A balanced amino acid diet improves Diplodus sargus larval quality and reduces nitrogen excretion

Fish larvae present high amino acid requirements due to their high growth rate. Maximizing this growth rate depends on providing a balanced amino acid diet which can fulfil larval amino acid nutritional needs. In this study, two experimental microencapsulated casein diets were tested: one presenting a balanced amino acid profile and another presenting an unbalanced amino acid profile. A control diet, live feed based, was also tested. Trials were performed with larvae from 1 to 25 days after hatching (DAH). Microencapsulated diets were introduced at 8 DAH in co-feeding with live feed and at 15 DAH larvae were fed the microencapsulated diets alone. Results showed a higher survival for the control group (8.6 ± 1.3% versus 4.2 ± 0.6% and 3.2 ± 1.8%) although dry weight and growth were similar in all treatments. The proportion of deformed larvae as well as the ammonia excretion was lower in the group fed a balanced diet than in the unbalanced or control groups (38.3% deformed larvae in control, 30% in larvae fed unbalanced diet and 20% on balanced diet group). Furthermore, larvae fed the microencapsulated diets presented higher docosahexaenoic acid and arachidonic acid levels. This study demonstrates that dietary amino acid profile may play an important role in larval quality. It also shows that balanced microencapsulated diets may improve some of the performance criteria, such as skeletal deformities, compared to live feeds.     

Tyrosine and phenylalanine supplementation on Diplodus sargus larvae: effect on growth and quality

Phenylalanine is the precursor of tyrosine, which is involved in the synthesis of several molecules with key roles in the regulation of metabolism and growth, stress response and pigmentation. In this study, three experimental diets were tested: an amino acid (AA) balanced diet supplemented with phenylalanine, another supplemented with phenylalanine and tyrosine and a non‐supplemented AA balanced diet. Rotifers were enriched with liposomes encapsulating free AA in order to obtain a balanced AA profile. The experimental diets resulted in similar larval survival, growth, enzyme activities of AA catabolism and nitrogen excretion in all treatments. High levels of skeletal deformities were registered and significant differences were found between the control and the phenylalanine treatment for the percentage of vertebral compressions in the trunk region of the vertebral column (30% in the control and 5% in the phenylalanine group). A significantly higher survival to a temperature stress test was found for larvae fed the diet supplemented with phenylalanine and tyrosine. The results suggest that supplementation of phenylalanine/tyrosine in fish diets may be useful in order to reduce skeletal deformities and mortalities caused by stress. The present study confirms that AA requirements may be sufficient for covering growth and survival but insufficient to cover other metabolic processes.     

Development of deformities at the vertebral column in Diplodus sargus (L., 1758) early larval stages

One of the bottleneck problems of Diplodus sargus farming is a high incidence of skeletal deformities at the vertebral column. In this study, the pattern of vertebral deformities were determined in three different larval batches from 2 to 30 days after hatching (DAH). During this period, 60 larvae per spawn were observed at 2, 8, 13, 15, 18, 21, 23, 25, 27 and 30 DAH and the different types and frequency of vertebral column malformations were registered. Deformities started from 8 to 13 DAH, when the percentage of deformed larvae rose from approximately 5% to 40%. At 15 DAH, skeletal malformations had frequencies up to 80% of the observed larvae. Serious malformations such as kyphosis, scoliosis and lordosis were observed at 18 DAH but seldom in percentages higher than 15%. Vertebral fusions and compressions especially affected the preurostyle region. Abnormal shape vertebrae were more frequent between vertebrae 15 and 21. Other malformations observed were hypertrophic vertebrae, more common in the trunk and caudal regions, reaching percentages higher than 50% in the former. This study has useful information concerning skeletal malformations at the vertebral column of D. sargus larvae, as it identifies the main deformities observed and the ages of highest incidence.     

Combined effects of rearing density and tank colour on the growth and welfare of juvenile white sea bream Diplodus sargus L. in a recirculating water system

Appropriate rearing conditions for successful farming of white sea bream Diplodus sargus L. have not yet been studied in depth, while one of the major problems is the species increased aggressiveness. Given the known effect of density and background colour on fish growth, welfare and social behaviour, the present study aimed to investigate whether the two factors combined could favour D. sargus performance. Juveniles (17.37±0.06 g) were reared in white, light blue and black tanks under low (7 fish tank⁻¹ or 1.96 kg m⁻³) and high (28 fish tank⁻¹ or 7.79 kg m⁻³) density for 87 days. Water quality was not affected by experimental treatments. The best overall performance (growth, food utilization, body protein content, liver fatty acids) was achieved under low density and white or light blue tanks. Increased incidence of social interactions was indicated in fish under high density or when reared in light blue and black tanks. The present results clearly suggested that the use of black tanks should be avoided. On the other hand, stocking D. sargus at a density of up to 7.79 kg m⁻³ may be feasible because productivity was greater even if growth was slower. In this case, however, the use of white tanks is highly recommended.     

Effects of rearing density on growth, brain neurotransmitters and liver fatty acid composition of juvenile white sea bream Diplodus sargus L.

White sea bream Diplodus sargus L. is a fish species that develops dominance hierarchies and aggressive behaviour against its conspecifics. On the other hand, stocking density is known to affect social interactions, while an appropriate density for D. sargus efficient farming remains to be elucidated. For this purpose, juvenile D. sargus (14.3 g) were reared in 88.4 L tanks, for 10 weeks, under six rearing densities (10, 15, 20, 25, 30 and 35 fish tank^?1). Water quality was not affected by rearing density. Best growth, in terms of final weight, specific growth rate, weight variation and food utilization, was achieved at 10 fish tank^?1. At this treatment the lowest body water content, hepatosomatic and splenosomatic indices, higher body and liver lipid content were also observed. Brain neurotransmitter results indicated increased dopaminergic activity in populations held at higher rearing densities, while serotonergic activity was not affected. Moreover, no significant differences were detected for liver fatty acids. Results of the present study, compared with previously reported data, suggest that, within the range tested, the lowest realistic rearing density for juvenile white sea bream would be 10 fish tank^?1. Higher rearing densities led to decreased growth, which seemed to be related to changes in intraspecific competition and social behaviour.     

Dietary supplementation of mannan oligosaccharide on white sea bream (Diplodus sargus L.) larvae: effects on development,gut morphology and salinity tolerance

The influence of dietary mannan oligosaccharide (MOS) on the development, gut integrity and quality (in respect of stamina and survivability) of white sea bream Diplodus sargus L. larvae was investigated. White sea bream larvae were held under appropriate rearing conditions and fed Artemia, enriched by A1 DHA Selco^? with the addition or absence of MOS (Bio‐Mos®). The results indicated that larval growth performance and survivability were not affected by the MOS supplementation. Light microscopy revealed that MOS supplementation significantly improved the intestinal morphology by increasing the villi surface area by over 12%. Transmission electron microscopy revealed that MOS supplementation increased the microvilli length by 26% compared with the control. Salinity challenge experiments showed that MOS significantly increased larval stamina and survival in both 0 and 60 mg L^?1 salinity water by 13% and 22.9% respectively. These improvements in the larval quality at the early stages of fish development are important for the efficiency of intensive hatchery production.     

Early weaning in meagre Argyrosomus regius: Effects on growth,survival, digestion and skeletal deformities

Meagre Argyrosomus regius is considered a new species for the diversification of finfish aquaculture in the Mediterranean. Several bottlenecks have been identified by producers, and among them, the necessity to establish early weaning protocols to reduce production costs. In this study, two experiments were carried out with meagre larvae from 2 to 35 days post hatch (dph) using different weaning strategies, including the early introduction of artificial diets and the reduction of Artemia metanauplii to half of the normal amounts. A high frequency of cannibalism and high variability in growth rate and survival were obtained in one of the trials and several changes were introduced (reduction of light intensity, higher frequency of food distribution) in the second trial to increase the survival rate. In both trials, weaning started before the complete morphological and functional development of the stomach; thus, pancreatic enzymes, mainly trypsin and lipase tended to be more active in early weaned larvae compared to the control groups. Early weaning delayed the development of the stomach formation and secretion of acid proteases, which may explain the lower growth rates observed in our study. The effect of weaning on skeletal development was also studied and in this sense the results obtained showed no major influence of the early weaning on the incidence of skeletal deformities. Weaning of meagre larvae can be performed as early as 12 dph, but important aspects such as avoiding cannibalism and co‐feeding live prey and artificial diets for at least 5 days were recommended.     

Dietary requirements of rainbow trout for tryptophan,lysine and arginine determined by growth and biochemical measurements

Three separate studies were performed to determine the dietary requirements of rainbow troutSalmo gairdneri for tryptophan (Trp), lysine (Lys) and arginine (Arg) from both growth and biochemical data. The growth studies were carried out over a 12 week period. From graphical plots of % mean weight gain against % amino acid in diet the following requirement values were obtained, Trp 0.25% diet (0.4% dietary crude protein); Lys 1.9% diet (4.3% dietary protein); and Arg 1.6–1.8% diet (3.6–4% dietary protein). Plasma and liver amino acid concentrations measured 20h after feeding did not prove useful for determination of requirement values. Hepatic activities of Trp pyrrolase (TP), Lys ketoglutarate reductase (LKGR) and arginase were not significantly affected by varying levels of Trp, Lys and Arg respectively in the diet. TP has a cytosolic location and a Km of 0.2 mM for Trp; LKGR is mitochondrial and the Km for Lys is 7.3 mM; arginase is also mitochondrial and has a Km of 4.9 mM for arginine. Measurements of expired¹⁴CO₂, after injection of a tracer dose of¹⁴C amino acid, did allow estimates of requirement levels to be made. The values obtained from the oxidation studies reinforced the values obtained from the growth data but were not precise enough to justify using this method on its own.     

饲料中补充晶体或微囊赖氨酸对草鱼生长和血浆总游离氨基酸的影响

为考察饲料中补充晶体或微囊赖氨酸对草鱼生长性能的影响,配制了豆粕含量为23%(高豆粕组),15%(低豆粕组)的两种实用饲料,在低豆粕饲料中补充晶体赖氨酸或微囊赖氨酸,使赖氨酸达到与高豆粕组一致的水平,共4个处理组,即高豆粕组、低豆粕组、低豆粕+晶体赖氨酸(晶体赖氨酸组)、低豆粕+微囊赖氨酸(微囊赖氨酸组),每处理设3个平行。饲养平均体重为(49.0±2.0)g的草鱼8周。结果表明,各组鱼体增重率分别为279.3%、239.7%、245.6%、277.5%,饲料系数为1.62、1.88、1.85、1.62。与低豆粕组相比,添加晶体赖氨酸对草鱼生长无改善(P>0.05),而添加微囊赖氨酸则提高草鱼增重率15.8%(P<0.05),降低饲料系数0.24(P<0.05),在增重率与饲料系数方面达到与高豆粕组基本一致的水平(P>0.05)。对草鱼摄食上述4种饲料0、1、2、3、4、5h后的血浆总游离氨基酸浓度测定结果表明,添加微囊赖氨酸血浆总游离氨基酸的变化趋势与高豆粕组、低豆粕组一致,即在饲后3h达到高峰,而添加晶体赖氨酸使血浆总游离氨基酸的吸收峰值提前。晶体赖氨酸经微囊化后,其水中溶失率显著降低(P<0.05),仅...     

饲料中添加螺旋藻对凡纳滨对虾生长、体组分的影响

系统研究了饲料中添加0～5％不同水平的螺旋藻对凡纳滨对虾生长性能与体生化组成的影响。结果表明：（1）螺旋藻能促进对虾生长,提高饲料的消化利用率,以0．8％、1．5％螺旋藻添加组凡纳滨对虾生长性能较好,试验中期、末期增重率分别达到926．10％、959．78％和4382％、4353．3％,与对照组相比,虾体增重率分别提高2．82％、6．56％和3．45％、2．77％。结合饲料利用、虾体生化组分分析结果表明,饲料中添加0．8％水平螺旋藻为最佳。凡纳滨对虾肝体指数（HSI）随螺旋藻添加量的增加呈现下降趋势。（2）在1％螺旋藻添加范围内,虾体EPA含量内（Y）与螺旋藻添加量（X）呈现良好的线性关系（YEPA=2．4275X＋4．5975,R0=0．9611）,在0．8％范围内螺旋藻,虾体中DHA、ARA的含量与螺旋藻添加量呈显著线性相关（yDHA=4．668X＋5．6545,R^2=0．9631;YARA=105．58X＋0．3241,R^2=0．9749）。（3）从虾体DHA、EPA和ARA含量分析,0．5％大蒜添加量与5％螺旋藻添加量的对虾体脂肪酸改善效果相当。     

Effects of two culturing techniques on the growth, survival and larval quality of Dentex dentex Linnaeus, 1758

Common dentex larvae were reared using two culturing techniques, mesocosms and intensive rearing, to determine the principal culture parameters involved in the differences observed in growth, skeletal deformations and survival between the two rearing techniques. In growth, only dry weight of larvae of 40 days post‐hatching (dph) from mesocosms was significantly higher than larvae from intensive rearing. Significant differences were observed in survival at 40 dph (6.58% in mesocosms and 1.58% in intensive rearing) and in the incidence of skeletal deformations, both for percentage of deformed larvae and for some deformation types such as those related to vertebral column and to the caudal complex. Initial larval density and initial prey density and quality are the factors suspected to affect growth and survival performance, while skeletal deformities might also be affected by tank hydrodynamics.     

Effect of dietary protein and lipid levels on growth and feed utilization of white sea bream (Diplodus sargus) juveniles

In this study, two growth trials were conducted to evaluate the effect of dietary protein and lipid levels on growth and feed utilization of white sea bream (Diplodus sargus) juveniles. For the first trial, five diets were formulated to contain 120 g kg^?1 lipid and increasing levels of protein, ranging from 400 to 600 g kg^?1. Two additional diets were formulated with 400 and 600 g kg^?1 protein and 180 g kg^?1 lipids. The diets were fed to apparent visual satiety to duplicate groups of fish with a mean weight of 1.5 g for 10 weeks. For the second growth trial, four diets were formulated to contain 120 g kg^?1 lipid and 380–520 g kg^?1 protein. Two additional diets were formulated with 380 and 520 g kg^?1 protein and 180 g kg^?1 lipids. The diets were fed to apparent visual satiety to triplicate groups of fish with a mean weight of 41 g for 12 weeks. At the end of both trials, there were no growth differences among groups independent of the dietary protein content. In the first trial, growth was negatively correlated to dietary lipid levels. No significant differences of feed intake were detected among groups in both trials, but a direct correlation between feed efficiency and dietary protein level was observed. Protein efficiency ratio and nitrogen (N) retention (% N intake) significantly decreased with the increase of dietary protein levels. In both trials, energy retention (% energy intake) was highest in groups fed on diets with the highest protein‐to‐energy (P/E) ratio. At the end of both trials, no significant differences in whole‐body composition were observed among groups. Specific activity of enzymes involved in amino acid catabolism [aspartate aminotransferase (AST), alanine aminotransferase (ALT) and glutamate dehydrogenase (GDH)] showed no significant differences with dietary protein level in both trials. Nevertheless, in the first trial, a significantly lower GDH activity was observed in fish fed with higher dietary lipid levels. No differences were found for specific activity of the lipogenic enzymes, fatty aid synthetase and glucose‐6‐phosphate dehydrogenase, in the second trial. Results of this study indicate that a diet with a protein level of 380–420 g kg^?1 and a P/E ratio of 20 g protein MJ^?1 satisfies the growth requirements of D. sargus juveniles. Also, within the range tested, no evidence of protein sparing by dietary lipids seems to occur.     

Effect of dietary lysine and genetics on growth and indices of lysine catabolism in rainbow trout (Oncorhynchus mykiss)

The level of the essential amino acid lysine is of concern in trout feed. The objective of this study was to investigate the response of different families of fish to lysine‐deficient (LD) versus lysine‐adequate (LA) soy protein‐containing diets. For each treatment combination, there were five replicates. As expected, feed efficiency (p < .0001) and thermal growth coefficient (TGC, p < .0001) were improved in fish fed the LA compared to the LD diet. Hepatosomatic index (HSI, p < .01) and whole‐body lipid content (p < .01) were higher for fish consuming the LD compared to the LA diet. There was no effect (p > .05) of diet on hepatic lysine α‐ketoglutarate reductase (LKR) activity, LKR mRNA abundance or lysine oxidation. There was a family effect on feed efficiency (p < .0001), TGC (p < .0001) and condition factor (p < .05) and there was a trend for differences in oxygen consumption (p < .07) across families while consuming the LD diet; however, there was no effect on ammonia excretion, HSI, lipid content, efficiency of nitrogen or lysine retention or indices of lysine catabolism. One family, in particular, had more favourable feed efficiency and thermal growth coefficient when fed the LD diet, indicating that it may possess an enhanced genetic potential for performance when consuming LD, soybean meal‐containing diets.     

Differences in the biochemical compositions of two dietary jellyfish species and their effects on the growth and survival of Ibacus novemdentatus phyllosomas

Phyllosomas (planktonic larvae) of slipper lobsters cling onto and feed on jellyfish under both natural and laboratory conditions. Phyllosomas of Ibacus novemdentatus are capable of feeding on various jellyfish species including venomous stingers; however, the range of jellyfish species capable of supporting the growth and survival of phyllosomas is unknown. Seventeen (12 for the first and five for the second trials) and 18 (13 for the first and five for the second trials) phyllosomas were fed exclusively on the jellyfish Aurelia aurita and Chrysaora pacifica, respectively. Aurelia aurita‐fed phyllosomas metamorphosed into the nisto stage (postbenthic larvae) ～54 days after hatching, whereas C. pacifica‐fed phyllosomas did not. Major nutritional compositions such as amino acids, fatty acids and minerals were compared between the two jellyfish species. The proportion of each major nutritional component was not significantly different between the two jellyfish species, suggesting that C. pacifica was not nutritionally inferior to A. aurita. Therefore, the observation that the C. pacifica‐fed phyllosomas did not metamorphose into the nisto stage was not because of major nutritional compositions but due to other factors such as the lack or excess of other minor nutrients, or the species‐specific texture of the jellyfish.     

Short- and long-term differences in growth, feed conversion efficiency and deformities in juvenile Atlantic cod (Gadus morhua) startfed on rotifers or zooplankton

Growth, feed conversion efficiency and frequencies of skeletal deformities were studied in juvenile Atlantic cod (Gadus morhua) that had been startfed on either rotifers (rotifer group) or zooplankton (zooplankton group). After metamorphosis, the fish were reared at four constant temperatures (7, 10, 13, 16°C) or moved successively from 16 to 13 and 10°C (T‐step, average 13.2°C). The zooplankton group had a consistently higher growth rate at all the temperatures studied. Further, the zooplankton group had higher food intake (20%) and higher feed conversion ratio (1.65 vs. 1.31). In addition, a significantly higher incidence of skeletal deformities was found in the rotifer group (14.2%) compared with the zooplankton group (4.1%). After termination of the laboratory study, the fish were reared in sea pens under ambient conditions for 17 months. Final weights of the zooplankton group were consistently larger (between 12% and 14% larger depending on original temperature groups). To verify the growth results, we conducted a follow‐up study where a single egg group was divided into two parts and fed either on rotifers or zooplankton. This study indicated similar growth differences as found in the first study. Overall, our data suggest that different startfeeding diets may be important for long‐term growth, incidence of deformities and quality of juvenile cod. The use of zooplankton can greatly improve long‐term growth and quality of cod juveniles. The study also highlights the advantage of using elevated temperatures in the juvenile phase as this will lead to significantly higher final weights in the adult stage.     

Amino acid absorption and protein synthesis responses of turbot Scophthalmus maximus to lysine and leucine in free,dipeptide and tripeptide forms

The study aimed to investigate the effects of crystalline Lys and Leu, Lys‐Leu dipeptide and Lys‐Leu‐Lys/Leu‐Lys‐Leu tripeptide, on growth, postprandial Lys and Leu concentrations, gene expression of peptide and amino acid (AA) transporters and related gene expression of protein synthesis pathway in turbot. Three diets (CAA, Di and Tri) contained Lys and Leu as free (Lys and Leu), dipeptide (Lys‐Leu) and tripeptide (Lys‐Leu‐Lys/Leu‐Lys‐Leu) forms, respectively. Improved growth was observed in the Di group compared with the CAA group. For peptide and AAs transporters, PepT1, B⁰AT1 and y⁺LAT2 mRNA levels were affected in proximal intestine by dietary treatments. Free Lys and Leu concentrations in the CAA group were significantly higher than that of the Di and Tri groups at 6 hr postfeeding in serum and at 2, 6 and 24 hr postfeeding in muscle. For protein synthesis pathway in muscle, Akt2, TOR and S6k1 gene expression were the highest in the Di group and the lowest in the CAA group, whereas MuRF1 relative expression was the highest in the Tri group. In conclusion, dietary Lys‐Leu dipeptide was utilized more efficiently than free Lys and Leu or Lys‐Leu‐Lys/Leu‐Lys‐Leu tripeptide for turbot by regulating AAs transport, postprandial AAs concentration and the synthesis of muscle proteins.     

饲料中添加晶体或包膜氨基酸对异育银鲫生长和血清游离氨基酸水平的影响

进行了二个试验考察饲料中添加晶体或包膜氨基酸对异育银鲫生长和血清游离氨基酸水平的影响。试验Ⅰ设计了鱼粉含量为18%和9%的两种基础饲料(分别为高鱼粉对照组、低鱼粉对照组),在低鱼粉对照组中分别添加晶体形式、环糊精包膜、淀粉包膜的赖氨酸0.23%、蛋氯酸0.09%,饲养平均体重2.48 g的异育银鲫鱼种6周。结果表明,高鱼粉对照组、低鱼粉对照组、晶体氨基酸组、环糊精包膜氨基酸组、淀粉包膜氨基酸组的鱼体增重率分别为214.3%、169.8%、173.3%、204.7%、203.2%,与低鱼粉对照组相比,添加晶体氨基酸对异育银鲫的生长无改善(P>0.10),但添加环糊精包膜或淀粉包膜氨基酸提高了鱼体增重率20.5%、19.7%(P<0.05),饲料系数下降0.40、0.39(P<0.05)。试验Ⅱ在鱼粉含量为6%的基础饲料分别添加晶体形式、环糊精包膜、淀粉包膜的赖氨酸0.20%、蛋氨酸0.08%,在异育银鲫成鱼(平均体重220 g)摄食上述4种饲料后1、3、5、12h,尾静脉采血测定血清游离氨基酸浓度,结果表明,添加晶体氨基酸使血清游离氨基酸的吸收峰值提前,相对于晶体氨基酸而言,环糊精包膜或淀粉包膜氨基酸则使血清游离氨基酸的吸收峰值出现不同程度的延迟。上述研究表明,晶体氨基酸经环糊精、淀粉包膜处理后,其在消化道的吸收速度减缓,可利用性显著提高。     

Effect of dietary l‐lysine levels on growth,feed conversion,lysine retention efficiency and haematological indices of Heteropneustes fossilis (Bloch) fry

Effect of varying dietary lysine levels on growth, feed conversion, nutrient retention, lysine retention efficiency and haematological indices of Heteropneustes fossilis fry (2.97 ± 0.11 cm; 4.78 ± 0.31 g) was studied by conducting a 12‐week feeding trial. Isonitrogenous (450 g kg^?1 CP) and isocaloric (17.97 kJ g^?1 GE) amino acid test diets with graded concentrations of l ‐lysine (18, 20, 22, 24, 26, 28 g kg^?1 dry diet) were fed to triplicate groups of fish to apparent satiation twice daily at 17 and 17:30 h. Maximum thermal growth coefficient (TGC, 0.82), best feed conversion ratio (FCR, 1.28) highest protein retention efficiency (PRE, 36%), energy retention efficiency (ERE, 79%) and lysine retention efficiency (LRE, 75%) were noted at 24 g kg^?1 lysine of dry diet. Body protein was also found to be in line with growth data and peaked at 24 g kg^?1 lysine of dry diet. Similarly, superior somatic and haematological indices were exhibited by the groups fed dietary lysine at 24 g kg^?1 of the dry diet. However, exponential analysis of dietary lysine intake against TGC, lysine retention and protein retention indicated that inclusion of dietary lysine in the range of 13.24–14.14 g kg^?1 dry diet, corresponding to 29.42–31.42 g kg^?1 dietary protein, is essential for faster growth of this fish.     

Effect of dietary protein reduction with lysine and methionnine supplementation on growth performance,body composition and total ammonia nitrogen excretion of juvenile grass carp,Ctenopharyngodon idella

A 63‐day growth trial was undertaken to estimate the effects of supplemented lysine and methionine with different dietary protein levels on growth performance and feed utilization in Grass Carp (Ctenopharyngodon idella). Six plant‐based practical diets were prepared, and 32CP, 30CP and 28CP diets were formulated to contain 320 g kg^?1, 300 g kg^?1 and 280 g kg^?1 crude protein without lysine and methionine supplementation. In the supplementary group, lysine and methionine were added to formulate 32AA, 30AA and 28AA diets with 320 g kg^?1, 300 g kg^?1 and 280 g kg^?1 dietary crude protein, respectively, according to the whole body amino acid composition of Grass Carp. In the groups without lysine and methionine supplementation, weight gain (WG, %) and specific growth rate (SGR, % day^?1) of the fish fed 32CP diet were significantly higher than that of fish fed 30CP and 28CP diets, but no significant differences were found between 30CP‐ and 28CP‐diet treatments. WG and SGR of the fish fed 32AA and 30AA diets were significantly higher than that of fish fed 28AA diets, and the performance of grass carp was also significantly improved when fed diets with lysine and methionine supplementation (P < 0.05), and the interaction between dietary protein level and amino acid supplementation was noted between WG and SGR (P < 0.05). Feed intake (FI) was significantly increased with the increase in dietary protein level and the supplementation of lysine and methionine (P < 0.05), but feed conversion ratio (FCR) showed a significant decreasing trend (P < 0.05). Two days after total ammonia nitrogen (TAN) concentration test, the values of TAN discharged by the fish 8 h after feeding were 207.1, 187.5, 170.6, 157.3, 141.3 and 128.9 mg kg^?1 body weight for fish fed 32CP, 32AA, 30CP, 30AA, 28CP and 28AA diets, respectively. TAN excretion by grass carp was reduced in plant‐based practical diets with the increase in dietary protein level and the supplementation of lysine and methionine (P < 0.05). The results indicated that lysine and methionine supplementation to the plant protein sources‐based practical diets can improve growth performance and feed utilization of grass carp, and the dietary crude protein can be reduced from 320 g kg^?1 to 300 g kg^?1 through balancing amino acids profile. The positive effect was not observed at 280 g kg^?1 crude protein level.