Effects of dietary choline supplementation on growth performance,lipid deposition and intestinal enzyme activities of blunt snout bream Megalobrama amblycephal fed high‐lipid diet

This study aimed to investigate the effects of dietary choline supplementation on growth, lipid deposition and intestinal enzyme activities of Megalobrama amblycephala. Fish were fed four diets with two lipid levels (50 and 150 g kg^?1) and two choline supplementations (600 and 1600 mg kg^?1) for 8 weeks. Feed conversion ratio (FCR), viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat (IPF) ratio, whole‐body and muscle lipid contents, intestinal lipase activities and lipoprotein lipase (LPL) activities all increased significantly (P < 0.05) as lipid levels increased, whereas the opposite was true for whole‐body and muscle moisture contents and intestinal amylase activities. VSI, IPF ratio and whole‐body lipid contents all decreased significantly (P < 0.05) with increasing dietary choline supplementations. Weight gain, muscle moisture content all increased significantly (P < 0.05) with increasing dietary choline supplementations when dietary lipid levels reached 150 g kg^?1, whereas the opposite was true for FCR, IPF ratio, IPF and liver LPL activities. In addition, abnormal hepatocytes were found in the liver of fish fed 150 g kg^?1 lipid with 600 mg kg^?1 choline supplementation. The result of this study indicated that extra choline supplementation can improve growth performance, intestinal enzymes activities and reduce excessive lipid deposition of M. amblycephala fed high lipid.     

Effects of dietary carbohydrate/lipid ratios on growth performance,body composition and glucose metabolism of fingerling blunt snout bream Megalobrama amblycephala

This study aimed to investigate the optimum dietary carbohydrate/lipid (CHO/L) ratio for fingerling blunt snout bream Megalobrama amblycephala (average initial weight: 6.61 ± 0.03 g). Six isonitrogenous and isoenergetic diets were formulated to contain various CHO/L ratios ranging from 1.62 to 24.20. Each diet was tested in four replicates for 10 weeks. Specific growth rate (SGR), feed conversion ratio and nitrogen and energy retention all improved significantly (P < 0.05) as dietary CHO/L ratios decreased from 24.20 to 5.64 but showed little difference (P > 0.05) as dietary CHO/L ratios ranged from 2.45 to 5.64. Hepatosomatic index increased significantly (P < 0.05) as dietary CHO/L ratios increased, whereas intraperitoneal fat ratio showed an opposite trend (P < 0.05). Opposite to moisture content, lipid content of whole body and carcass all increased significantly (P < 0.05) as dietary CHO/L ratios decreased. Liver lipid content showed little difference (P > 0.05) among all the treatments, while liver glycogen content increased significantly (P < 0.05) with increasing CHO/L ratios. High dietary carbohydrate enhanced the activities of liver hexokinase, pyruvate kinase and glucose‐6‐phosphate dehydrogenase but did not induce hyperglycaemia. Based on the second‐order polynomial regression analysis of SGR, the optimal dietary carbohydrate and lipid contents for fingerling blunt snout bream were 291.7 and 81.4 g kg⁻¹, respectively, with a corresponding dietary CHO/L ratio of 3.58.     

Dietary biotin requirement of juvenile blunt snout bream,Megalobrama amblycephala

This study was conducted to determine the optimal dietary biotin requirement of juvenile Megalobrama amblycephala. Quadruple groups of fish (initial average weight 2.01 ± 0.01 g) were fed thrice daily with six isonitrogenous and isoenergetic purified diets containing 0 (basal diet), 0.015, 0.049, 0.158, 0.624 and 2.49 mg kg^?1 biotin, respectively, for 8 weeks. Results showed that survival rate, final weight, feed intake, specific growth rate, protein efficiency ratio and nitrogen retention efficiency all increased significantly (P < 0.01) as dietary biotin levels increased from 0 to 0.049 mg kg^?1, whereas the opposite was true for feed conversion ratio. Dressout percentage, condition factor, hepatosomatic index, viscera/body ratio all showed no significant difference (P > 0.05) within the biotin range tested. Contrary to moisture content, whole‐body protein and lipid contents showed a positive correlation with dietary biotin levels. In addition, liver biotin content increased significantly (P < 0.05) with increasing dietary biotin levels up to 0.624 mg kg^?1. Hepatic pyruvate carboxylase (PC) and acetyl‐CoA carboxylase (ACC) activities both showed an increasing trend as dietary biotin levels increased. Based on the regression analysis of weight gain, hepatic PC and ACC activities, the optimal dietary biotin requirement of juvenile Megalobrama amblycephala is estimated to be 0.063, 0.071 and 0.075 mg kg^?1, respectively.     

Effects of dietary tryptophan levels on growth performance,whole body composition and gene expression levels related to glycometabolism for juvenile blunt snout bream,Megalobrama amblycephala

To investigate the effects of dietary tryptophan on growth and glycometabolism in juvenile blunt snout bream, 450 fish (initial weight 23.33 ± 0.03 g) were fed six practical diets with graded levels of tryptophan (from 0.79 g/kg to 5.96 g/kg dry matter) for 8 weeks. Results showed that final weight, per cent weight gain (PWG), protein efficiency rate, feed intake and feed conversion ratio (FCR) were significantly improved by 2.80 g/kg diet. The maximum values of protein and ash were observed in 2.80 g/kg diet, while moisture was minimum. Lipid content of fish fed 3.95 g/kg diet was significantly higher than other diets. The highest plasma insulin‐like growth factor‐1 (IGF‐1) content was observed in 0.79 g/kg diet. In the liver, IGF‐1 mRNA levels were significantly downregulated by 2.80 g/kg dietary tryptophan, while glucokinase levels were by 3.95 g/kg, while glucose‐6‐phosphatase and phosphoenolpyruvate carboxykinase mRNA levels showed a converse trend compared with IGF‐1. Based on PWG and FCR, the optimal dietary tryptophan level was determined to be 1.99 g/kg (6.20 g/kg of dietary protein) and 1.96 g/kg (6.11 g/kg of dietary protein), respectively, using broken‐line regression analysis.     

Dietary methionine requirement of juvenile blunt snout bream (Megalobrama amblycephala) at a constant dietary cystine level

A 9‐week feeding trial was conducted to investigate the dietary methionine requirement of juvenile Megalobrama amblycephala at a constant dietary cystine level. Six semipurified diets were formulated to contain graded dietary methionine levels from 3.9 to 15.4 g kg^?1 in about 2.5 g kg^?1 increments in the presence of 2.2 g kg^?1 cystine. Results showed that specific growth rate (SGR) and protein efficiency ratio (PER) significantly increased with increasing dietary methionine levels from 3.9 to 12.4 g kg^?1 and thereafter kept stable. Maximum protein productive value (PPV), nitrogen retention efficiency (NRE) and liver weight were observed in 8.5 g methionine kg^?1 diet. Protein contents in whole fish body were positively correlated with dietary methionine level, while lipid contents were negatively correlated with it. Morphological index and hepatic glutamate‐pyruvate transaminase (GPT) activities were independent of dietary methionine levels. However, dietary methionine supplementation significantly improved haematological parameters, plasma methionine and total essential amino acid contents and hepatic glutamate‐oxaloacetate transaminase (GOT) activities. Analysis of dose response using broken‐line regression on the basis of SGR and PPV versus dietary methionine level estimated the optimum dietary methionine requirements of juvenile M. amblycephala to be between 8.5 and 8.4 g kg^?1 of diet (25.0 and 24.7 g kg^?1 of protein) in the presence of 2.2 g kg^?1 cystine, respectively. Hence, the corresponding total sulphur amino acids requirements of this species were calculated to be 10.7 and 10.6 g kg^?1 of diet (31.5 and 31.2 g kg^?1 of dietary protein).     

Dietary niacin requirement of juvenile blunt snout bream Megalobrama amblycephala based on a dose–response study

This study aimed to determine the optimal dietary niacin requirement of juvenile Megalobrama amblycephala. Fish, with an average weight of 3.62 ± 0.02 g, were randomly divided into six groups and fed six purified diets with graded levels of niacin (0, 10, 20, 30, 40 and 50 mg/kg) three times daily for 8 weeks. The survival rate, weight gain (WG), feed conversion ratio, protein efficiency and protein retention all significantly improved (p < .05) as the dietary niacin level increased from 0 to 30 mg/kg but showed no significant difference (p > .05) with further increases in niacin levels. The supplementation of 30 mg/kg niacin also led to a significant (p < .01) reduction in the viscerosomatic index, hepatosomatic index and mesenteric fat index. The dietary niacin levels exhibited minimal effects on whole‐body moisture and ash content (p > .05) but exerted a significant (p < .05) influence on protein and lipid contents and liver nicotinamide concentrations with high values obtained in fish receiving greater than 30 mg/kg of niacin. In addition, moderate levels of niacin lowered plasma triglycerides, non‐esterified fatty acid and low‐density lipoprotein cholesterol concentrations (p < .05). Based on the broken‐line regression analysis of WG and liver nicotinamide content, the optimal dietary niacin requirement of juvenile blunt snout bream was 31.25 and 30.62 mg/kg, respectively.     

Combined effects of dietary fructooligosaccharide and Bacillus licheniformis on growth performance,body composition,intestinal enzymes activities and gut histology of triangular bream (Megalobrama terminalis)

This study was conducted to investigate the effects of fructooligosaccharide (FOS) and Bacillus licheniformis (B. licheniformis) on growth performance, body composition, intestinal enzymes activities and gut histology of Megalobrama terminalis. Nine experimental diets were formulated to contain three FOS levels (0, 3 and 6 g kg^?1) and three B. licheniformis levels (0, 1 and 5 × 10⁷ CFU g^?1) following a 3 × 3 factorial design. Accordingly, diets were named as 0/0, 0/3, 0/6, 1/0, 1/3, 1/6, 5/0, 5/3 and 5/6 (B. licheniformis/FOS). At the end of the 8‐week feeding trial, weight gain (WG) and specific growth rate (SGR) of fish fed 6 g kg^?1 FOS were both significantly (P < 0.01 and P < 0.05) higher than that of the other groups in terms of dietary FOS levels. Besides, WG and SGR of fish fed 1 × 10⁷ CFU g^?1 B. licheniformis were significantly (P < 0.05) higher than that of the control group in terms of dietary B. licheniformis levels. In addition, a significant interaction (P < 0.05) between dietary FOS and B. licheniformis was observed in finial weight, WG, SGR as well as the survival rate with the highest values all observed in fish fed diet 1/3. Hepatosomatic index, carcass lipid content, lipase activities as well as microvilli length increased significantly (P < 0.05) from 0 to 1 × 10⁷ CFU g^?1, but no significant difference (P > 0.05) was observed in terms of dietary FOS levels. In addition, a significant (P < 0.05) interaction of FOS and B. licheniformis was observed in both protease and Na⁺, K⁺‐ATPase activities with the highest value obtained in fish fed diet 1/3. The results indicated that the dietary applications of dietary FOS and B. licheniformis alone or in combination can significantly improve the growth performance, survival rate, intestinal enzymes activities as well as microvilli length of triangular bream. In addition, there is a significant interaction between dietary FOS and B. licheniformis. The best combination for this species is 3 g kg^?1 FOS with 1 × 10⁷ CFU g^?1 B. licheniformis.     

饲料不同淀粉水平对团头鲂成鱼生长性能、消化酶活性及肌肉成分的影响

为探讨饲料淀粉水平对团头鲂成鱼生长、消化酶活性和肌肉成分的影响,选用初始均重为(161±2.7)g的团头鲂成鱼360尾,随机分成6组(每组3个重复),分别投喂含淀粉17.1%、21.8%、26.4%、32.0%、36.3%和41.9%的等氮等脂饲料9周。结果发现,团头鲂成鱼成活率和特定生长率不受饲料淀粉水平影响,但饲料添加适量淀粉能提高饲料和蛋白利用率,淀粉水平对肝脏和肠道中的总蛋白酶和纤维素酶活性不产生影响,却显著影响淀粉酶活性。肝体比、肝糖原和肌肉粗脂肪含量随饲料淀粉含量的增加而显著增加,血清血糖、胆固醇和甘油三酯含量不受饲料淀粉水平的显著影响,饲料中添加过量淀粉显著降低了血清补体3和补体4含量。以蛋白质效率和饲料效率为评价指标,经折线模型回归分析,得到团头鲂成鱼饲料中淀粉的适宜添加量分别为饲料干重的34.1%和31.4%,但考虑到血清补体的活性,团头鲂成鱼日粮淀粉水平不应超过36.3%。     

Dietary isoleucine requirement of juvenile blunt snout bream,Megalobrama amblycephala

A 9‐week feeding trial was conducted to estimate the dietary isoleucine requirement of juvenile blunt snout bream. Six isonitrogenous and isoenergetic experimental diets were formulated to contain graded isoleucine levels ranging from 5.3 to 20.1 g kg^?1 dry diet. At the end of the experiment, weight gain (WG), specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER) increased with increasing dietary isoleucine level up to 11.1 g kg^?1 dry diet, and dietary isoleucine level above 14.2 g kg^?1 dry diet declined these performances. Dietary isoleucine levels (14.2 and 17.3 g kg^?1 dry diet) significantly improved whole‐body protein content, but decreased whole‐body lipid, plasma triglyceride and cholesterol contents. Significantly lower visceral fat index (VFI) in fish fed with 14.2 g kg^?1 dietary isoleucine was observed compared to those fed with deficient or excessive isoleucine. Dietary isoleucine supplementation significantly increased plasma isoleucine concentration, while plasma valine and leucine concentrations showed a reversed trend. Dietary isoleucine levels regulated the target of rapamycin (TOR) gene expression and improved plasma superoxide dismutase (SOD) activity in juvenile blunt snout bream. Based on second‐order polynomial regression model analysis of SGR and FER, the optimum dietary isoleucine requirement was estimated to be 13.8 g kg^?1 dry diet (40.6 g kg^?1 dietary protein) and 14.0 g kg^?1 dry diet (41.2 g kg^?1 dietary protein), respectively.     

Dietary histidine requirement of juvenile blunt snout bream (Megalobrama amblycephala)

An eight‐week feeding trial was conducted to determine the dietary histidine requirement of juvenile blunt snout bream. The results showed that final body weight, weight gain rate and specific growth rate significantly increased with increasing dietary histidine levels up to 9.9 g/kg (p < .05) and decreased gradually thereafter, while feed conversion ratio showed a converse trend. The survival rate, condition factor, viscerosomatic and hepatosomatic index were not significantly affected by the graded dietary histidine levels (p > .05). About 9.9 g/kg dietary histidine level significantly improved whole‐body protein and lowered moisture content. The contents of plasma total protein, cholesterol, urea and triglyceride levels were not significantly affected by dietary histidine levels. About 9.9 g/kg dietary histidine level significantly upregulated target of rapamycin and insulin‐like growth factor mRNA levels (p < .05), and 12.1 g/kg and 14.2 g/kg dietary histidine levels significantly upregulated eukaryotic translation initiation factor 4E‐binding protein 2 and ribosomal protein S6 kinase‐polypeptide 1 mRNA levels (p < .05). Based on second‐degree polynomial regression analysis of weight gain rate, and specific growth rate against dietary histidine levels, the dietary histidine requirement for juvenile blunt snout bream was estimated to be 11.2 g/kg of diet, corresponding to 36.1 g/kg of dietary protein.     

饲料锌对团头鲂幼鱼生长性能、血清生化指标和抗氧化功能的影响

以酪蛋白和明胶为蛋白源,七水硫酸锌(Zn SO4·7H2O)为Zn源,分别配制成7种Zn含量(7.4 mg/kg、20.3 mg/kg、32.1 mg/kg、51.0 mg/kg、84.4 mg/kg、169.7 mg/kg、332.4 mg/kg)的半纯化饲料,投喂初始体重为(3.6±0.1)g团头鲂(Megalobrama amblycephala)12周,考察Zn对团头鲂幼鱼生长性能、血清生化指标和抗氧化功能的影响,确定团头鲂幼鱼对饲料Zn的需要量。结果表明,随着饲料Zn含量增加,团头鲂增重率、特定生长率和全鱼Zn含量呈先增加后稳定的趋势;全鱼水分含量显著降低(P0.05),粗蛋白含量显著增加。饲料Zn含量对团头鲂饲料系数无显著影响。饲料中添加Zn显著影响血清总蛋白、尿素氮、高密度脂蛋白胆固醇、总胆固醇以及甘油三酯含量,而对血清白蛋白含量和碱性磷酸酶活性无显著影响。随着饲料中Zn含量的增加,团头鲂肝丙二醛含量显著降低(P0.05),而肝过氧化氢酶和超氧化物歧化酶活性在各处理间均无显著差异。折线回归分析表明,团头鲂幼鱼(体重3.6~26.7 g)获得最佳生长时对饲料Zn需要量为32.6 mg/kg,获得最大鱼体Zn含量时Zn的需要量为47.6 mg/kg。本研究旨在确定团头鲂幼鱼对饲料中Zn的需要量,为配制团头鲂高效环保饲料提供科学依据。     

Dietary choline requirement for juvenile blunt snout bream,Megalobrama amblycephala

A 12‐week feeding trial was conducted to determine dietary choline requirement for juvenile Megalobrama amblycephala. The basal diet was formulated to contain 310 g kg^?1 diet from vitamin‐free casein and gelatine. Choline chloride was supplemented to the basal diet to formulate six purified diets containing 0, 250, 500, 1000, 2000 and 4000 mg kg^?1, respectively. Each diet was randomly fed to quadrupled groups of Megalobrama amblycephala with initial average weight 1.84 ± 0.04 g in a flow‐through system. Results showed weight gain was increased significantly with increasing dietary choline levels (P < 0.01). Lipid content of liver decreased significantly as dietary choline concentration increased (P < 0.01), whereas lipid content of dressed carcass showed opposite trend (P < 0.01), and lipid content of whole‐body was unaffected by dietary choline supplementation. Broken‐ line regression of weight gain, liver and muscle choline concentration showed choline requirements of Megalobrama amblycephala of 1198, 1525 and 1365 mg kg^?1, respectively. In addition, dietary choline supplementation significantly improved lipid content of dressed carcass but not the content of whole body of blunt snout bream.     

Effects of complete fish meal replacement by rice protein concentrate with or without lysine supplement on growth performance,muscle development and flesh quality of blunt snout bream (Megalobrama amblycephala)

An 8‐week feeding trial was conducted to evaluate the effects of fish meal (FM) replacement by rice protein concentrate (RPC) with supplementation of microcapsule lysine (ML) or crystalline lysine (CL) on growth performance, muscle development and flesh quality of blunt snout bream. Four isonitrogenous and isoenergetic diets were formulated, including FM diet (containing 50 g/kg FM), RPC diet (FM replaced by RPC), MRPC diet (FM replaced by RPC with ML supplementation) and CRPC diet (FM replaced by RPC with CL supplementation). Fish fed FM diet had significantly higher weight gain, feed efficiency, protein efficiency ratio and nitrogen and energy utilization than that of RPC group, but showed no statistical difference with other treatments. In addition, fish fed RPC diet showed higher muscle fibre frequency in the 20‐ to 50‐μm class but lower >50‐μm class and higher cooking loss than that of the other groups. Furthermore, no significant difference was found in whole‐body proximate compositions, frequency distribution of <20‐μm‐diameter fibres, texture, muscle content, collagen, pH 24 hr post‐mortem and sensory quality. The results showed that RPC supplemented with ML or CL could replace fishmeal without any adverse effects on growth performance and flesh quality for blunt snout bream.     

Dietary histidine affects intestinal antioxidant enzyme activities,antioxidant gene expressions and inflammatory factors in juvenile blunt snout bream (Megalobrama amblycephala)

Six semipurified diets of graded histidine levels (from 4.1 to 14.2 g/kg) were fed to fish for 8 weeks. The results showed that the intestinal content of malondialdehyde (MDA), activities of total superoxide dismutase (T‐SOD) and glutathione peroxidase (GPx) were noticeably lower in 8.0 g/kg diet compared to control group. While the lowest activities of copper–zinc superoxide dismutase (Cu/Zn‐SOD) and manganese superoxide dismutase (Mn‐SOD) were observed in 9.9 g/kg diet, the intestinal activities of total antioxidant capacity (T‐AOC) and catalase (CAT) in 14.2 g/kg diet were noticeably higher than those in 8.0 and 9.9 g/kg diets. Plasma biochemical indexes were not significantly affected by dietary histidine levels. In the intestine, the Kelch‐like ECH‐associated protein 1 (Keap1) mRNA levels were increased in 8.0 g/kg diet, which suppressed the nuclear translocation of nuclear factor E2‐related factor 2 (Nrf2), and subsequently decreased CAT, GPx1, Cu/Zn‐SOD and Mn‐SOD expression levels. The lowest mRNA levels of interleukin 8 (IL‐8) and tumour necrosis factor‐α (TNF‐α) were observed in 8.0 g/kg diet, whereas the highest mRNA levels of transforming growth factor‐β (TGF‐β) and interleukin 10 (IL‐10) were observed in 8.0 g/kg diet. These results indicated that dietary histidine plays a major role in maintaining intestinal health in juvenile blunt snout bream.     

Effects of the total fish meal replacement by soybean meal on growth parameters,serum biochemistry,and hepatic and intestinal histology of juvenile blunt snout bream (Megalobrama amblycephala)

ABSTRACT

Fish meal is the main protein source in fish diet, but due to its unsustainability, it has to be replaced with more sustainable protein sources, such as soybean meal (SBM), in fish feeds. As SBM often produces negative effects on fish growth and health, we conducted an eight-week trial of complete fish meal replacement with SBM in the diet of juvenile (48.2 ± 0.55 g) blunt snout bream (Megalobrama amblycephala), a herbivorous cyprinid fish native to the Yangtze basin (China). SBM-fed fish exhibited: a worsened growth performance; improved survival rate (P > 0.05); elevated serum triglycerides and total cholesterol but reduced low-density lipoprotein in plasma (P < 0.05); mild lipid droplet accumulation and swelling of the liver; elevated goblet cell counts and mild signs of enteritis in the intestines. With negligible effects on growth and mild effects on health, M. amblycephala appears to be comparatively tolerant of SBM, but total fish meal replacement is not recommended. Future studies should aim to identify the SBM tolerance threshold in long-term growth trials.     

Complete replacement of fish meal by plant protein ingredients with dietary essential amino acids supplementation for juvenile blunt snout bream (Megalobrama amblycephala)

Six extruded diets were formulated with a graded level of fish meal (FM); diet 1 and diet 2 were formulated with 80 g/kg FM; diet 3 and diet 4 were formulated with 40 g/kg FM; and diet 5 and diet 6 were devoid of FM. Hence, diet 2, diet 4 and diet 6 were supplemented with essential amino acids (EAAs). The diets were fed throughout an eight‐week feeding trial. The results revealed that specific growth rate (SGR), feed conversion ratio (FCR), body weight gain (BWG) and protein efficiency ratio (PER) were influenced by FM reduction and improved by the addition of EAA (p < 0.05). A survival rate (SR), whole body content of protein, lipid, moisture and ash, and plasma total protein (TP), albumin (ALB), triglyceride (TG) and urea (UN) did not influence by dietary treatments (p > 0.05). Additionally, target of rapamycin (TOR) pathway did not influence by dietary treatments (p > 0.05). Expression levels of hepatic peptide transporter 1 (Pept1) and peptide transporter 2 (Pept2) decreased against FM reduction and improved significantly in the groups fed diet 4 and diet 6. In summary, the findings revealed that diet containing plant proteins mixture supplemented with EAA could totally replace FM in the practical diet of blunt snout bream.     

Growth performance and TOR pathway gene expression of juvenile blunt snout bream,Megalobrama amblycephala,fed with diets replacing fish meal with cottonseed meal

A 16‐week feeding trial was conducted to assess the effects of replacing fish meal (FM) with cottonseed meal (CM) on the growth performance, feed utilization, plasma biochemical composition and target of rapamycin (TOR) pathway gene expression of juvenile blunt snout bream (Megalobrama amblycephala). Five isonitrogenous (36% crude protein) and isoenergetic (16 MJ kg^?1) diets with graded replacing levels of CM (replacing 0, 25, 50, 75 and 100% FM with CM) and similar lysine and methionine concentrations were fed to triplicate groups of fish. Results revealed that specific growth rate (SGR), feed intake and protein efficiency ratio (PER) of group fed with diets replacing FM with CM up to 50% were significantly higher than others (P < 0.05). However, final body weight and feed conversion ratio (FCR) remained similar up to 25% and thereafter significantly decreased and increased, respectively, as the replacement level increased (P < 0.05). Replacement levels significantly decreased hepatosomatic index and viscerosomatic index (P < 0.05), but did not significantly affect condition factor and whole body compositions. Free gossypol mainly accumulated in liver and significantly increased in diets CM75 and CM100 than CM0 (P < 0.05). Replacement significantly influenced plasma urea contents (P < 0.05). Meanwhile, increasing replacement of FM with CM in diets increased insulin‐like growth factor I (IGF‐1) gene expression in liver of blunt snout bream. Target of rapamycin (TOR) gene expression in diet CM100 was significantly lower than that in diets CM0 and CM75, while the eukaryotic translation initiation factor 4E‐binding protein 2 (4E‐BP2) gene expression was not affected by the replacement level of CM in diets. Therefore, based on final body weight and FCR, it suggested that up to 25% of FM (150 g kg^?1 in basal diet) could be replaced by CM in diets, which was 112.5 g kg^?1 FM and 192.9 g kg^?1 CM, for juvenile blunt snout bream.     

果寡糖对急性氨氮应激下团头鲂非特异性免疫指标的影响

为研究氨氮应激条件下果寡糖对团头鲂(Megalobrama amblycephala)非特异免疫指标的影响,试验选择360尾初重为13.5 g的团头鲂随机分为3组,每组4个重复,每缸30尾鱼,对照组投喂基础日粮,试验组分别投喂果寡糖(FOS)添加量为0.4%和0.8%的日粮,饲养8周,养殖试验结束后,用10 mg/L的NH4Cl对24尾鱼进行氨氮应激试验。试验结果显示,氨氮应激前,0.4%FOS组的血液谷丙转氨酶(GPT)活性显著低于对照组和0.8%FOS组,在氨氮应激后,0.4%FOS组的GOT活性有降低的趋势,但仅在24 h时显著低于0.8%组,0.8%组和对照组之间并无显著差异;血清酸性磷酸酶、补体3(C3)、补体4(C4)、酚氧化酶都出现先升高后降低的趋势,分别在应激后的3、24、12、12 h达到最大值。此外,应激前0.4%FOS组补体C3、C4、酚氧化酶的活性都显著高于对照组,应激后0.4%FOS组C3在3 h处显著高于对照组,但是在其它时间点各组差异并不显著,果寡糖添加水平和采样时间对这些免疫指标都无显著的交互作用。结果表明饲料中添加0.4%的果寡糖能够提高团头鲂的免疫力指标活性,提高了团头鲂抗氨氮应激的能力。     

Graded replacing fishmeal with canola meal in diets affects growth and target of rapamycin pathway gene expression of juvenile blunt snout bream,Megalobrama amblycephala

A feeding trial was conducted to assess the effects of replacing fishmeal (FM) with canola meal (CM) on the growth performance, feed utilization and related gene expression of juvenile blunt snout bream (Megalobrama amblycephala). Fishes were fed with five isonitrogenous (330 g/kg crude protein) and isoenergetic (15 MJ/kg) diets for 16 weeks, which was graded replacing levels of fishmeal (replacing 0, 37.5, 75, 112.5 and 150 g/kg FM with CM). The results revealed that specific growth rate, feed efficiency ratio and protein efficiency ratio of the groups with replacement level up to half were significantly higher than the others, while feed intake was inverse. Peptide transporter 1 (PepT1) mRNA level in the gut was significantly up‐regulated in groups CM25 and CM50 compared to other groups. Relative gene expression of IGF‐1 among groups was extremely significant based on the nonparametric test. Replacement of FM with CM caused a reduction in the hepatic expression of target of rapamycin (TOR), while significant increase trends were observed in hepatic genes of protein kinase B (AKT) and eIF4‐binding protein (4E‐BP2). However, TOR gene expression in the gut was significantly up‐regulated first and then down‐regulated, while mRNA levels of 4E‐BP2 and S6K1 in the gut were first significantly decreased and then increased in CM75, finally significantly decreased to the lowest. The overall results indicated that up to 75 g/kg FM could be replaced by CM (350.5 g/kg CM) in the diets for juvenile blunt snout bream. Besides, these signalling molecules could explain further the mechanisms that juvenile blunt snout can only maintain optimal growth performance up to 75 g/kg FM replacement with CM.     

Effects of dietary linolenic acid on growth,fatty acid composition,immune function and antioxidant status of juvenile blunt snout bream,Megalobrama amblycephala

A nine‐week feeding trial was performed to determine the dietary linolenic acid (LNA; 18:3n–3) requirements of juvenile blunt snout bream. Six iso‐nitrogenous, semi‐purified diets were prepared with different concentrations of LNA (0–25 g/kg). Dietary LNA had no significant effects on survival rate. However, final fish weight, weight gain (WG), specific growth rate (SGR) and feed efficiency ratio (FER) increased with increasing dietary LNA concentrations up to 20 g/kg. Dietary LNA increased muscle LNA and total n‐3 polyunsaturated fatty acid (PUFA) contents, but decreased total saturated fatty acid content. Fish fed 20 g/kg LNA had the highest plasma alkaline phosphatase activity, total protein, albumin and white blood cell count levels. Additionally, fish fed 20 g/kg LNA had higher triglyceride levels than control fish. Plasma glucose increased with increasing dietary LNA concentrations. Superoxide dismutase and glutathione peroxidase activities significantly increased with increasing dietary LNA concentrations up to 15 g/kg. Based on SGR and FER, the optimal dietary LNA requirements of juvenile blunt snout bream were 17.5 and 15.6 g/kg respectively.