. The decreased enzyme activities and increased gene expressions of two PEPCK isoforms in herbivorous grass carp were observed after postprandial administration compared with preprandial administration. Significantly decreased gene expressions and enzyme activities of these two isoforms of omnivorous crucian carp were induced by postprandial administration. In carnivorous mandarin fish, only the pck2 gene expression was down-regulated by the postprandial administration, no significant difference was seen in the enzyme activities of the two PEPCK isoforms. Therefore, the regulation of PEPCK isoforms might be one of the reasons for the discrepancy in glucose utilization among fishes with different food habits.

Plant protein is the main substitution protein for fishmeal, especially rapeseed meal, and it contains anti-nutritional factors and toxicants such as tannin. Few studies have identified clear physiological or toxicological impacts of tannin on fish. Here, our experiment evaluated the physiological and toxicological effects of tannin on grass carp (Ctenopharyngodon idellus). Different concentrations of dietary tannin (1.5, 7.2, 19.9, 39.4, 83.2 and 162.0 g kg−1 diet) were tested. Dietary tannin (≥7.2 g kg−1 diet) inhibited feed intake, and the appetite-promoting gene expression (Grehlin, NPY, Y8a and Y8b), meanwhile, increased the appetite-inhibiting gene expression (CCK and CART). Moreover, tannin addition reduced feed utilization (dietary nutrient retention, fat depot, activity of protease, lipase and amylase) of grass carp (p < .05). Besides, high dietary tannin (≥39.4 g kg−1 diet) lowered immunity (serum superoxide dismutase and catalase activities and the contents of total protein, albumin, complement component C3 and C4) (p < .05) and damaged the hepatic structure of grass carp, leading to attenuated growth in grass carp. This suggests that grass carp could not tolerate dietary tannin of >19.9 g kg−1. The second trial designed to test the alleviation the negative effect of tannin by tannase. After adding tannase with a dose of 1000 or 1500 U kg−1 to the diets, the weight gain of grass carp fed those diets was significantly increased compared with those fed the tannin and rapeseed meal addition groups (p < .05). Also, when high-level tannase was supplemented to the control diet, weight gain significantly improved. The decrease in feed intake by high dietary tannin and rapeseed meal was relieved through adding tannase in diet of grass carp, especially when tannase supplemented level reached 1000 U kg−1 diet (p < .05). This study indicates that dietary tannin (≥7.2 g kg−1 diet) negatively affects the growth of grass carp through changing feed intake, feed utilization, immunity and hepatic structure, and addition of tannase reached 1000 U kg−1 diet almost alleviate adverse effects of tannin and rapeseed meal (which included high contents of tannin) on grass carp.

Dietary supplementation with tea polyphenols (TPs) is associated with reduced diet-induced obesity and/or metabolic syndrome in mammal studies. However, TPs have rarely been related to fish metabolic syndrome caused by intensive aquaculture. In this study, TPs were supplemented to three diets with different protein to carbohydrate ratios (P38C30, P32C26, P26C42) to grass carp for 8 weeks. After the feeding trial, contrast to the anti-obesity effect in mammals, TPs improved the growth performance and spared protein of grass carp in the case of high protein and low carbohydrate diet intake. Dietary TPs supplementation reduced hepatic g6pc and pck expressions to suppress gluconeogenesis without altered glycolysis (unchanged glk and pk expression), resulted in lower plasma glucose levels compared with no supplemented diets. The hepatic glycogen was induced by dietary TPs supplementation through increasing gys expression or decreasing pyg expression. In addition, dietary TPs supplementation provided health benefits in our fish through enhancing the activities of plasma superoxide dismutase and glutathione peroxidase, and glutathione content, meanwhile, reducing the content of malondialdehyde. Therefore, TPs could be used as a natural antihyperglycemic feed additive candidate for sparing dietary protein and improving feed efficiency in aquaculture.

为了探索暂养对鳙(Aristichthys nobilis)肌肉品质和营养价值的影响,本研究检测了围网捕捞后暂养0～4周的鳙肌肉质构特性、氨基酸和脂肪酸组成以及血液中部分生化指标与抗氧化指示酶活性.质地多面剖析法检测结果显示:经过3周暂养鳙肌肉的硬度和咀嚼性显著降低,而鳙肌肉的弹性显著升高.氨基酸和脂肪酸成分分析结果显示,2周的暂养处理提高了鳙肌肉必需脂肪酸和多不饱和脂肪酸的相对含量,3周的暂养处理增加了鳙肌肉呈味氨基酸和必需氨基酸的含量.除此以外,暂养2周的鳙血浆谷丙转氨酶活性显著低于其它暂养时间;暂养2周的鳙血浆抗氧化酶超氧化物歧化酶、过氧化氢酶和谷胱甘肽过氧化物酶活性达到最大值,而脂质过氧化终产物丙二醛在该暂养时段含量最低,表明适时的暂养处理可以有效提高鳙血浆中抗氧化酶的活性.结果表明,适时的暂养处理有助于提高鳙的肌肉品质和营养价值,降低捕捞应激以利于运输.

Leptin affects food intake regulation and energy homeostasis in mammals, as opposed to mammals who have a single leptin gene, fish have duplicated leptin gene paralogues. Until now, most functional studies on fish focused on the first reported paralogue without much explanation on specific gene paralogue. This study successfully expressed two homologous recombinant mandarin fish leptin genes (LepA and LepB) for the first time. To explore the differential roles of these two gene paralogues involved in food intake and energy homeostasis, mandarin fish were treated with homologous recombinant LepA and LepB proteins by acute IP administration. The results showed that LepB inhibited the food intake of mandarin fish after acute IP administration through modifying the expressions of hypothalamic orexigenic genes, while LepA had no significant effect on its food intake. In addition, LepB administration decreased the hepatic glycogen level through regulating the gene expressions of glycogen synthase and glycogen phosphorylase in mandarin fish until 4 d, while LepA did not change the hepatic glycogen level as it failed to change the expressions of these regulatory genes. Moreover, LepA and LepB downregulated the expressions of key gluconeogenic genes (phosphofructokinase, phosphoenolpyruvate carboxykinase, and glucose-6-phosphatase), indicating both mandarin fish leptins could regulate the rate of glucose production. However, these two gene paralogues presented secondary effects on lipid metabolism as they only enhanced the triglyceride level by modifying the gene expressions of adipose triglyceride lipase or acetyl CoA carboxylase just for 1 d after IP. Therefore, LepB played an important role in food intake and glucose homeostasis regulation, while LepA showed a limited role in gluconeogenesis and lipid metabolism.

结合新兴学科免疫生态学的研究进展,围绕动物学设计性实验的开设现状,阐述了开设设计性实验的必要性,总结运用血液指标和杀菌能力测定推进动物学设计性实验教学改革的做法与体会.基于低年级本科生具有从事创新性科学研究的潜力,建议增加设计性实验的比例.