Volume 16, Issue 2 pp. 205-212
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Effects of dietary protein to energy ratios on growth and body composition of juvenile Chinese sucker, Myxocyprinus asiaticus

Y.C. YUAN

Y.C. YUAN

Key Lab of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, College of Fishery, Huazhong Agricultural University, Wuhan 430070, China

Nutrition Laboratory, College of Fishery, Huazhong Agricultural University, Wuhan 430070, China

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S.Y. GONG

S.Y. GONG

Key Lab of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, College of Fishery, Huazhong Agricultural University, Wuhan 430070, China

Nutrition Laboratory, College of Fishery, Huazhong Agricultural University, Wuhan 430070, China

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Z. LUO

Z. LUO

Key Lab of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, College of Fishery, Huazhong Agricultural University, Wuhan 430070, China

Nutrition Laboratory, College of Fishery, Huazhong Agricultural University, Wuhan 430070, China

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H.J. YANG

H.J. YANG

Nutrition Laboratory, College of Fishery, Huazhong Agricultural University, Wuhan 430070, China

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G.B. ZHANG

G.B. ZHANG

Nutrition Laboratory, College of Fishery, Huazhong Agricultural University, Wuhan 430070, China

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Z.J. CHU

Z.J. CHU

Nutrition Laboratory, College of Fishery, Huazhong Agricultural University, Wuhan 430070, China

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First published: 17 March 2010
Citations: 26
Correspondence: Prof. Shi Yuan Gong, College of Fisheries, Huazhong Agricultural University, Wuhan 430070, China. E-mail: [email protected]

(Correction added on 1 June 2009, after first online publication: The header ‘REVIEW’ was removed from the first page of this article.)

Abstract

A growth experiment was conducted to investigate effect of dietary protein to energy ratios on growth and body composition of juvenile Myxocyprinus asiaticus (initial mean weight: 10.04 ± 0.53 g, mean ± SD). Nine practical diets were formulated to contain three protein levels (340, 390 and 440 g kg−1), each with three lipid levels (60, 100 and 140 g kg−1), in order to produce a range of P/E ratios (from 22.4 to 32.8 mg protein kJ−1). Each diet was randomly assigned to triplicate groups of 20 fish in 400-L indoors flow-through circular fibre glass tanks provided with sand-filtered aerated freshwater. The results showed that the growth was significantly affected by dietary P/E ratio (P < 0.05). Fish fed the diets with 440 g kg−1 protein (100 and 140 g kg−1 lipid, P/E ratio of 31.43 and 29.22 mg protein kJ−1) had the highest specific growth rates (SGR) (2.16 and 2.27% day−1, respectively). However, fish fed the diet with 390 g kg−1 protein and 140 g kg−1 lipid showed comparable growth (2.01% day−1), and had higher protein efficiency ratio (PER), protein productive value (PPV) and energy retention (ER) than other groups (P < 0.05). No significant differences in survival were found among dietary treatments. Carcass lipid content was positively correlated with dietary lipid level, but irrespective of protein level and inversely correlated with carcass moisture content. Carcass protein contents increased with increasing dietary lipid at each protein level. The white muscle and liver composition showed that lipid increased with increasing dietary lipid level (P < 0.05). Dietary protein concentrations had significant effect on condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) (P < 0.05). However, dietary lipid concentrations had no significant effect on CF, HSI (P > 0.05). Based on these observations, 440 g kg−1 protein with lipid from 100 to 140 g kg−1 (P/E ratio of 29.22 to 31.43 mg protein kJ−1) seemed to meet minimum requirement for optimal growth and feed utilization, and lipid could cause protein-sparing effect in diets for juvenile Chinese sucker.

Introduction

Protein, the most expensive component in fish feeds, plays an important role in growth of fish. The utilization of dietary protein is related to both protein level and availability of non-protein energy sources. Excessive dietary protein will be used for energy, resulting in higher specific dynamic action and more excreted ammonia nitrogen (LeGrow & Beamish 1986). Inclusion of non-protein energy sources has been shown to lower dietary protein used for energy and increase protein utilization for growth, a process known as ‘protein sparing’ (El-Sayed & Teshima 1992; Morais et al. 2001). However, the use of non-protein energy in fish diets must be closely evaluated because excessive non-protein energy has a few disadvantages: (i) reduces feed intake (Lovell 1979); (ii) produces fatty fish (Reinitz et al. 1978; Fu et al. 2001); (iii) inhibits the utilization of other nutrients (Winfree & Stickney 1981). Therefore, an optimal dietary protein to energy ratio (P/E) should be taken into account when the fish diet is formulated. A number of studies have been conducted to determine the optimal P/E ratio for some cultured fishes (Webster et al. 1995; Tibaldi et al. 1996). However, the optimal value may vary by fish species, fish size, variation in diet formulation and culture system.

Chinese sucker, Myxocyprinus asiaticus, is an endemic freshwater fish in China and the only representive of family Catostomidae in Asia. The fish is naturally distributed mainly in the Yangtze River, especially in the upper reaches. The wild fish resources were greatly damaged because of the environmental changes and over fishing and late in sexual mature, to date the Chinese sucker has been an endangered species and has been listed in the second class of preserved animals in China.

The Chinese sucker is a species of great potential value in aquaculture. In the absence of some specific feed for Chinese sucker, fish producers have customarily fed eel feed (480 g kg−1 protein), whereas Chinese sucker fed eel feed which is an easily produced fatty liver for long time. Chinese sucker is an omnivorous and partial to carnivorous species that has been widely cultured in China because of its delicious meat and rapid growth. Traditional culture of this fish mainly depends on chopped or minced trash fish and fish worm, which is difficult to store, easy to deteriorate water quality and may result in the spread of diseases. Recently, because of the shortage of fishery resources, available trash fish could not meet the demand for the expanding farming of Chinese sucker in China. Therefore, studies on its nutrition should be carried out to develop cost-effective and nutritionally balanced diets for this fish. To date, a few preliminary studies have been conducted on the nutrient requirements for this fish species (Chen et al. 2008), but no information was available on the optimal protein and lipid levels. Therefore, the present study was designed to determine the optimal P/E ratio to develop commercial feed for Chinese sucker.

Materials and methods

Experimental diets

Using white fish meal and soybean meal as protein sources, fish oil as the lipid source, wheat meal as the carbohydrate source, nine practical diets were formulated to contain three protein levels (340, 390 and 440 g kg−1), each with three lipid levels (60, 100 and 140 g kg−1), in order to produce a range of P/E ratios from 22.4 to 32.8 mg protein kJ−1 (Table 1). Because digestible energy values for the ingredients had not been determined for Chinese sucker, available energy was calculated using physiological fuel values of 4, 9 and 4 kcal g−1 for protein, lipid and carbohydrate, respectively (Garling & Wilson 1976). The dry ingredients (ground to pass 120 μm sieve) were thoroughly mixed in a food mixer, then all the ingredients were thoroughly mixed with fish oil, and distilled water was added to (400 g kg−1, v/w) obtain a stiff dough. The moist diet was then extruded through a pelletizer with a 2.0-mm-diameter pellet. The resultant pellets were dried in an oven at 45 °C until the moisture was reduced to <100 g kg−1. The dry pellets were placed in covered plastic bags and stored in a freezer at –20 °C until being fed.

Table 1. Formulation and proximate composition of the experimental diets
Ingredient (g kg−1) Diet no. (protein/lipid)
Diet1 (34/6) Diet2 (34/10) Diet3 (34/14) Diet4 (39/6) Diet5 (39/10) Diet6 (39/14) Diet7 (44/6) Diet8 (44/10) Diet9 (44/14)
White fish meal1 320 320 320 400 400 400 480 480 480
Soybean meal2 260 260 260 260 260 260 260 260 260
Fish oil3 50 90 130 50 90 130 50 90 130
a-starch 50 50 50 50 50 50 50 50 50
Wheat meal 240 200 160 160 120 80 80 40 0
Rice meal 35 35 35 35 35 35 35 35 35
Vitamin premix4 5 5 5 5 5 5 5 5 5
Mineral premix5 20 20 20 20 20 20 20 20 20
Binder6 20 20 20 20 20 20 20 20 20
Nutrition composition
Crude protein 345 346 349 394 396 398 445 447 449
Available energy (kJ g−1) 12.81 13.84 14.87 12.91 13.95 14.96 13.01 14.05 15.09
P/E mg protein (kJ−1) 27.10 24.98 22.48 30.74 28.29 26.20 32.86 31.43 29.22
Crude lipid 66 106 146 63 100 139 65 104 144
Ash 126 123 120 127 125 118 137 125 121
  • 1 Gao Long Diary Company, WuHan, China, Imported from USA.
  • 2 Soybean meal, crude protein 46.4% dry matter, crude lipid 1.9% dry matter; obtained from Gao Long Diary Company, WuHan, China.
  • 3 Gao Long Diary Company, WuHan, China.
  • 4 Vitamin premix (mg/kg diet) thiamin 50 mg; riboflavin, 90 mg; pyridoxine HCl, 40 mg; vitamin B12, 0.2 mg; vitamin K3, 20 mg; inositol, 1600 mg; pantothenic acid, 120 mg; niacin acid, 400 mg; folic acid, 40 mg; biotin, 2.40 mg; retinol acetate, 64 mg; cholecalciferol, 10 mg; alpha-tocopherol, 240 mg; ascorbic acid, 4000 mg; choline chloride, 5000 mg; ethoxyquin 300 mg, wheat middling, 36.78 g.
  • 5 Mineral premix (mg or g kg−1 diet): NaF, 2 mg; KI, 0.8 mg; CoCl2-6H2O (1%), 50 mg; CuSO4-5H2O, 10 mg; FeSO4-H2O, 80 mg; ZnSO4-H2O, 50 mg; MnSO4-H2O,60 mg; MgSO4-7H2O, 1200 mg; Ca(H2PO3)2-H2O, 3000 mg; NaCl, 100 mg; Zoelite, 15.45 g.
  • 6 Binder :1.5%α-starch and 0.5%HJ-II.

Experimental procedures

Experimental fish were obtained from a commercial farm. Prior to the start of the experiment, Chinese sucker (M. asiaticus) juveniles were reared in 1600-L indoors flow-through circular fibreglass tanks provided with sand-filtered aerated freshwater for 2 weeks to acclimate to the experimental conditions. Fish were fed twice daily with a commercial diet to satiation during this period. The feeding trial was conducted in 400-L indoors flow-through circular fibreglass tanks provided with sand-filtered aerated freshwater. At the start of the experiment, the fish were starved for 24 h and weighed after being anesthetized with eugenol (1 : 10 000) (Shanghai Reagent Co., Shanghai, China). Fish of similar sizes (10.04 ± 0.53 g, mean ± SD) were randomly distributed into 27 400-L indoors flow-through circular fibre glass tanks, and each tank was stocked with 20 juveniles. Each diet was assigned to triplicate tanks. Fish were hand-fed to apparent satiation twice (09 : 00 and 16 : 00) daily. The feeding trial lasted for 8 weeks. Fish were weighed every 2 weeks to monitor growth. The amount of feed consumed by the fish in each tank was recorded daily. Fecal matter was removed before each morning feeding. Tanks were thoroughly cleaned every 2 weeks when the fish were removed for weighing. Mortality was checked daily.

During the experimental period, 12-h light: 12-h dark photoperiod was maintained; the temperature ranged from 22 to 25 °C, whereas it was above 25 °C for only a few days; dissolved oxygen content was approximately 6 mg l−1; pH 7.6–8.3.

Analysis and measurement

At the termination of the experiment, the fish were starved for 24-h before harvest. Total number and mean body weight of the fish in each tank were measured. A sample of 40 fish at the initiation of feeding experiment and 10 fish per tank at the termination were collected and stored frozen (–20 °C) for determination of proximate carcass composition. Another seven fish from each aquarium were randomly selected, dissected to obtain liver and white muscle samples, and viscerosomatic index (VSI), hepatosomatic index (HSI) were calculated. Liver and muscle samples were also kept at –20 °C prior to being analyzed. Proximate composition analysis on feed ingredients, experimental diets and fish body were performed by the standard methods of AOAC (1995). Samples of diets and fish were dried to a constant weight at 105 °C to determine moisture. Protein was determined by measuring nitrogen (N × 6.25) using the Kjeldahl system method after an acid digestion using an auto Kjeldahl System (2300 Auto analyzer, Foss Tecator, AB, Hoganas, Sweden); lipid by ether extraction using Soxhlet; ash by combustion at 550 °C, and body energy by an adiabatic bomb calorimeter (PARR1281, Automatic Energy Analyser, Moline, IL, USA).

Statistical analysis

The results were presented as means ± SD of three replicates. Data from each treatment were subjected to one-way analysis of variance (anova), two-way anova and correlation analysis where appropriate. When overall differences were significant (P < 0.05), Tukey’s multiple range test was used to compare the mean values between individual treatment. Statistical analysis was performed using the spss 16.0 for Windows (SPSS, Michigan Avenue, Chicago, IL, USA).

Results

Effect of dietary protein to lipid ratios on growth performance and feed utilization was shown in Table 2. The juvenile Chinese sucker showed good growth performance during the 8-week feeding trial, increasing from an initial average weight 10.04 g to 25.13–35.98 g. The survival ranged from 90% to 100% and averaged 96.5% (Table 2), and there was no effect of dietary treatment on mortality. Dietary P/E ratios significantly affected weight gain (WG) and specific growth rate (SGR) (P < 0.05). SGR showed increasing trend with increasing dietary protein content from 340 to 440 g kg−1, and feed conversion ratio (FCR) decreased with increasing dietary protein (P < 0.05), but was not markedly affected by lipid level (P > 0.05) (Table 2). Fish fed Diet 8 (440/100) and Diet 9 (440/140) had the highest and similar SGR, closely followed by those fed Diet 6 (390/140) and Diet 7 (440/60). However, fish fed the diets with the dietary lipid level at the lowest dietary protein (340 g kg−1) and Diet 4 (390/60) showed significantly lower growth compared with the other protein levels (P < 0.05). The poorest growth was observed in the fish fed diet containing 340 g kg−1 protein and 60 g kg−1 lipid (Table 2). Dietary protein content significantly affected feed intake (FI) (P < 0.05). Protein efficiency ratio (PER), protein productive value (PPV), energy retention (ER) generally increased with increasing dietary lipid level at each dietary protein level. and, the highest values were always recorded in fish fed Diet 9 with 440 g kg−1 dietary protein and 140 g kg−1 lipid.

Table 2. Growth performance and feed utilization efficiency of Myxocyprinus asiaticus fed diets with varying P/E ratio for 56 days
Dite no. (Protein/Lipid) IBW (g) FBW (g) WG (%) SGR (% day−1) FI g 100 g−1 B.W. day−1 FCR PER ER (%) PPV (%) Survival (%)
Diets 1 (34/6) 10.32 ± 0.18 25.13 ± 1.09e 144 ± 9.46e 1.59 ± 0.07d 3.58 ± 0.08a 2.40 ± 0.14a 1.21 ± 0.07e 20.58 ± 1.29f 17.32 ± 2.16d 0.98 ± 0.03b
Diets 2 (34/10) 9.93 ± 0.06 25.91 ± 0.92de 161 ± 10.45de 1.71 ± 0.08c 3.51 ± 0.07a 2.21 ± 0.12a 1.31 ± 0.07de 22.23 ± 0.89ef 17.32 ± 1.58cd 1.00 ± 0.00a
Diets 3 (34/14) 10.24 ± 0.17 27.97 ± 0.57cd 173 ± 10.23d 1.79 ± 0.07c 3.17 ± 0.03b 1.92 ± 0.08b 1.49 ± 0.08bc 25.55 ± 1.47cde 22.33 ± 2.54bc 0.92 ± 0.03c
Diets 4 (39/6) 10.24 ± 0.10 27.36 ± 0.85cde 168 ± 10.70de 1.76 ± 0.11c 3.21 ± 0.06b 1.97 ± 0.10b 1.29 ± 0.09d 24.97 ± 2.10de 17.99 ± 1.41d 0.98 ± 0.03ab
Diets 5 (39/10) 10.22 ± 0.20 28.44 ± 0.95c 173 ± 10.00d 1.79 ± 0.09c 3.05 ± 0.08b 1.85 ± 0.10b 1.37 ± 0.08cde 26.16 ± 0.39cd 20.93 ± 0.88bcd 0.93 ± 0.03abc
Diets 6 (39/14) 10.44 ± 0.17 31.63 ± 0.77b 209 ± 8.15c 2.01 ± 0.10b 2.77 ± 0.05c 1.52 ± 0.05c 1.66 ± 0.09ab 30.81 ± 0.97ab 26.35 ± 1.09a 0.90 ± 0.05c
Diets 7 (44/6) 10.23 ± 0.35 31.85 ± 0.71b 216 ± 13.72c 2.05 ± 0.09b 2.85 ± 0.03c 1.54 ± 0.07c 1.47 ± 0.09bcd 28.50 ± 1.19bc 20.98 ± 0.67bcd 1.00 ± 0.00a
Diets 8 (44/10) 10.06 ± 0.16 33.76 ± 0.81ab 236 ± 11.21b 2.16 ± 0.07ab 2.70 ± 0.05c 1.40 ± 0.06cd 1.61 ± 0.06b 31.79 ± 0.96ab 24.98 ± 1.33ab 0.97 ± 0.03abc
Diets 9 (44/14) 10.08 ± 0.14 35.98 ± 0.70a 257 ± 2.70ab 2.27 ± 0.08a 2.50 ± 0.04d 1.24 ± 0.02d 1.80 ± 0.10a 33.00 ± 0.90a 27.20 ± 2.01a 0.97 ± 0.03abc
anova (P-value)
Protein 0.000 0.001 0.000 0.000 0.000 0.002 0.000 0.006 0.133
Lipid 0.078 0.085 0.102 0.048 0.062 0.000 0.029 0.000 0.004
Lipid×protein 0.456 0.427 0.418 0.418 0.315 0.562 0.220 0.099 0.114
P/E 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.003
  • B.W., body weight.
  • Values are mean ± SD of three groups per treatment. Values within the same column with different letters are significantly different (P < 0.05).
  • IBW (g/fish), initial mean body weight.
  • FBW (g/fish), final mean body weight.
  • WG (%), 100*[(final mean wt − initial mean wt)/initial wt];
  • SGR (% day−1), specific growth rate = 100*[(in final weight − in initial weight)/days of experiment].
  • FCR, feed conversion ratio = dry feed intake/wet weight gain.
  • PER, protein efficiency ratio = wet weight gain/dry protein intake.
  • FI, feed intake (FI) = feed consumption (g)/((Wt + W0)/2) × t); ER, energy retention = (Wt × E1− W0×  E2)/(Id ×E), where Wt is final body weight, W0 is initial body weight, t is experimental duration in day, Id is feed intake of dry matter. E, E1 and E2 represent energy content in diet, final fish body and initial fish body, respectively.
  • PPV, protein productive value = [(final body N − initial body N)/N intake].

The proximate composition of whole body of juvenile Chinese sucker fed the diets containing various dietary protein to lipid ratios was shown in Table 3. Moisture content was not significantly affected by dietary protein level, lipid level and P/E ratio (P > 0.05). Whole body protein tended to increase with dietary lipid level at the same protein level (P < 0.05), and was highest for fish fed the 440 g kg−1 protein diet with P/E ratio of 29.22 mg protein kJ−1 (P < 0.05). The interaction between dietary lipid and protein level had no significant difference on body protein (P > 0.05). Whole body lipid increased with increasing dietary lipid level (P < 0.05). Dietary P/E ratio affected carcass ash content with the inverse trend as carcass protein content.

Table 3. The effect of diets with varying P/E ratio on composition of whole body in Myxocyprinus asiaticus (g kg−1 on a wet weight basis)
Diets no. Moisture Crude protein Crude lipid Crude ash Energy (kJ g−1 w.w.)
Initial 778 ± 11.4 154 ± 5.9 69 ± 5.0 33 ± 0.9 52 ± 1.8
Diets 1 (34/6) 755 ± 9.6ab 148 ± 5.6b 70 ± 2.8e 35 ± 2.0a 55 ± 2.1c
Diets 2 (34/10) 761 ± 3.5ab 148 ± 5.7b 72 ± 1.3e 31 ± 1.5bcd 56 ± 1.6c
Diets 3 (34/14) 756 ± 9.3ab 153 ± 9.5b 98 ± 3.0ab 31 ± 1.7bcd 65 ± 1.1a
Diets 4 (39/6) 756 ± 13.8ab 144 ± 6.1b 84 ± 5.1d 31 ± 1.5bcd 59 ± 3.0bc
Diets 5 (39/10) 752 ± 4.6b 155 ± 3.5ab 86 ± 3.0cd 32 ± 1.5bcd 62 ± 1.6ab
Diets 6 (39/14) 753 ± 9.4b 158 ± 6.3ab 94 ± 3.2bc 29 ± 1.7cd 64 ± 0.6a
Diets 7 (44/6) 760 ± 6.9b 148 ± 3.4b 72 ± 0.8e 32 ± 1.5abc 55 ± 0.9c
Diets 8 (44/10) 753 ± 2.0ab 154 ± 1.4ab 82 ± 2.2d 29 ± 0.9d 59 ± 1.1bc
Diets 9 (44/14) 740 ± 6.9b 170 ± 5.1a 78 ± 3.3de 26 ± 0.7e 61 ± 1.9ab
anova (P-value)
Protein 0.315 0.144 0.062 0.012 0.116
Lipid 0.239 0.002 0.002 0.005 0.000
Lipid × protein 0.205 0.106 0.000 0.008 0.013
P/E 0.189 0.001 0.000 0.000 0.000
  • w.w., wet weight.
  • Values are mean ± SD of three groups per treatment. Values within the same column with different letters are significantly different (P < 0.05).

In general, the white muscle composition was markedly influenced by dietary protein level and dietary P/E ratio (P < 0.05) (Table 4). White muscle protein increased with increasing dietary protein, and decreasing dietary P/E ratio at each protein level. The interaction between dietary lipid and protein level had significant effect on white muscle protein content (P < 0.05). Dietary treatments did not significantly affect muscle moisture (P > 0.05). At the same protein level, lipid content of white muscle also increased with dietary lipid levels (P < 0.05). The lipid content of liver significantly increased with dietary lipid level (P < 0.05) (Table 4). In contrast, liver moisture content was highest for fish which fed the 340 g kg−1 protein diet with 60 g kg−1 lipid and P/E ratio of 27.10 mg protein kJ−1, and significantly decreased with the increasing dietary protein level (P < 0.05). Dietary protein concentrations had significant effect on condition factor (CF), HSI and VSI (P < 0.05). Chinese sucker fed Diet 1 (340/60) in the present experiment had lowest CF, VSI and HSI (Table 5). However, dietary lipid concentrations had no significant effect on CF, VSI and HSI.

Table 4. The effect of diets with varying P/E ratio on composition of white muscle and liver in Myxocyprinus asiaticus (g kg−1 on a wet weight basis)
Diets no Muscle Liver
Moisture Crude protein Crude lipid Moisture Crude lipid
Initial 782 ± 4.3 167 ± 3.3 22 ± 2.4 731 ± 1.3 131 ± 1.2
Diets 1 (34/6) 793 ± 3.9a 158 ± 4.4bcd 19.7 ± 1.2b 731 ± 7.7a 156 ± 3.8e
Diets 2 (34/10) 787 ± 2.4ab 161 ± 5.1abcd 23.3 ± 3.3ab 726 ± 1.9ab 173 ± 2.5cde
Diets 3 (34/14) 791 ± 7.3ab 154 ± 2.0d 24.9 ± 4.7ab 715 ± 5.0bc 178 ± 4.5bcd
Diets 4 (39/6) 787 ± 5.8ab 158 ± 4.8bcd 20.1 ± 0.9b 711 ± 8.2c 166 ± 6.9e
Diets 5 (39/10) 785 ± 3.7ab 155 ± 4.7cd 24.2 ± 3.06b 712 ± 1.5c 169 ± 2.2de
Diets 6 (39/14) 782 ± 2.6b 159 ± 2.2bcd 28.5 ± 3.6a 717 ± 6.0bc 184 ± 3.3ab
Diets 7 (44/6) 789 ± 2.7ab 156 ± 1.9cd 21.8 ± 2.1ab 720 ± 2.2abc 174 ± 1.7bcd
Diets 8 (44/10) 784 ± 6.5ab 170 ± 4.8ab 27.4 ± 2.0ab 721 ± 1.0abc 181 ± 2.4abc
Diets 9 (44/14) 787 ± 5.5ab 171 ± 5.5a 27.0 ± 2.4ab 714 ± 2.1bc 186 ± 2.5a
anova (P-value)
Protein 0.055 0.008 0.329 0.007 0.050
Lipid 0.265 0.345 0.000 0.284 0.001
Lipid × protein 0.699 0.003 0.642 0.009 0.246
P/E 0.239 0.000 0.011 0.001 0.000
  • Values are mean ± SD. of three groups per treatment. Values within the same column with different letters are significantly different (P < 0.05).
Table 5. The Effect of diets with varying P/E ratio on CF, HSI and VSI in Myxocyprinus asiaticus reared in indoors flow-through circular fibre glass tanks
Diet no. (protein/lipid) CF HSI VSI
Diets 1 (34/6) 2.38 ± 0.06f 0.75 ± 0.08e 7.68 ± 0.08c
Diets 2 (34/10) 2.42 ± 0.01ef 0.80 ± 0.07de 7.81 ± 0.12bc
Diets 3 (34/14) 2.54 ± 0.06de 0.82 ± 0.03cd 7.96 ± 0.25abc
Diets 4 (39/6) 2.49 ± 0.01de 0.86 ± 0.06bcd 7.93 ± 0.33abc
Diets 5 (39/10) 2.53 ± 0.07de 0.89 ± 0.09b 8.09 ± 0.12abc
Diets 6 (39/14) 2.62 ± 0.09cd 0.86 ± 0.05bc 8.31 ± 0.15ab
Diets 7 (44/6) 2.59 ± 0.05cd 0.89 ± 0.03b 8.10 ± 0.15abc
Diets 8 (44/10) 2.77 ± 0.04ab 1.05 ± 0.05a 8.13 ± 0.13abc
Diets 9 (44/14) 2.79 ± 0.06a 1.04 ± 0.04a 8.42 ± 0.16a
anova (P-value)
Protein 0.000 0.000 0.002
Lipid 0.050 0.145 0.025
Lipid × protein 0.188 0.000 0.934
P/E 0.000 0.000 0.002
  • Values are mean ± SD of three groups per treatment. Values within the same column with different letters are significantly different (P < 0.05).
  • CF = 100*(live weight, g)/(body length, cm)3.
  • HSI = 100*(liver wt/body wt).
  • VSI = 100*(viscera wt/body wt).

Discussion

In the present study, the growth performance of Chinese sucker was significantly affected by dietary P/E ratio. The growth response in terms of SGR observed in this study ranged between 1.59 and 2.27% day−1 were better than those reported for this species in previous study (between 1.08 and 1.54, Chen et al. 2008). Chinese sucker grew best when fed the two diets containing 100 and 140 g kg−1 lipid at 440 g kg−1 protein (P/E ratios of 31.43 mg protein kJ−1 and 29.22 mg protein kJ−1). However, regarding the costs of the diet, the growth, maximun protein retention and minimal pollution, 31.43 mg protein kJ−1 is more appropriate than 29.22 mg protein kJ−1 because of a build-up of energy in the fish body which is not desirable if the energy retained is in the form of lipid, maybe produce fatty fish, which agrees with (Fu et al. 2001), particularly liver lipid which is of no commercial value because it will ultimately be discarded with the liver during processing (Tibbetts et al. 2005). However, fish fed the diet with 390 g kg−1 protein and 140 g kg−1 lipid had similar SGR, PER and ER as those fed the above two diets, the growth rates of juvenile Chinese sucker fed diets with 340 g kg−1 protein level were lower compared with 440 g kg−1 protein levels, indicated that 340 g kg−1 protein could not meet the minimum requirement. This was similar to some other studies (Webster et al. 1995; Ai et al. 2004; Luo et al. 2004). The suitable dietary protein requirement obtained from the present study is 440 g kg−1(the protein digestibility of the white fish meal and soybean meal were 91.18 and 83.2% in the experimental diet; Yuan et al., unpublished data), which is close to the requirement of European sea bass (45%, Perez et al. 1997), and Asian sea bass, Lates calcarifer (42.5%, Catacutan & Coloso 1995), but higher than the optimal dietary protein requirement for juvenile Chinese sucker has been reported to 40% and 39.73% (using casein as protein sources) (Chen et al. 2008). The slight differences among these experiments may be the result of different diet formulations, different fish sizes, and differences between species or different methodology applied. At all dietary protein levels, the growth rates of juvenile Chinese sucker fed diets with 60 g kg−1 lipid level were lower compared with higher lipid levels. The poor growth was likely because of the lower energy at 60 g kg−1 lipid. Increasing dietary lipid level improved SGR, PER, ER, PPV, suggesting an obvious protein sparing effect of lipid. This effect has previously been observed in other fish species (Morais et al. 2001; Mathis et al. 2003). The FCR values (1.24–2.40) obtained in this study were lower than those in the study using pelleted diets (1.43–2.03, Chen et al. 2008). FCR decreased with the increase of dietary lipid level. To ensure dietary feed intake of whole fish stock high daily feed ratios of 5–6% total fish biomass per day were favorable for fish to concentrate and feed (juvenile Chinese sucker tended to concentrate and feed), which resulted in excessive amounts of uneaten feed and probably to high FCR calculated by the feed supply. Territorial behavior of dominant individuals, which were able to defend feeding point and feed resources, seem to influence FCR negatively. This negative impact on FCR by aggressive feeding behavior of dominant individuals was also described for Eurasian perch (Melard et al. 1996; Schulz et al. 2008).

In the present study, the optimal P/E ratio (29.22 mg protein kJ−1) is within the range reported for some other fish species. The optimal P/E ratio has been reported to be 23.7–26.6 mg protein kJ−1 for sunshine bass (Keembiyehetty & Wilson 1998), 21.1–35.2 mg protein kJ−1 for channel catfish (Garling & Wilson 1976; Reis et al. 1989), 30.62 mg protein kJ−1 for Asian seabass (Catacutan & Coloso 1995), and 27.5–29.5 mg protein kJ−1 for mutton snapper (Watanabe et al. 2001). In contrast, Luo et al. (2005) reported a suitable P/E ratio of 35.41–39.95 mg protein kJ−1 for grouper. To a certain extent, optimal P/E ratio varies by fish species, and ever for the same species in different studies. These variations may be due to the following two aspects besides fish species. One is experimental dietary P/E level. The different design of dietary nutrient level affects the estimation of nutrient requirement (Mercer 1982). Therefore, the estimation for optimal dietary P/E ratio also varies by its design level. In the study with sunshine bass, Webster et al. (1995) used four protein levels and two lipid levels to produce eight different dietary P/E ratios (from 15.4 to 28.9 mg protein kJ−1). Their results showed that sunshine bass required a diet containing 410 g kg−1 protein, or a P/E ratio >23.7 mg protein kJ−1, whereas higher P/E ratios (from 21.7 to 40.1 mg protein kJ−1) were used in the study of (Keembiyehetty & Wilson 1998), who reported an optimal E/P ratio of 9 kcal g−1 protein (26.6 mg protein kJ−1). The other is the difference in dietary ingredients. To achieve the better growth, the dietary ingredients should be readily digestible and provide sufficient essential amino acids. However, different ingredients differ in their amino acid composition and availability NRC (1993). Therefore, the optimal dietary P/E ratio varied for the same physiological fuel values (Webster et al. 1995; Tibaldi et al. 1996), which probably affects the accuracy of optimal dietary P/E ratio. Consequently, the digestible energy values for the ingredients should be determined in further study with Chinese sucker. Nevertheless, the experimental formulation used in this study was based on commercially available feed ingredients. Hence, this result is probably applicable to commercial feed production.

In this study, the data on carcass, white muscle and liver composition showed that lipid content of carcass, white muscle and liver increased with increasing dietary lipid, similar to the previous studies (Keembiyehetty & Wilson 1998; Luo et al. 2005). Carcass moisture was inversely related to carcass lipid as seen in other fish (Zeitler et al. 1984; Parazo 1990; Luo et al. 2005). Body protein content increased with increasing lipid level at the same protein level, which agrees with Ai et al. (2004).

In this study, CF achieved the maximum value at the diet containing 440 g kg−1 protein and 140 g kg−1 lipid with P/E of 29.22 mg protein kJ−1. VSI was influenced by dietary protein level, lipid level and dietary P/E ratio. Dietary lipid concentrations had no significant effect on HSI. Dietary protein concentrations had no significant effect on HSI. Chinese sucker fed diet containing 340 g kg−1 protein and 60 g kg−1 lipid with P/E of 27.10 mg protein kJ−1 in the present experiment had lowest CF, VSI and HSI, which was in agreement with Jover et al. (1999) who reported that yellowtail fed 450 g kg−1 CP showed lower CF, VSI and HSI than fish fed 500 g kg−1 CP. In contrast, Kim et al. (2002) reported that HSI was inversely related to dietary protein level in juvenile haddock. Lee et al. (2002) reported that CF was not affected by either dietary protein or lipid level and that HSI and VSI of fish fed the 140 g lipid kg−1 diet were higher than that of fish fed 70 g kg−1 lipid, but no signs indicated that HSI and VSI were affected by dietary protein level.

In conclusion, our results suggest that the diet containing 440 g kg−1 protein with lipid from 100 to 140 g kg−1 (P/E ratio of 29.22 to 31.43 mg protein kJ−1) seemed to meet minimum requirement for optimal growth and feed utilization, and lipid could cause protein-sparing effect in diets for juvenile Chinese sucker.

Acknowledgements

The study was supported by the Province Key Technologies Program for Great industrialization project in Wuhan. We thank G.B. Zhang for his help in diet production. Thanks are also due to Y.J. Wang, Y.H. Zhao & H.J. Yang for their assistance in the study.

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