The level of 1C diets fed prior to cell isolation affects lipid metabolism in primary liver cells isolated from Atlantic salmon (Salmo salar)

Liver cells were isolated from 6 fish fed a diet containing 12.1 g methionine/kg, 11.02 mg vitamin B6/kg, 0.20 mg vitamin B12/kg and 7.80 mg folate/kg (named high‐1C diet). These cells were compared to liver cells isolated from 6 fish fed a diet containing 6.7 g methionine/kg, 7.01 g vitamin B6/kg, 0.15 mg vitamin B12/kg and 2.60 mg folate/kg (named low‐1C diet). Isolated cells were plated on 6‐well plates in Leibovitz medium and treated with 10 mM metformin, 10 mM metformin for 24 hr followed by 0.4 mM oleic acid (OA) for 24 hr or only 0.4 mM OA for 24 hr. The cells were compared to untreated controls added only the medium. All cells were harvested 48 hr after being plated. Cells isolated from Atlantic salmon fed low‐1C diets showed higher gene expression of MGAT‐2 (p < .0001), CPT‐1 (p = .028), FAS (p = .0006), LXR (p = .020), ACC (p = .032) and MnSOD (p < .0001). The low‐ or high‐1C diets fed prior to cell isolation had no effect on gene expression of ApoB100, PPARa, CD36, SREBP‐2 or Bcl‐2. Metformin treatment increased the expression of the anti‐apoptotic protein Bcl‐2 (p = .0001) indicating an anti‐apoptotic effect. Metformin generally increased the expression of genes associated with lipid oxidation and transport, but decreased the expression of genes associated with cholesterol metabolism confirming our earlier results using this model.     

Efficacy of crystalline methionine and microencapsulation methionine in diets for Pacific white shrimp Litopenaeus vannamei

An 8‐week growth trial was conducted to evaluate the efficacy of crystalline methionine (C‐Met) or microencapsulated methionine (M‐Met) in practical diets for Pacific white shrimp Litopenaeus vannamei. A high fishmeal reference diet was formulated with 15% fishmeal, and then, soybean meal (SBM) was used to replace 50% fishmeal as a low fishmeal basal diet (7.5% fishmeal). Graded levels (0.1%, 0.15% and 0.2%) of methionine originating from C‐Met or M‐Met were added to the basal diet. Each diet was randomly assigned to three tanks (40 shrimps per tank) in an indoor flow through seawater system. The results showed that the shrimp fed the basal diet with 0.15% or 0.20% methionine originating from 0.375% or 0.5% M‐Met had significantly higher final weight and weight gain as compared to shrimp fed the basal diet. The supplementation M‐Met in the basal diets resulted in increased serum ammonia in shrimp. Hepatopancreas amylase activity of shrimp showed a decreasing trend with increasing methionine supplementation, which is in contrast with the upswing trend in trypsin at pancreatic segment. This study indicated that the diets supplemented with 0.15% or 0.20% of methionine from M‐Met (0.58% or 0.65% of dietary methionine respectively) were effective in improving the nutritional value of SBM‐based diets deficient in methionine (0.48%) for the Pacific white shrimp.     

Nutritional quality of some improved cultivars of cowpea

The seeds of 13 improved cowpea cultivars were analysed for proximate composition, methionine, tryptophan and polyphenols. Considerable genetic variations were observed for the contents of protein, nonprotein nitrogen, limiting amino acids and polyphenols. The globulins contributed about 50% of the total seed proteins. A significant proportion of proteins of high protein cultivars was found to be insoluble. The proteins of most of the cultivars were found deficient in methionine and tryptophan. Methionine and tryptophan levels were negatively correlated with protein and positively correlated with carbohydrate contents. The cultivars with colored seed coats contained higher amounts of polyphenols. The difference in polyphenol content between various cultivars were due to seed coat polyphenols.     

Effect of diets containing low levels of methionine and oxidized oil on body composition, retina structure and pigmentation success of Japanese flounder

Diets reduced in methionine (Met) and with oxidized oil were formulated to induce visual deficiencies in Japanese flounder, Paralichthys alivaceus (T. & S.), in an attempt to link vision with pigmentation development. Even though Met-deficient diets have proved to be cataractogenic in salmonids, no cataracts were formed in flounder eye. However, both diets produced an abnormal morphology in the retinal pigment epithelium and the photoreceptor outer segments of the fish retina. The high presence of dead nuclei in the photoreceptor inner segment suggests a loss in the visual capability of fish fed these two diets, which produced lower pigmentation success than the control. A significant correlation was also found between pigmentation success and fatty acid composition (docosahexaenoic acid and arachidonic acid) of the head polar lipid fraction. The results suggest that a deficient intake of amino acids and fatty acids produces a change in retinal structure and composition, leading to reduced visual capability and suppression of the development of normal pigmentary pattern in flatfish.     

豆粕型饲料中添加蛋氨酸对江黄颡鱼生长的影响

研究了在豆粕型饲料中添加不同浓度的蛋氨酸对江黄颡鱼生长的影响。试验鱼分为3个组,蛋氨酸的添加量分别为0、0.2%、0.4%,分别对应Ⅰ、Ⅱ、Ⅲ组,Ⅰ组设为对照组,饲养周期为8周。试验结果表明,Ⅱ组、Ⅲ组的质量增长率显著高于对照组(P<0.05),其中Ⅱ组质量增长率最高(176.22±3.56)%;Ⅱ组的成活率显著高于对照组(P<0.05);各组的饲料系数与对照组比较无显著性差异(P>0.05),Ⅲ组饲料系数最小(2.60±0.13);各试验组之间的摄食量差异不显著(P>0.05),Ⅱ组的摄食量较对照组高12.50%。在本研究条件下,建议蛋氨酸的添加量为0.2%~0.4%。     

Juvenile Atlantic salmon decrease white trunk muscle IGF‐1 expression and reduce muscle and plasma free sulphur amino acids when methionine availability is low while liver sulphur metabolites mostly is unaffected by treatment

We previously reported that juvenile Atlantic salmon with mean initial BW 11.5 g offed a methionine deficient diet had lower weight gain due to a reduced protein accretion, while lipid gain was unaffected. Muscle of the fish fed the methionine deficient diet was depleted for sulphur amino acids, while in liver, the concentration of these metabolites was maintained within narrow limits. We speculated whether this could be due to an increased muscle proteolysis to support a prioritized liver metabolism in fish fed the low methionine diets. In this study, we assessed whether genes associated with muscle proteolysis increased under methionine deficiency. The composition of the diets was similar to those used previously containing 1.6 or 2.1 g Met/16 g N. We confirmed that the fish fed the low methionine diet gained less protein compared to fish fed the DL‐methionine enriched diet (P = 0.014), but growth did not reduce significantly. Also the deficient fish maintained the concentrations of liver sulphur amino acids and reduced muscle free methionine. Several of the other free amino acids within muscle increased. Further, methylation capacity was maintained in liver but reduced in the muscle (P = 0.78 and 0.04, respectively). Gene expression of muscle IGF‐1 was lower (P = 0.008) and myosin light chain 2 tended (MLC2, P = 0.06) to be reduced in fish fed low methionine diet, concurrently the activity of cathepsins B+L increased (P = 0.047) in muscle of fish fed the low methionine diet. Gene expression of the muscle‐specific E3 ubiquitine ligases (Murf and MaFbx) was not affected by treatment. Thus, the lower protein gain observed in fish fed the low methionine diet may be caused by reduced protein synthesis in line with the reduced IGF‐1 gene expression in the white trunk muscle. Thus, to support metabolism, the dietary protein needs to be balanced in amino acids to support metabolism in all compartments of the body and secure maximal protein gain.     

The effect of dietary methionine concentrations on growth performance of juvenile Nile tilapia (Oreochromis niloticus) fed diets with two different digestible energy levels

A growth trial was conducted to examine the effect of dietary digestible energy (DE) content on methionine (Met) utilization and requirement in juvenile Nile tilapia (Oreochromis niloticus). Ten iso‐nitrogenous (288 g kg^?1 protein) practical diets, with two DE levels (10.9 MJ kg^?1; 12.4 MJ kg^?1) and five methionine supplementation levels (0, 1, 2, 4 and 6 g kg^?1), were hand‐fed twice daily to triplicate groups of Nile tilapia (initial body weight 8.95 ± 0.06 g) for 8 weeks. Weight gain (WG) and specific growth rate (SGR) increased significantly with increasing dietary methionine concentration at the same DE content (P < 0.001). At the same dietary methionine level, WG and SGR of fish fed high‐DE diets were significantly higher than that of fish fed low‐DE diets (P = 0.0001), although no interaction was found between dietary DE and methionine supplementation. Based on quadratic regression analysis between dietary methionine concentration and weight gain, optimal methionine requirement for maximum growth, expressed as g Met required kg^?1 diet (low‐ versus high‐DE diets), increased as diet DE concentration increased (7.34 versus 9.90 g kg^?1 diet, respectively; with cysteine 4.70 g kg^?1 diet). The results indicated that diet DE content affects methionine utilization and requirement in juvenile Nile tilapia, fish fed high‐DE diets required more methionine for maximum growth.     

Assessing the bioavailability of L‐methionine and a methionine hydroxy analogue (MHA‐Ca) compared to DL‐methionine in rainbow trout (Oncorhynchus mykiss)

Different synthetic forms of supplemental methionine (Met) are produced commercially by various manufacturers. Limited information exists on the bioavailability of these different forms in commercially relevant fish species. The objective of this study was to compare the relative bioavailability of L‐methionine and a methionine hydroxy analogue calcium salt (MHA‐Ca) to DL‐methionine in a commercially relevant species, rainbow trout, using a linear slope‐ratio assay. In addition, the ability of the rainbow trout to effectively convert the D‐isomer of methionine into the biologically active L‐isomer was studied by comparing the relative bioavailability of L‐methionine to DL‐methionine. Nine (9) diets were created from a methionine‐deficient basal diet which was supplemented with graded equimolar levels of methionine (0.1%, 0.2%, 0.3% of diet by weight) from either DL‐methionine, L‐methionine and methionine hydroxy analogue calcium salt (MHA‐Ca). Diets were fed in triplicate (IBW = 24.0 ± 0.6 g) for 12 weeks using a pair‐feeding protocol. The basal diet was formulated to be deficient in both methionine (0.5%) and cysteine (0.3%), whereas meeting all other known nutritional requirements of rainbow trout. MHA‐Ca was found to be less available (P < 0.05) than DL‐methionine with relative bioavailability values of 69%, 60% and 73% based upon weight gain, growth rate (TGC) and retained nitrogen values respectively. No significant differences (P > 0.05) in bioavailability were found between DL‐methionine and L‐methionine. These findings lead to the conclusion that differences in bioavailability do exist between sources of synthetic methionine, additionally findings suggest that rainbow trout are able to effectively convert the D‐isomer of methionine into the L‐isomer without significantly affecting fish performance.     

Effect of methionine on intestinal enzymes activities, microflora and humoral immune of juvenile Jian carp (cyprinus carpio var. Jian)

An 8-week feeding experiment was conducted to determine the effect of dietary methionine supplementation on intestinal microflora and humoral immune of juvenile Jian carp (initial weight of 9.9 ± 0.0 g) reared in indoor flow-through and aerated aquaria. Eight amino acid test diets (350 g kg⁻¹ crude protein, CP), using fish meal, soybean-condensed protein and gelatin as intact protein sources supplemented with crystalline amino acids, were formulated to contain graded levels of methionine (0.6–22.0%) at a constant dietary cystine level of 3 g kg⁻¹. Each diet was randomly assigned to three aquaria. Growth performance and feed utilization were significantly influenced by the dietary methionine levels ( P  < 0.05). Maximum weight gain, feed intake occurred at 12 g kg⁻¹ dietary methionine ( P  < 0.05). Methionine supplementation improved hepatopancreas and intestine weight, hepatosomatic and intestine index, intestinal γ-glutamyltransferase and creatine kinase activity, Lactobacillus count, Bacillus count, lysozyme activities, lectin potency, sim-immunoglobulin M content, addiment C3,C4 contents and serum total iron-binding capacity and declined Escherichia coli and Aeromonas counts. Quadratic regression analysis of weight gain against dietary methionine levels indicated that the optimal dietary methionine requirement for maximum growth of juvenile Jian carp is 12 g kg⁻¹ of the dry diet in the presence of 3 g kg⁻¹ cystine.     

克氏原螯虾的适宜蛋氨酸需求量

以酪蛋白、明胶、鱼粉、小麦面筋粉和晶体氨基酸为蛋白源配制了6组蛋白质水平为28.25%、能量为16.07 kJ/g的等氮等能的半纯合饲料, 各组蛋氨酸实际含量分别为0.39%、0.53%、0.71%、0.86%、0.98%和1.13%。以初始体质量为(9.80±0.15) g的克氏原螯虾(Proambarus clakii)为试验对象, 每组设4个重复, 每个重复12尾虾。养殖试验于室外网箱(规格为60 cm×60 cm×60 cm)中进行, 饲养周期为56 d。结果表明, 当饲料中蛋氨酸水平由0.39%升高至1.13%时, 克氏原鳌虾的增重率、特定生长率和饲料效率均显著升高(P<0.05)。当蛋氨酸水平为0.86%时, 三者均达到最大值。当蛋氨酸水平进一步升高时, 三者均呈下降趋势。试验各组的成活率为83.33%~91.67%, 但无显著差异(P>0.05)。当蛋氨酸水平为0.86%时, 全虾粗蛋白含量最高, 其显著高于0.39%组(P<0.05)。日粮蛋氨酸水平对全虾的水分、灰分和脂肪含量以及肝胰脏组成和肌肉氨基酸组成均无显著影响(P>0.05)。肌肉粗脂肪含量以蛋氨酸水平0.98%组最低, 其显著低于0.39%组(P<0.05)。饲料中蛋氨酸水平显著影响肠道蛋白酶的活性(P<0.05), 但对脂肪酶和淀粉酶活性均无显著影响(P>0.05)。以增重率为评价指标进行一元二次回归分析, 得出克氏原螯虾的适宜蛋氨酸需求量为0.94%, 占饲料蛋白质的3.36%。本研究通过分析饲料中不同蛋氨酸水平对克氏原螯虾生长、饲料利用、虾体组成、肌肉氨基酸组成和消化酶活性的影响, 确定克氏原螯虾的适宜蛋氨酸需求量, 以期为其人工配合饲料的研制提供基础数据和理论依据。