介绍

对于鱼食中的鱼粉替代性的研究课题，许多科研人员都做过研究。尤其对于虹鳟鱼的研究，一些富含蛋白质的植物像大豆，玉米麸粉，豆粉和菜籽粉等可能部分，甚至完全替代现有的鱼粉。多宝鱼对于氨基酸需求的数量至今未知，但是kaushik 曾经尝试评估出具体的氨基酸。

鱼食中的蛋白质节约。主要是整合其他的非蛋白质物质，通过其他蛋白质来源取代鱼粉。对于多宝鱼，蛋白质节约通过脂肪或者碳水化合物等物质是不太可能。

目前的研究很少涉及植物蛋白质的使用。玉米麸粉是富含担保质，纤维素含量低，同时富含维生素B 和E 的物质，最佳的是不含抗营养因子。然而，玉米麸粉缺乏谷物的赖氨酸。在鲑鳟鱼中，这是赖氨酸的补充。

基于对多宝鱼的研究，希望达到以下的目的：1、通过喂食不同含量的玉米麸粉鱼食来测量消化吸收率以及氨基酸的存在情况；2、逐步地用含有玉米麸粉的鱼食替代鱼粉，来观察多宝鱼的成长情况；3、评估玉米麸粉在胆固醇，甘油三酸脂，甲状腺激素，背肌和游离氨基酸的浓度方面效用。

In the context of research of the substitution of fish meal in diets of fish, numerous1992; Gomes et al., 1995; Kaushik et al., 1995; Burel et al., 1996b, 1998a have shown,.in particular with rainbow trout ŽOncorhynchus mykiss., that it is possible to partially oreven fully replace fish meal by plant protein sources such as soybean, corn gluten meal

CGM , lupin flour, rapeseed meal, etc. Even in marine fish, the interest of plant.et al., 1995; Nengas et al., 1996; Burel et al., 1998b ..

The turbot Psetta maxima.

1980; Cacerez-Martinez, 1984; Guillaume et al., 1991; Danielssen and Hjertnes, 1993 ..Data on the quantitative essential amino acid requirements of turbot is www.steelbee.net not available butKaushik, 1995 . An attempt has recently been made to estimate the amino acid.

protein economy in fish feed: protein sparing through incorporation of non-protein1994 and replacement of fish meal by other protein sources. In turbot, protein sparing.by fats or carbohydrates does not seem to hold much promise. Turbot do not appear to

Cacerez-Martinez et al., 1984; Andersen and Alsted, 1993; Danielssen and Hjertnes,1993 ..To our knowledge, so far, very few studies have dealt with the use of plant proteinBurel et al., 1998b . Corn gluten meal has a high protein level, is low in fiber, rich in.vitamins B and E and is known to contain no antinutritional factors. CGM is howeverdeficient of the amino acid lysine. In salmonids, a supplementation with lysine is.

The objectives of the present study conducted with turbot were 1 to measure .digestibility and amino acid availability of experimental diets containing graded levelsof CGM, 2 to evaluate growth performance of turbot fed diets in which fish meal was .gradually replaced by CGM, 3 to evaluate the effects of CGM incorporation on plasma .cholesterol, triglyceride and thyroid hormone concentrations and plasma and dorsalmuscle free amino acid concentrations.

实验的材料和方法

2.1、用于实验的鱼食

五种用于实验的鱼食制作好。他们含有不同的玉米麸粉。第一种是不含玉米麸粉。第二到第五种鱼食分别含有20%，40% 和57% 玉米麸粉， 跟鱼粉中的蛋白质一致。在第四和第五种鱼食中没有鱼粉，只是增加了不同量的两种氨基酸和左型精氨酸。鱼食具体的原料和化学构成可以参考图1，对于相应的氨基酸含量可以参考图2。

Five experimental diets were formulated. They contained a gradient of CGM in replacement of original fish meal. Diet 1 contained no CGM and served as control. Diets

2 to 5 contained 20, 40 and 57% of CGM replacing equal amounts of protein from fishmeal. Diets 4 and 5 had no fish meal and were supplemented with differing amounts of two amino acids, L-arginine and 1983 , was added in each diet at a level of 150 ppm. The ingredient and chemical. compositions of diets are presented in Table 1 with the corresponding amino acid compositions in Table 2.

图一

鱼食的原料和化学构成：

1 2 3 4 5

原料（%）

鱼粉 52 31 14 ---- ---

玉米麸粉 --- 20 40 57 57

可溶鱼蛋白质浓度 8 8 8 8 8

鱼油 3 4.5 5.5 6.5 6.5

谷氨酸 --- 2.5 2.1 1.3 ---

L-赖氨酸 --- --- 0.4 1 1.8

左型精氨酸 --- --- --- 0.2 0.7

次粉 5 5 5 5 5

豆类 29.99 26.99 21.99 15.99 15.99

矿物混合物 1 1 1 1 1

维他命混合物 1 1 1 1 1

磷酸二钙 --- --- 1 1 1

肌苷 0.01 0.01 0.01 0.01 0.01

大致构成

干物重 % 94.1 93.22 93.4 92.98 93.9

原蛋白质 49 49.46 51.81 52.77 53.53

原脂肪 11.91 11.77 11.93 12.21 11.80

淀粉 15.11 16.20 15.89 15.66 16.17

灰分 11.16 7.96 6.11 5.62 5.58

磷 1.6 1.15 0.89 1.00 0.97

净能量 千焦 20.76 21.29 21.81 22.52 22.43

易消化的蛋白质 46.1 43.8 41 39.4 39.2

易消耗的能量 17.2 16.2 15.3 14.8 15.3

比率 26.9 27.0 26.8 26.7 25.7

图二

氨基酸的构成

1 2 3 4 5

精氨酸 5.9 5.19 4.42 4.22 4.90

组氨酸 2.47 2.24 2.08 2.01 1.96

异亮氨酸 4.08 3.96 3.75 3.56 3.66

白氨酸 7.31 9.56 11.93 13.24 13.38

赖氨酸 7.63 5.72 4.59 4.47 5.48

蛋氨酸 3.14 3.15 3.26 3.18 3.20

苯基丙氨酸 6.96 7.56 8.55 8.77 8.99

苏氨酸 4.18 3.74 3.55 3.33 3.29

色氨酸 1.12 0.93 0.73 0.61 0.60

氨酸 4.98 4.77 4.48 4.32 4.36

必须的氨基酸

冬氨酸 9.45 8.24 7.22 6.52 6.36

谷氨酸 13.98 20.95 22.29 22.48 19.55

丝氨酸 4.00 4.10 4.63 4.68 4.6

氨基乙酸 6.31 5.3 4.34 3.78 3.64

丙氨酸 6.12 6.59 7.24 7.58 7.63

脯氨酸 --- --- --- --- ---

2.2 吸收消化率的测量

佩林测量仪是用来测量吸收消化率的工具。透过直径为4.5毫米的物件作为指示标志。为了研究鱼排泄物的连续性和完整性，2%的海藻酸钠用在鱼食中。Cr O . Thirty turbot mean body weight: 130.8."1.2 g were allotted to cylindroconi-.Žcal tanks, each of which was equipped with a flat-bottomed large-mesh basket. Fish

30条多宝鱼总重达130.8磅。其中1.2克的鱼放进了圆锥形的容器中，每个容器有着圆的底部和。鱼根据实验的条件进行饲养，每个鱼食都是15天的周期。同时，鱼每天喂一次。鱼排泄物的样本每天早上收集一次。同时将排泄物进行冷冻。鱼排泄物冷冻变干后，将从排泄物中分析蛋白质，氨基酸，淀粉，磷和能量物质。

试验中的鱼食中氨基酸的构成计算公式如下：

2.3 鱼的生长情况研究

养鱼的水温控制在17度。71条多宝鱼最初总重为65.6克。三群鱼每天收工喂两次。每天喂养一次。为了追踪鱼的生长和饲养状况，每群鱼每三周称一次重量。

在鱼成长之初，15条鱼作为样本。被养在y208c 的容器内从而来分析整个鱼的营养构成。20条原来养在同一个容器的鱼通过其肝脏和消化系统来计算肝指数和内脏器官的指标。用于分析的样本通过液态氮冷冻起来，存放在Y808C。

在研究鱼成长的过程中，喂食1，2，3 的鱼群的生长情况较差。根据进一步分析的结果对三个鱼群生长情况进行研究。通过解剖得到的鱼的肝脏和内脏要进行称重。喂食后的16个小时鱼的血浆通过离心法分离的物质用来分析甘油三酸脂，胆固醇，甲状腺激素和游离的氨基酸。从其中20条鱼的12条中分离出背肌样本在液态氮条件下冷藏并储存在Y808C。

2.4 研究分析方法

样本的分析过程如下：对于需要干燥的物质，通过在摄氏1058度的炉子干燥24小时。对于粉类物质在550.8度干燥12小时。用杜氏法分析原蛋白。氮分析方法。菲瑟恩工具，对于原脂肪采用二氯甲烷提取方法。同时还有淀粉糖葡萄糖及氧化酶法。采用二甲亚砜的方法分析淀粉的可溶性。通过使用粉类物质，磷中的磷酸盐可以显现。当高氯酸被消化时可以决定鱼食和分泌物中的氧化铬的含量。

血液中的胆固醇和甘油三酸脂总浓度是编号55241胰蛋白的浓度。三碘甲状腺氨酸和甲状腺素的浓度用放射性免疫方法测定。在分离之前，对于来自鱼食和鱼分泌物的氨基酸分析，采用氯酸和异硫氰酸盐试剂的方法来进行。对于游离氨基酸，来自同一个容器三条鱼的肌肉组织被冷冻。通过氯酸把游离氨基酸分离出来。用上述的办法可以分析血液中的游离氨基酸。

2.5 数据分析

所有的数据都是通过对于各种变化的分析得到的。纽曼-科伊尔斯检验方法用来比较各种方法。

were adapted to the experimental conditions and to each experimental diet over a total period of 15 days. Fish were fed to satiety once a day and faecal samples were collected each treatment, faecal samples were collected once a day each morning over 48C for 20 min and frozen daily.at y208C. After freeze drying, the faeces were analysed for chromic oxide, protein,amino acids, starch, phosphorus and energy.

The ADC of the experimental diets was calculated as follows:% Cr O in Diet % Nutrient or Energy in Faeces = /ADC %. s 100y 100 % Cr O in Faeces % Nutrient or Energy in Diet

2.3. Growth study

de Brest at a constant water temperature of 17. " 18C in a flow through system for a period of 9 weeks. 71 turbot having a mean initial body weight of 65.6 "0.1 g were

y1.. A

12r12 h lightrdark cycle was adopted. Triplicate groups were fed by hand twice a day

one meal was given per day. Each group was weighed every 3 weeks to follow growth and feed utilisation.

At the beginning of the growth study, 15 fish were sampled and stored at y208C for analyses of whole body composition. Twenty fish from the same initial pool were also

withdrawn to weigh the liver and the digestive tract for calculating hepatosomatic index HSI and viscerosomatic index VSI . Samples for analyses were frozen in liquid nitrogen and stored at y808C.

During the growth study, one each of the triplicate groups fed diets 1, 2 and 3 were found to have poor feeding behaviour and growth performances. Data for these were not included and all further analyses for these three treatment groups were based on data

withdrawn for analyses. Dissected, the liver and viscera were weighed. Twenty fish from syringes after 16 hours after the last meal. Plasma was collected after centrifugation Ž1200 g, 8 min at 58C and stored frozen at.y188C as separate aliquots for analyses of triglyceride, cholesterol, thyroid hormones and free amino acids. A sample of dorsal muscle was taken from 12 of these 20 fish and frozen in liquid nitrogen and stored aty808C.

2.4. Analytical methods

Analyses of samples were made as follows: dry matter after desiccation in an oven 1058C for 24 h , ash incineration at 550. 8C for 12 h , crude protein Dumas, nitrogen.analyser, Fison instrument, N =6.25 , crude fat dichloromethane extraction by Soxlhet.method , starch gluco amylase glucose oxydase method by kit system Boehringer no..207748, Mannheim, Germany, after solubilization of starch by dimethyl sulfoxide andHCl , phosphorus ortho phosphate was determined photometrically after ashing using.the vanado-molybdate method and gross energy IKA Adiabatic Calorimeter C4000A .. .The chromic oxide in diets and faeces was determined after perchloric acid digestionŽBolin et al., 1952 ..

Plasma total cholesterol concentrations and plasma triglyceride concentrations were terol and kit Oxoid no. 55241 for triglycerides . Thyroid hormone triiodothyronine and.thyroxine concentrations were determined with a radioimmunoassay technique RIA.1995 ..Analyses of amino acids from diets and faeces were made using a procedure with

hydrochloric acid and derivatised with phenyl isothiocyanate reagent before separationby HPLC. For the free amino acids, the muscles of three fish coming from the same tankwere freeze dried and pooled. Free amino acids were extracted with 0.1 N hydrochloricNOVAPAK C18 3.9= 300 mm. Free amino acids of plasma were analysed by Euroly

2.5. Statistical analysis

All data were subjected to one-way analysis of variance to test the effects of s0.05 , the Newman–Keuls test was used to compare the means. All statistical tests were

3. Results

3.1. Nutrient and energy digestibility and amino acid aÕailability

During faecal collection, one major visual observation was the presence of relativelyintact gluten particles in the faecal matter of fish fed diets 3 to 5. Data on ADC arepresented in Table 3. ADC of starch and phosphorus were not statistically differentŽ P )0.05 between diets. ADC of protein and energy decreased with an increase of.CGM incorporation in the diet. ADC of protein was relatively high in comparison withthe other nutrients. Incorporation of CGM led to a very significant decline in ADC ofproteins

declined with incorporation of CGM, reflecting ADC of protein. The availability ofleucine, phenylalanine and tyrosine were lower than that of the ADC of protein. On theother hand, lysine and arginine availability were relatively higher than that of otheressential amino acids. Availability of lysine was in general higher than 90%. For thesetwo amino acids, the availability in diet 5 was higher than those in diet 4 but it was notsignificantly different for arginine.

3.2. Growth performance

Turbot fed diet 3 showed a slightly lower FBW and SGR and the values weresignificantly different from the other groups. When fish meal was totally replaced byCGM, a further significant growth reduction was observed. Supplementation withL-lysine and L-arginine did not alleviate this growth retardation. Best feed efficiencyFE values were observed for fish fed diets containing fish meal. Fish fed diet with 20%.

3.分析结果

3.1 营养和能量消化吸收率和氨基酸含量率

在收集鱼分泌物的过程中，主要去观察喂了3到5类鱼食的鱼分泌物的相对完整的麸粉颗粒的存在性。氨基酸的构成可以参考图三。淀粉和磷中的氨基酸构成在不同的鱼食中的含量是不同的。随着鱼食中的玉米麸粉的含量的增加，蛋白质和能量中的氨基酸含量在减少。比较其他的营养元素，蛋白质中的氨基酸含量比较高。玉米麸粉的增加明显地影响蛋白质中的氨基酸的含量。

跟蛋白质中的氨基酸含量相比，白氨酸，苯基丙氨酸和铬氨酸的含量低。另一方面，跟其他必须的氨基酸种类相比，赖氨酸和精氨酸的含量高。其中赖氨酸的含量高达90%. 针对这两种氨基酸，在第五种鱼食中的氨基酸含量比第四种的含量高。但是这是不同于精氨酸的氨基酸种类。

图三

氨基酸含量的消化吸收系数

氨基酸含量 1 2 3 4 5

蛋白质 94.0"0.0 88.5"0.4 79.1"1.7 73.9"0.1 73.5"0.2

淀粉 77.6"0.1 75.7"0.3 76.1"0.5 73.3"1.7 74.7"0.9rns

磷 71.1"2.6 73.4"1.2 69.5"1.7 63.6"0.6 68.4"1.2rns

能量 82.6"0.1 76.2"0.0 70.2"1.4 66.4"0.3 67.4"0.6

3.2 生长情况

采用第三种鱼食喂养的多宝鱼在FBW和SGR的含量比较低。这个其他的鱼群不一样。当鱼粉完全被玉米麸粉替代后，可以观察鱼的生长减缓。同时增加了赖氨酸和左型精氨酸后还是不能减缓生长滞后。好的鱼食应该还有一定含量的鱼粉。鱼食中含有20%的鱼粉有助于鱼类的生长。

图四

鱼食中的氨基酸的含量

1 2 3 4 5

精氨酸 96.3"0.2

组氨酸

异亮氨酸

白氨酸

赖氨酸

蛋氨酸

苯基丙氨酸

苏氨酸

色氨酸

氨酸

铬氨酸

必须的氨基酸

冬氨酸

谷氨酸

丝氨酸

氨基乙酸

丙氨酸

脯氨酸 --- --- --- --- ---

图五

喂食63天的多宝鱼的生长情况

1 2 3 4 5

IBW 克

FBW 克

SGR %

FE %

PER%

3.3 鱼和背肌的组成部分和营养的保有量

多宝鱼饲养前后的营养构成可以参考图六。 在喂养之初，鱼整个身体的水含量在减少。在实验结束时，主要参考一下的指标：鱼的水含量，肝指数，内脏指数和能量的储存和背肌的含量。

图六

1 2 3 4 5

干性物质 23.01

粉类

蛋白质

脂肪

磷

能量

肝指数

内脏指数

保有量%

干性物质

蛋白质

脂肪

能量

背肌

干性物质

蛋白质

脂肪

干性物质是这通过冷冻变干的物质。喂养不同的鱼食所含的蛋白质是不同的。跟其他的鱼食相比，喂第二类鱼食的鱼的脂肪含量相对高。而喂养第一和五类的鱼食的鱼的脂肪含量最低。对于喂养不同的鱼食的鱼磷元素含量是不同的。对于喂养第五类鱼食的鱼的能量含量相对是低的。肝指数的范围不同，从0.8%到1.2%。肝指数高的鱼的生长状况好。背肌中的脂肪含量是不同的，范围从21.6%到18%。 仅仅喂养了第一种和第五种的鱼食的鱼能量含量不同。在实验期间，多宝鱼中肌肉的脂肪含量是低的，没有明显的不同。

随着在鱼食中增加玉米麸粉了，营养和能量的保有量受影响。可以参考图6. 喂养第一种鱼食的蛋白质保有量可以达到41%。而喂养了第五种鱼食的却降到19.7%。

3.4 胆固醇和甘油三酸脂浓度

胆固醇和甘油三酸脂的浓度如图七所示。当在鱼食中增加了玉米麸粉，胆固醇和甘油三酸脂的浓度将要降低。

3.5 甲状腺激素

甲状腺激素的浓度如图八所示。当在鱼食中增加了玉米麸粉，三碘甲状腺氨酸的浓度将要降低。SGR 和 T3 浓度呈现正比的线性关系。甲状腺T4 浓度成反比关系。随着T3浓度的变化，T3和T4的比率可以反映不同的甲状腺的含量变化。

图八

多宝鱼的甲状腺浓度

1 2 3 4 5

T3ZNGML

T4ZNGML

T3RT

图九

1 2 3 4 5

精氨酸 95.6"11.0

异亮氨酸

白氨酸

赖氨酸

苯基丙氨酸

苏氨酸

色氨酸

氨酸

铬氨酸

胱氨酸

冬氨酸

谷氨酸

丝氨酸

氨基乙酸

丙氨酸

脯氨酸 --- --- --- --- ---

图十

1 2 3 4 5

精氨酸 34.9"5.6

组氨酸

异亮氨酸

白氨酸

赖氨酸

蛋氨酸

苯基丙氨酸

苏氨酸

色氨酸

氨酸

铬氨酸

冬氨酸

谷氨酸

丝氨酸

氨基乙酸

丙氨酸

noted in fish fed diet 5. No significant P ) 0.05 difference was found in the whole.body protein content of fish fed the different experimental diets. Whole body fat content was significantly higher in turbot fed diet 2, with fish fed diet 1 or diet 5 having the lowest fat content. Although whole body phosphorus content of fish varied between treatments, no specific trend was observed. Gross energy content was low in turbot fed diet 5, significantly different Ž P -0.05 from those fed diets 1, 2 and 3. The HSI varied.from 0.8% to 1.2%. HSI values were higher in fish who had the best growth

weight = 6.25 and fat content of dorsal muscle showed some variation and.

varied between 21.6% and 18.0%. Statistical difference was only found between fish fed diet 1 and fish fed diet 5. Muscle fat contents of turbot were low and no significant difference was observed between treatments.

Nutrient and energy retention were affected by an increase in dietary CGM levels Table 6 . Protein retention was high 41.0% in fish fed diet 1 and fell to 19.7% in fish.fed diet 5. The highest value of fat retention was observed in fish that had the best

computed and presented in Fig. 1. Data in Fig. 1a show that irrespective of the IAA concerned, the retention values were low in fish fed diets containing CGM as the total

was however comparable between groups, except for a slight decline in those fed diet 5 for almost all amino acids.

3.4. Plasma cholesterol and triglyceride concentrations

Plasma total cholesterol and triglyceride concentrations are reported in Table 7. Both plasma cholesterol and triglyceride concentrations decreased with increasing levels of

CGM in the diets. The values ranged from 4.39 grturbot fed diet 5 ..

3.5. Thyroid hormones

Plasma thyroid hormone concentrations are presented in Table 8. Triiodothyronine ŽT3 concentrations decreased with an increase of dietary CGM levels. The highest.

performance had low plasma T3 concentrations. A positive linear relationship between SGR and T3 concentrations was observed rs 0.87 . Thyroxine T4 concentrations. varied in the opposite direction. The values appeared to increase when growth rates

3.6 游离的氨基酸

在背肌中，几乎所有的氨基酸的浓度都是降低的。随着玉米麸粉的增加，白氨酸的浓度也随着增加。跟喂养第四类鱼食的相比，在喂食第五类鱼食中发现精氨酸和赖氨酸的浓度偏高。

4.讨论

对于鱼类来讲，蛋白质消化吸收率的范围从75%到95%。包含20%玉米麸粉的鱼食有着强的消化吸收率。这个含有相同比例的玉米麸粉的结果相一致。含有玉米麸粉可以部分取代鱼粉，这个结果令人惊讶。尽管这个可以导致蛋白质的消化吸收率的明显下降。采用含有玉米麸粉的鱼食可以导致低的消化吸收率。用同样的方法研究欧洲的鲈鱼可以得到同样的结果。也就是说氮元素的过滤作用不明显。由于在鱼食中含有藻酸盐，使多宝鱼的分泌物有很大的粘性。在鲑类鱼中，增加藻酸盐可以使鱼的分泌物更容易收集。如果藻酸盐的浓度高于4%就可能影响消化吸收率。

通过研究相关的数据，淀粉的消化吸收率为75%。主要的几个鱼食的组成部分跟鲑鱼中的淀粉的消化吸收率相似。磷元素的含量在不同类别的鱼食含量中都不相同。氨基酸的含量可以反映蛋白质的消化吸收率。到现在为止，在多宝鱼中有关氨基酸的要求或者含量的数据还没有。通过喂食含有玉米麸粉的鱼料，可以增加鱼食的酸性。含有玉米麸粉的鱼食部分取代鱼粉可以证明多宝鱼可以有效地利用透明的氨基酸。相似的研究也在鳟鱼身上进行。采用第一种和第二种鱼食喂养的多宝鱼有着好的成长状况。含有20%的玉米麸粉的鱼食跟不含玉米麸粉的鱼食的鱼的成长情况相似。含有玉米麸粉的鱼食完全取代鱼粉可以延缓30%鱼的成长速度。随着玉米麸粉的含量的增高，消化吸收率在下降。跟鱼粉相比较，由于富含白氨酸和缺乏色氨酸，导致鱼的生长情况较差。采用第一和第二类鱼食喂养次数较高。研究发现跟鳟鱼相比，这些鱼的生长状况较好。蛋白质的氨基酸含量跟FE 和 PER 关系密切。

多宝鱼的全部蛋白质含量没有受到鱼食种类的影响。另一方面，多宝鱼的脂肪含量也是不同的。尽管采用第一和第二类鱼食喂养的多宝鱼有着相似的生长情况，但是采用第二种鱼食喂养的鱼的脂肪含量比采用第一种鱼食喂养的鱼脂肪含量高。然而，跟许多样品不同的是，多宝鱼的脂肪含量是低的。

根据以前的研究结果，采用鱼粉喂养的鱼的蛋白质含量高于40%。 如果鱼食中加入了玉米麸粉，蛋白质和能量的含量会降低。尽管在第五种鱼食中富含精氨酸和赖氨酸，但是这两种氨基酸的含量并没有提高。跟鲤鱼相似，玉米麸粉可以增加蛋氨酸，赖氨酸和苏氨酸的含量。上述的因素导致了IAA的含量的降低。

通过研究发现，鱼食中增加了精氨酸和赖氨酸导致了在鱼肌和血浆中这两种氨基酸浓度的增加。从游离氨基酸和氨基酸的含量可以确定补充EAA可以提高氨基酸的供给和平衡。根据1995年的研究，当增加IAA 在鱼食中，赖氨酸和蛋氨酸在血浆中的浓度增加。鱼肌是保存FAA重要的组织。不幸的是，我们无法使用分析的方法来研究和得到这两种氨基酸在多宝鱼肌的可靠数据。

喂养含有玉米麸粉的鱼食导致在鱼肌和血浆中的白氨酸浓度增加。通过减少异亮氨酸和 氨酸的含量，可以导致血浆中两种氨基酸含量的增加。在随后的研究中，在肝指标上没有差别。

跟喂食鱼粉的相比，喂食含有玉米麸粉的鱼的肝指标相对低。这可能是由于生长的减缓，这也是在多宝鱼身上脂肪转移的结果。在研究替代鱼粉的问题上，喂食富含植物蛋白质的鱼食可以使问题更加严重。不仅跟氨基酸的平衡有关，而且能引起其他的问题。

鱼食中的植物蛋白质对于鱼的可能的次级生理影响很少被研究。随着身体中的脂肪含量的降低，血浆中的随之降低。甘油三酸脂浓度变化可以引起鱼群的脂质转移，从而对生长情况产生不利的影响。植物蛋白质也可以影响胆固醇的浓度。鱼食含有过高的玉米麸粉可以引起血浆中胆固醇的浓度的降低。

根据一些研究人员研究结果，甲状腺激素和它的活动有助于利用脱碘酶进行T3到T4之间的转换。在我们的研究中，玉米麸粉对于甲状腺的浓度的影响没有发现。其中涉及的研究方法和可能的结果将要进一步的被关注。

decreased, but a clear relationship was not observed. The T3rT4 ratio reflecting thyroid

hormone activity varied in accordance with changes in T3 concentrations. Plasma T3r Ž rml, respectively were.significantly lower Ž P -0.05 than in fish from the other groups..

3.6. Free amino acids

In dorsal muscle, we observed a decrease in concentrations of almost all indispens-

the concentration of leucine increased with increasing levels of dietary CGM, whereas

Concentrations of arginine and lysine increased in the muscle of fish fed diet 5 in comparison with fish fed diet 4. While the levels of most non-indispensable amino acids declined with increasing dietary CGM levels, those of serine and proline had a marked Ž

were found only for leucine Ž P -0.05 , which increased with dietary CGM levels..Arginine and lysine were found to be higher in fish fed diet 5 than in fish fed diet 4.

4. Discussion

In fish, protein digestibility is generally high ranging from 75% to 95% Cho andŽ Kaushik, 1990; National Research Council, 1993 . ADC of proteins from fish meal is.

from fishmeal in turbot is comparable to values found in other teleosts. Diet containing 20% of CGM meal had a very good digestibility, in accordance with the results of

about 20% CGM. In contrast, ADC of diets with high levels of plant proteins were very Council, 1993 . It is then surprising that inclusion of CGM in replacement of fish meal. led to a significant decrease in protein digestibility. The low digestibility values recorded CGM used here were rather high or to the method of faeces collection. Spyridakis et al..

Ž1989 , using the same method in a study on digestibility in European seabass showed.that the nitrogen leaching was not significant. Besides, the decantation method was adequate since the faeces of turbot had good cohesion owing to the presence of alginate in the diets. Addition of alginate is known to improve faecal collection also in salmonids unless excess levels above 4% of alginate are used which might affect digestibility ŽStorebakken, 1985

Data obtained here indicate a starch digestibility of about 75%, the major dietary source being extruded peas, known to have similar digestibility of starch in the rainbow trout

ADC of starch from peas in the rainbow trout. Phosphorus availability is reported to vary with species, besides being influenced by different factors such as the chemical

Amino acid availability generally reflected protein digestibility. Currently, there is no data on amino acid requirements or availability in turbot. An approximation of IAA 1998 . Average AAAA decreased with increasing CGM levels in the diets. In European.

Seriola quinquera-

diata. fed a diet containing CGM, which they attributed to the acidity in the corn gluten meal. The decline in AAAA observed here, however is, far less than that observed by Paralichthys oliÕaceus., another

flatfish. They found values of below 50% for the ADC of protein as well as for AAAA ŽSalmo salar . fed a diet containing 45% of CGM showed AAAA values similar to those of this study when fish meal was partially replaced by CGM

demonstrated that turbot are capable to effectively utilise crystalline amino acids.Similar observations have already been made in rainbow trout fed a zein-based diet

Ictalurus punctatus.

Thebault et al., 1985 ..

Growth performances observed for turbots fed diet 1 and 2 were excellent. SGR

20% inclusion of CGM in partial replacement of fish meal has no adverse effects on led to similar conclusions. A total replacement of fish meal by CGM induced a growth reduction of nearly 30%. Beyond a decrease in the digestibility of diets rich in CGM, bad growth performances of turbot fed these diets were possibly due to the low biological value of such CGM-based diets, relatively rich in leucine and perhaps marginal in tryptophan in comparison with fish meal. This also possibly caused a reduction of feed intake in spite of the presence of inosine known to be a gustatory

Amino acid imbalances have also been found to be involved in reducing feed intake in

Feed efficiency was high in turbot fed diets 1 and 2. The values observed here with the best growth performances were higher than those recorded with rainbow trout Fauconneau, 1988; Morales et al., 1994 or seabass Ballestrazi et al., 1994 fed CGM. et al., 1993 . Both FE and PER were also related to protein ADC. Gomes et al. 1995 observed that when diet formulations were based on digestible protein contents, PER

varied little in rainbow trout, even with diets containing 100% of plant proteins CGMŽ and soybean, principally . In our study, digestible protein DP content decreased with.increasing CGM levels although diets were formulated to have similar DP levels, based on theoretical values for protein digestibility of CGM in salmonids.Total protein content of whole body of turbot was not influenced by dietary

on whole boby protein content. On the other hand, whole body fat content of turbot varied. Although turbot fed diets 1 and 2 had similar growth performances, those fed diet 2 had a total fat content higher than those fed diet 1. Nevertheless, contrary to many species, whole body fat content of turbot was low -3.5% ..A protein retention value above 40% for diet rich in fish meal has already been found

1991 or seabass Ballestrazi et al., 1994 under similar dietary conditions replacement.of fish meal by CGM . Protein and energy retention decreased with incorporation of.CGM in the diets. Arginine and lysine supplementation in diet 5 did not improve protein retention in spite of greater availability of these two amino acids. Similarly in carp,methionine, lysine and threonine supplementation to diets containing CGM and soybean earlier, a marginal deficiency in tryptophan, besides possible branched chain amino acid cannot be ruled out. This is probably also reflected in the decline in IAA retention and We observed that a dietary supplementation with arginine and lysine induced an increase of the concentrations of these two amino acids in the muscle as well as in the plasma. The results from tissue free amino acid levels and amino acid availability confirm that supplementation of EAA could improve the amino acid supply and balance

1995 showed an increase of plasma concentrations of lysine and methionine when the. diets were supplemented in these IAA. The relationship between essential amino acid 1979; Ogata, 1986 . Muscle is also an important reservoir of FAA. The concentrations. al., 1978; Kaushik and Luquet, 1979; Ogata, 1986 . Unfortunately, we could not obtain. reliable data on these two amino acids in the muscle of turbot with the analytical method used.

The concentration of free leucine increased in both muscle and plasma of turbot fed CGM based diets, accompanied by a reduction in the levels of isoleucine and of valine, led to an increase in plasma levels of isoleucine and valine. In lake trout, a dietary excess of leucine or isoleucine has been shown to cause an increase in the requiremen

grkg diet does not seem to affect the growth of rainbow trout Choo et al., 1991 ;although they observed a significant growth depression in trout fed a diet with much kg diet , the concentrations of other branched amino acids.

lestrazi et al., 1994 or rainbow trout Fauconneau, 1988; Olivia-Teles et al., 1994 . The

Cacerez-Martinez, 1984 and is much lower than values of 2–3% or above found in

Shimeno et al., 1993 . In the latter study, there was no difference between HSI of fish.fed a diet containing fish meal or plant proteins, whereas the HSI in turbot fed CGM based diets were low. This is probably due to a reduction of growth than to any specific effect of CGM, as also evidenced by mobilisation of body fat in turbot fed CGM-based

mixture of wheat gluten and crystalline amino acids without negative influences on growth of rainbow trout. In studies on the replacement of fishmeal, use of a combination 1997 . Inclusion of high levels of some plant protein sources can exacerbate problems. not only related to the essential amino acid balance but also with regard to the possible ANF are not as fully described in fish as in other terrestrial animals and much less so in marine teleosts.

The possible secondary physiological effects of dietary plant protein intake have also been little studied in fish. The decline in plasma triglyceride concentrations with 1993 . The decrease in whole body fat content along with the decrease in plasma. triglyceride concentrations also suggest significant lipid mobilisation in these groups exhibiting very poor growth rates. Plant proteins are known to affect both cholesterol

hypocholesterolemic effect of dietary soybean in rainbow trout. Plasma cholesterol 1995 , and also decreased with high dietary CGM levels..According to some authors, thyroid hormones and their activities are good biological

of thyroid regulation consists of peripheral conversion of T3 into T4 through a deiodinase. In our study, a good correlation between plasma T3 concentrations and

of both T3 and T4 concentrations in rainbow trout as well as turbot fed diets containing 30% of rapeseed meal, mainly attributed to high levels of glucosinolates, although there was no growth retardation. In this study, no such specific effect of corn gluten meal on thyroid concentrations was observed. The mechanisms involved and the possible conse-quences require further attention.