Chinese Journal of Oceanology and Limnology http://dx.doi.org/10.1007/s00343-015-3349-x

Growth and energy budget of juvenile lenok in relation to ration level*

LIU Yang (刘洋) 1 , 2 , 3 , LI Zhongjie (李钟杰) 1 , ZHANG Tanglin (张堂林)1 , YUAN Jing (苑晶)1 , MOU Zhenbo (牟振波) 3 , LIU Jiashou (刘家寿) 1, ** 1 State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072 , 2 University of Chinese Academy of Sciences, Beijing 100049, China 3 Heilongjiang River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Harbin 150070 , China

Received Feb. 20, 2014; accepted in principle Apr. 14, 2014; accepted for publication Jul. 16, 2014 © Chinese Society for Oceanology and Limnology, Science Press, and Springer-Verlag Berlin Heidelberg 2015

Abstract We evaluated the effect of ration level (RL) on the growth and energy budget of lenok Brachymystax lenok . Juvenile lenok (initial mean body weight 3.06±0.13 g) were fed for 21 d at fi ve different ration levels: starvation, 2%, 3%, 4% bwd (body weight per day, based on initial mean values), and apparent satiation. Feed consumption, apparent digestibility, and growth were directly measured. Specifi c growth rates in terms of wet weight, dry weight, protein, and energy increased logarithmically with an increase in ration levels. The relationship between specifi c growth rate in terms of wet weight (SGRw, %/d) and RL (%) was characterized by a decelerating curve: SGRw=-1.417+3.166ln(RL+1). The apparent digestibility coeffi cients of energy exhibited a decreasing pattern with increasing ration level, and there was a signifi cant difference among different RLs. Body composition was signifi cantly affected by ration size. The relationship between feed effi ciency rate in terms of energy (FERe) and RL was: FERe=-14.167+23.793RL–3.367(RL)2 , and the maximum FERe was observed at a 3.53% ration. The maintenance requirement for energy of juvenile lenok was 105.39 kJ BW (kg) -0.80/d, the utilization effi ciency of DE for growth was 0.496. The energy budget equation at satiation was: 100IE=29.03FE+5.78(ZE+UE)+39.56 HE+25.63 RE, where IE is feed energy, FE is fecal energy, ZE+UE is excretory energy, HE is heat production, and RE is recovered energy. Our results suggest that the most suitable feeding rate for juvenile lenok aquaculture for wet weight growth is 2.89% bwd, whereas for energy growth, the suggested rate is 3.53% bwd at this growth stage.

Keyword : ration level; growth; energy budget; Brachymystax lenok

1 INTRODUCTION Brachymystax lenok is a salmonid that is endemic to cold freshwater habitats in north-east Eurasia The consumption of salmonids is increasing in (Alekseyev et al., 2003). This species is one of the China where salmon production has increased from few salmonids found in China (Dong and Jiang, 14 235 t in 2004 to 21 562 t in 2011 (BMFA 2005, 2008). However, the abundance of the wild population 2012). In response to the increased demand for salmon, has decreased signifi cantly because of over-fi shing, exotic species such as Atlantic salmon Salmo salar , habitat degradation, and environmental pollution. As rainbow trout, Oncorhynchus mykiss , and masou a result, this commercially important species has now salmon, Oncorhynchus masou , have been introduced into China’s aquaculture industry during the past few decades (Sun and Wang, 2010). However, the * Supported by the Special Fund for Agro-Scientifi c Research in the introduction of non-native salmonids represents a risk Public Interest of China (No. 201003055), the National Key Technology to the persistence of native salmonid species and the Research and Development Program of China (Nos. 2012BAD25B10, 2012BAD26B05), and the Central-Level Non-Profi t Scientifi c Research health of aquatic ecosystems because of their potential Institutes Special Funds of China (No. HSY201412) negative impact on native species (Fausch, 2007). ** Corresponding author: [email protected] CHIN. J. OCEANOL. LIMNOL.,

Table 1 Formulation (as a percentage of dry weight) and Table 2 Performance of juvenile Brachymystax lenok at chemical composition of the experimental diet for different rations (mean±SD)

juvenile lenok Brachymystax lenok Ration level (% BW/d) Parameter Ingredients % dry weight Starvation 2 3 4 Satiation meal a 60.20 Initial BW (g/fi sh) 3.03 3.05 3.06 3.08 3.07 Wheat fl our 19.55 Final BW (g/fi sh) 2.29 4.22 4.9 5.64 7.37 Soybean meal 6.00 Feed intake (g/fi sh/d) 0 0.06 0.09 0.12 0.22 Fish oil 5.75 DE intake (kJ/fi sh/d) 0 0.83 1.24 1.66 2.99 Mineral premix c 5.00 DE intake (kJ kg - 0.80/d )* 0 134.48 211.97 233.87 371.32 Vitamin premix d 0.30 Weight gain (g/fi sh/d) -0.04 0.06 0.09 0.12 0.19 Soybean lecithin 1.00 Energy retention -0.34 0.19 0.33 0.54 0.92 (kJ/fi sh/d) Choline chloride 0.2 Energy retention Sodium alginate 1.00 -71.29 30.97 49.21 75.75 114.49 (kJ kg -0.80 /d)

Cr2 O 3 1.00 * kg -0.80 , metabolic BW, following the recommendation of Brett and Groves Dry matter 85.38 (1979). Percentage of dry matter Crude protein 46.58 The relationship between growth rate and RL in fi sh is very important for the commercial success of any Crude lipid 11.96 aquaculture venture because feed accounts for the Ash 14.48 majority of the total production costs (Khan and Gross energy (MJ/kg) 19.07 Abidi, 2010). However, it is also important to Digestible energy (MJ/kg) 13.53 determine feed conversion effi ciency, which is a the fi sh meal used in the diet was from Peru; b digestible energy (DE) essential for evaluating energy fl ow between trophic c measured after Cho et al. (1982); mineral premix (g/kg): Ca(PO4 H 2 ) 2 ·H 2 O levels in natural aquatic communities (Penczak et al., (30), CaCO3 (6.5), KCl (2.5), NaCl (4), MnSO 4 ·H 2 O (0.2), FeSO 4 ·7H 2 O 1984; Armstrong and Hawkins, 2008). (1.5), MgSO 4 (4.6), KI (0.02), CuSO 4 ·5H 2 O (0.05), ZnSO 4 ·7H 2 O (0.2), -2 -2 In an attempt to improve effi ciency in the farming CoSO 4 ·7H 2 O (0.05), Na 2 SeO 3 (0.218×10 ), Al2 (SO 4 ) 3 ·18H 2 O (1×10 ); d vitamin premix (mg/kg): vitamin premix and mineral element premix of lenok juveniles, researchers have evaluated several provide (mg/kg or IU/kg diet): VA 8000 IU, VE 70 mg, VB1 18 mg, VB2 aspects of the husbandry during the last two decades 35 mg, VB6 18 mg, calcium pantothenate 60 mg, niacin 200 mg, biotin (Zhang et al., 2008; Mou et al., 2011a) and some 2.5 mg, VB 12 0. 6 mg folic acid 6 mg, inositol 1 000 mg, VC 500 mg, VD3 2 000 IU, VK 7 mg. advances have been made in determining the nutritional requirements of this species (Lee et al., become endangered (Xia et al., 2006). The decline of 2001). However, little is known about the infl uence of the wild population and the increased demand for ration level on the growth and energy budget of salmonid products has led to an increase in lenok juvenile lenok. aquaculture in China (Bai et al., 2007). Unfortunately, Our objective was to evaluate the effect of ration problems such as low survival rates and low growth level on growth, feed utilization, and the energy rates during large-scale artifi cial production of lenok budget of the lenok. Additionally, we obtained fi ngerlings have hindered the industrialization, information about the growth characteristics and commercialization, and conservation of this species. energy strategy of this species. Our results provide Our previous research demonstrated that the rearing insight into ways to improve the husbandry of this period is relatively long for fi ngerlings (from 0.5 to species by using an optimal feeding strategy and 10.0 g), lasting about 3 months at temperatures of provide guidelines for the management of stock between 10 and 15°C (Mou et al., 2011b). enhancement in natural aquatic communities based Ration level (RL) has a signifi cant effect on fi sh on the energy fl ow between trophic levels. growth (Cui and Wootton, 1988). A typical growth- ration relationship for fi sh is represented by a 2 MATERIAL AND METHOD decelerating curve (Brett and Groves, 1979; Han et 2.1 Fish and rearing conditions al., 2004; Khan and Abidi, 2010), but studies have also shown that linear relationships are common Juvenile lenok were obtained from the Coldwater (Sullivan, 1982; Cui et al., 1996; Zhang et al., 2011). Fisheries Hatchery Farm at the Heilongjiang Fisheries LIU et al.: Growth and energy budget of juvenile lenok

Research Institute, China. The juveniles were content in the diet and feces were determined as transported to indoor rearing tanks (approx. capacity: described by Furukawa and Tsukahara (1966). 500 L) and acclimated for 2 weeks. During Dissolved oxygen was measured using the iodometric acclimation, the fi sh were fed twice a day (at 09:00 method, and ammonia-N was determined by Nessler’s and 16:00) with a diet designed for this experiment reagent spectrophotometry. For each sample, at least (Table 1) at a ration level of about 4% body weight two determinations were carried out. per day (bwd; based on initial mean body weight). The energy budget was calculated using the The diet was formulated to contain 46% crude protein approach described by Elliott (1976). The terminology and 12% crude lipid, with 1% Cr2 O 3 added as an and symbols for the energy budget followed those indicator for the determination of digestibility. The proposed by the NRC (1981) and Xie et al. (2011): feed was extruded into 2-mm (diameter) pellets, The gross energy intake (IE) and fecal energy (FE) oven-dried at 60°C, and then stored at 4°C. were determined directly. The excretory (non-fecal) The experiment was conducted in a recirculation energy loss is the product of branchial energy (ZE) system consisting of 15 glass aquariums with electric plus urine energy (UE) and was calculated from the heaters (60 cm×60 cm×50 cm, approx. capacity: formula: ZE+UE=24.83(NI–NF–Nr) (where NI is 125 L). The water fl ow rate through each aquarium gross nitrogen intake, NF is fecal nitrogen, and Nr is was about 600 L/h. During the experiment, aeration recovered nitrogen). Growth, in terms of recovered was provided continuously, dissolved oxygen was energy (RE), was calculated from the fi nal and initial maintained at above 8 mg/L, pH was approximately body weight values and the energy content of the 7.5, the water temperature was 16±0.5°C, ammonia-N specimens. Heat production (HE) from metabolism levels were <0.15 mg/L, and the photoperiod was set was calculated as the difference in the energy budget. at 12L:12D. Metabolizable energy (ME) was calculated as: ME=100–FE–(ZE+UE). 2.2 Experimental design 2.4 Statistical analysis Five ration levels were tested: starvation, 2%, 3%, and 4% of the initial body weight per day, and Statistica 6.0 for Windows was used for data satiation. The experiment was conducted in triplicate analysis. We tested for differences in mean values for each ration level. Fish were fed twice a day (at between groups using one-way ANOVA followed by approximately 09:00 and 16:00). Before beginning Duncan’s multiple range test. Differences were the experiment, fi sh were deprived of feed for 24 h. considered signifi cant at P< 0.05. A logarithmic model Twenty fi sh (3.06±0.13 g/fi sh) were collected was used to describe the growth-ration relationship. randomly from the original batch and transferred into each aquarium and an additional 20 fi sh were sampled 3 RESULT to measure initial body composition. During the 3.1 Growth performance experiment, daily feed intake was recorded and uneaten feed was siphoned 20 min after feeding, then The specifi c growth rate for wet weight (SGRw ), dried and weighed. Feces were collected by siphoning dry weight (SGRd ), protein (SGRp ), and energy twice a day. Only feces that remained intact were kept (SGR e ) increased logarithmically with increased for chemical analysis. The trial lasted for 21 d. At the ration levels in juvenile lenok. The mean values of the end of the experiment, the fi sh in each aquarium were SGR at different ration levels are shown in Table 3. batch weighed after a 24-h period of food deprivation The relationships between SGR and RL were and survival rates were calculated. Five fi sh from characterized by decelerating curves (Fig.1) described each aquarium were sampled for chemical analysis. by the following formulae: SGR =-1.417+3.166ln(RL+1) ( R2 =0.994, n =15) 2.3 Chemical analysis w 2 SGR d =-3.367+4.541ln(RL+1) ( R =0.995, n =15) The feed and fi sh samples were analyzed for crude SGR =-3.041+4.387ln(RL+1) ( R2 =0.994, n =15) protein, lipid, ash, and energy content. Chemical p 2 analyses of the experimental feed and lenok samples SGR e =-4.017+5.123ln(RL+1) ( R =0.995, n =15) . were conducted using standard AOAC (1990) As the ration level increased, the feed effi ciency methods. Gross energy was determined using a bomb ratio measured in terms of wet weight (FERw) fi rst calorimeter (HWR-15E, Shanghai, China). The Cr2 O 3 increased, then decreased at higher rations (Table 3). CHIN. J. OCEANOL. LIMNOL.,

5 6 a b SGR =-1.417+3.166 ln(RL+1) 5 SGR =-3.367+4.541 ln(RL+1) 4 W ○○○ d R2 =0.994, n=15 4 R2 =0.995, n=15 ○○○ 3 ○ ○ ○ 3 ○ ○○ ○ 2 ○ 2 ○○ ○ (%d)

○ (%d) ○ W ○ d 1 ○ 1 0 SGR SGR 0 -1 -2 -1 ○ -3 ○ -2 -4 012345 012345 RL (% body weight/d) RL (% body weight/d) 6 6 a d 5 SGR =-3.041+4.387 ln(RL+1) SGR =-4.017+5.123 ln(RL+1) ○ p e ○ ○ 2 4 2 4 R =0.994, n=15 ○ ○ R =0.995, n=15 ○○ ○ 3 ○ ○○ ○ 2 ○ 2 ○○ ○○ ○ ○

(%d) ○

p ○ 1 (%d) 0 e 0 SGR SGR -2 -1 -2 -4 ○ -3 ○ -4 -6 012345 012345 RL (% body weight/d) RL (% body weight/d) Fig.1 Relationships between ration level (RL) and the specifi c growth rate of juvenile Brachymystax lenok in terms of (a) wet

weight (SGRw ), (b) dry weight (SGR d ), (c) protein (SGRp ), and (d) energy (SGR e )

Table 3 Effect of ration level on growth and feed utilization in juvenile Brachymystax lenok (mean±SD)

Ration (% BW per day) FR (% per day) SGRw FERw (%) FER e (%) PRE (%) Starvation -1.33±0.05a 2 1.68±0.01a 1.55±0.09b 91.32±5.74a 16.63±4.89a 22.01±4.47a 3 2.31±0.03b 2.25±0.12c 95.62±6.12ab 21.74±1.46ab 30.70±2.01b 4 2.81±0.02c 2.90±0.04d 100.11±1.71b 26.92±1.93 b 35.83±2.06c Satiation 4.33±0.09d 4.01±0.04e 87.46±2.30 a 25.63±1.88 b 29.81±0.51b

Values with different superscripts in the same column are signifi cantly different from each other (P <0.05). FR: actual feeding rate (%/d)=total feed intake×100/

(((initial body weight +fi nal body weight)/2)×feeding days); SGRw: specifi c growth rate in wet weight (%/d)=100(ln (fi nal body weight)–ln(initial body weight))/d; FERw: feed effi ciency ratio in wet weight (%)=100 wet weight gain/total feed intake; FERd: feed effi ciency ratio in dry weight (%)=100 dry weight gain/total dry feed intake; PRE: protein retention effi ciency (%)=protein gain in fi sh body×100/protein intake.

The highest effi ciency was observed at a 4% ration The relationship between digestible energy (DE) ( P<0.05). However, there was no signifi cant difference intake and energy gain expressed per unit metabolic in FERw between the 3 and 4% ration (P >0.05). The body weight of kg-0.80 (Brett and Groves, 1979) was relationships between RL and FERw or feed effi ciency described by a linear equations as follows: ratio measured in terms of energy (FER ) are shown e y =-52.274+0.496 x ( R2 =0.936, n =15), in Figs.2 and 3. The protein retention effi ciency (PRE) was where x is DE fed and y is energy retained. signifi cantly higher at the 4% ration and signifi cantly For zero retention (y =0) the required intake of DE lower at 2% ration than other groups (P< 0.05) could be calculated using the above equation as (Table 3). 52.274/0.496=105.39 kJ BW (kg) -0.80/d, the utilization LIU et al.: Growth and energy budget of juvenile lenok

Table 4 Effect of ration level (RL) on the body composition (wet-weight basis) of juvenile Brachymystax lenok (mean±SD)

Ration (% BW per day) Body water (%) Protein (%) Lipid (%) Ash (%) Energy (KJ/g) Starvation 87.01±0.51a 9.21±0.17a 1.36±0.04a 2.49±0.02a 2.34±0.01 a 2 82.00±0.96 b 12.78±0.29b 2.43±0.08bc 2.14±0.07b 3.85±0.21 b 3 81.42±0.05b 13.09±0.18c 2.45±0.05cd 2.10±0.08b 3.93±0.09 b 4 80.33±0.47c 13.31±0.04c 2.69±0.18d 2.16±0.01b 4.25±0.11 c Satiation 79.52±0.31c 13.41±0.14c 3.66±0.21e 2.03±0.09 b 4.50±0.16 d

Values with different superscripts in the same column are signifi cantly different from each other (P <0.05).

Table 5 Effect of ration level on the apparent digestibility coeffi cient of juvenile Brachymystax lenok (mean±SD)

Ration (% BW per day) 2 3 4 Satiation

a a a a ADCd 65.96±2.54 62.35±3.38 61.39±3.49 60.59±1.49

a a a a ADCp 87.99±0.90 87.92±1.09 89.58±0.94 89.36±0.40

a ab b c ADCe 79.60±1.52 76.33±2.13 74.49±2.30 70.97±1.10

Means with different superscripts are signifi cantly different from each other (P <0.05). ADCd: apparent digestibility coeffi cients of dry matter (%)=100(1–

Cr 2 O 3 in the diet/Cr2 O 3 in the feces); ADCp: apparent digestibility coeffi cients of crude protein (%)=100(1–Cr2 O 3 in the diet/crude protein content in feces/

(Cr 2 O 3 in the feces×crude protein in the diet)); ADCe: apparent digestibility coeffi cients of gross energy (%)=100(1–Cr2 O 3 in the diet×gross energy content in feces/(Cr2 O 3 in the feces×gross energy in the diet)).

Table 6 Effect of ration level on the energy budget of juvenile Brachymystax lenok (mean±SD)

Ration (% BW/d) IE (J/g/d) RE (%) HE (%) FE (%) ZE+UE (%) Starvation -128.19 115.08 13.11 2 273.40 19.14±1.02 a 54.39±0.70 a 20.40±1.52 a 6.08±0.41 a 3 375.75 21.74±1.46a 48.11±0.04 b 24.64±1.29b 5.50±0.13bc 4 458.20 26.92±1.93 b 42.35±2.63c 25.51±2.30b 5.22±0.22cd Satiation 705.47 25.63±1.88b 39.56±2.92 d 29.03±1.10c 5.78±0.06 ab

Values with different superscripts in the same column are signifi cantly different from each other (P <0.05). IE: gross energy intake; FE: fecal energy; ZE+UE: excretory (non-fecal) energy loss; HE: heat production; RE: recovered energy. In the starvation group, ZE+UE, HE, and RE are expressed as J/g/d. effi ciency of DE for growth was defi ned by the slope (ADCe) decreased with increased RL (P <0.05). In of the lines with a value of 0.496. contrast, RL had no effect on ADCd and ADCp (ADC of dry matter and protein) (P >0.05) (Table 5). 3.2 Body composition 3.4 Energy budget The water content of juvenile lenok decreased as RL increased and was signifi cantly higher in the The energy budgets at different ration levels for starvation group than in the other groups (P <0.05) juvenile lenok are shown in Table 6. The proportion (Table 4). Protein and lipid content increased with of energy intake lost in fecal production (FE) tended increased RL and were signifi cantly lower in the to increase with an increase in RL (P< 0.05). There starvation group than in the other groups (P< 0.05). was a signifi cant decrease in the proportion of feed Ash content was signifi cantly lower in the starvation energy used for excretion (ZE+UE) as RL increased group than the other groups (P <0.05), but there was from 2 to 3 and 4% ration (P <0.05), but no change no difference between the remaining groups (P >0.05). between the 2% and satiation rations. The proportion Energy content increased with increased RL, and was of feed energy used for heat production (HE) signifi cantly lower in the starvation group than in the decreased with increased RL and was lowest in fi sh other groups and signifi cantly higher in the satiation fed a satiation ration (P <0.05). There was an increase group than in the remaining groups (P< 0.05). in the proportion of retention energy (RE) from 2 to 3 and 4% ration, and then decrease at satiation (P <0.05). 3.3 Apparent digestibility The energy budget for juvenile lenok at satiation was: The apparent digestibility coeffi cient of energy 100IE=29.03FE+5.78(ZE+UE) +39.56HE+25.63RE. CHIN. J. OCEANOL. LIMNOL.,

105 4 DISCUSSION ○○ 100 ○RL=2.89 ○ Previous studies have reported two main types of 95 ○ ○ growth-ration relationships: a simple linear regression ○ (Niimi and Beamish, 1974; Cui et al., 1996; Zhang et 90 ○ , %) ○○

W al., 2011) and, more commonly, an increasing but 85 2 ○ FERW =53.270+31.622×RL–5.472×(RL) ○ decelerating curve (Jobling, 1994; Han et al., 2004; (FER R2 =0.606, n=15 Khan and Abidi, 2010). In the present study, the 80 growth-ration relationship over the whole ration 75 Feed efficiency ratio in wet weight Feed efficiency range was represented by a decelerating curve and the conversion effi ciency was highest at an intermediate 70 1.5 2 2.5 3 3.5 4 54.5 ration level. The model defi ned as SGR= a + b ln(RL+1) Ration level (RL, % body weight/d) (where SGR is specifi c growth rate, RL is ration level, Fig.2 Relationship between feed effi ciency ratio in terms and a and b are constants) best described the growth- of wet weight (FERw, %) and the ration level (RL) in ration relationship for juvenile lenok. This is Brachymystax lenok consistent with observations in brown trout Salmo trutta (Elliott, 1975), which also exhibits a decelerating 30 curvilinear pattern for the growth-ration relationship, 28 RL=3.53 but differs from that in a study by Han and Wang 26 (1990), in which the growth-ration relationship was 24 linear. This discrepancy is most likely the result of 22 two factors. First, the latter experiment used live , %) e 20 Gammarus pulex (energy value: 0.847 4 kcal/g),

(FER 18 whereas we used formulated feed in the current study.

FER =-14.167+23.793×RL–3.367×(RL)2 e Formulated feed has a higher energy density than live 16 R2=0.715, n=15 food. Therefore, lenok juveniles fed on formulated

Feed efficiency ratio in energy Feed efficiency 14 feed may have a higher maximum ration in terms of 12 energy than those fed on live food, resulting in 10 reduced food conversion effi ciencies at high rations. 1.5 2 2.5 3 3.5 4 4.5 5 Ration level (RL, % body weight/d) This hypothesis is partly supported by results from two studies on grass carp, Ctenopharyngodon idella , Fig.3 Relationship between feed effi ciency ratio in terms (Cui et al., 1992) and white sturgeon, Acipenser of energy (FERe, %) and ration level (RL) in Brachymystax lenok transmontanus , (Cui et al., 1996). The growth relationships were characterized by a decelerating 160 curve when fed on dry feed, but were linear when fed 140 on natural food with a much lower energy density. 120 Second, the water temperature was much lower 100 (8±1°C) in Han and Wang’s experiment (1990) than /d) 80 -0.80 in our study (16±0.5°C). Research on summer 60 fl ounder, Paralichthys dentatus , suggests that the 40

20 growth-ration relationship is linear at lower 0 temperatures, but curvilinear at higher temperatures -20 (Malloy and Targett, 1994). -40 The feed effi ciency ratio was highest at an Energy retention (kJ kg Energy -60 intermediate ration level. This is consistent with -80 observations in other studies in which the growth- -100 0 50 100 150 200 250 300 350 400 ration relationship was curvilinear (Brett and Groves, DE fed (kJ kg-0.80/d) 1979; Jobling, 1994; Sun et al., 2006). However, the optimum RL (=2.89% bwd) based on the relationship Fig.4 Daily energy retention per unit metabolic weight of kg- 0.80 in Brachymystax lenok fed increasing levels of between RL and FERw (Fig.2) was different from the DE optimum RL (=3.53% bwd) based on the relationship LIU et al.: Growth and energy budget of juvenile lenok

between RL and FERe (Fig.3). The difference is most 1997; Tang et al., 2003; Liu et al., 2012). Further likely the result of the body water content in the fi sh. study is required to quantify these effects for lenok. The feed effi ciency ratio calculated on a wet weight For stock enhancement of wild populations, the basis is subject to the infl uence of fi sh body water growth-ration relationship is important in evaluating content. However, the feed effi ciency ratio in energy energy between trophic levels so as to identify optimal units (FERe) is not affected by fi sh body water content, stocking sites and capacity based on food abundance life stage, or trial period. (Kelso, 1972; Huisman, in natural habitats. Additionally, the growth-ration 1976; Verreth and den Bieman, 1987; Han et al., relationship has important implications for fi sh 2004). aquaculture. For species that exhibit a curvilinear The proportion of feed energy used for excretion growth-ration relationship, the optimum feeding ranged from 5.22% to 6.08%, which was within the strategy would be an intermediate ration, where feed range of mean values of 5%–6.8% in other studies effi ciency is maximized. For species with a linear (Winberg, 1956; Brafi eld, 1985), but lower than that growth-ration relationship, the optimum feeding reported for brown trout (mean value of 8%) (Elliott, strategy would be a satiation ration, where both feed 1976). As ration levels increased, the proportion of effi ciency and growth rates are maximized (Xie et al., feed energy used for growth increased and then 1997). In the present study, the growth-ration decreased, while the heat production from feed energy relationship we observed suggests that the optimum decreased. This may have been due to an increase in feeding strategy for large-scale, controlled seed specifi c dynamic action (SDA) at a higher ration level production of lenok at this growth stage would be a (Han et al., 2004). The energy budget of juvenile sub-maximum ration with formulated feed. The most lenok fed at the maximum ration was: suitable feeding rate is 2.89% bwd in terms of wet 100ME=60.68HE+39.32RE (calculated from Table weight growth, or 3.53% bwd in terms of energy 5). The assimilation was similar to values of 60%– growth. However, we caution that the values expressed 90% reported in salmonids fed on formulated diets as % growth rate and % feed ration may differ for (Cho et al., 1982). Cui and Liu (1990) calculated a different size fi sh. Additionally, when using a different mean energy budget based on 14 previously published feed formulation or live feed the % intake and SGR budgets for fi sh fed on maximum rations: values are likely to differ. In this study, we attempted 100ME=60HE+40RE, where ME is metabolizable to translate feed ration and subsequent growth into energy, which is calculated as ME=ZE–FE–(UE+ZE). absolute values. Instead of describing feed ration (as Our results suggest that lenok have moderate % intake of biomass) and growth in SGR, the total metabolism and moderate growth. This differs from budget was presented as per unit metabolic body the pattern of lower metabolism and higher growth weight kg -0.80 . Using this information, energy intake observed in cutthroat trout Salmo clarki (Brocksen et can be plotted against energy gain yielding a better al., 1968), rainbow trout Salmo gairdneri (From and estimation of maintenance ration and effi ciency for Rasmussen, 1984; Christian, 1987), and mandarin growth. The maintenance requirement for energy of fi sh Siniperca chuatsi (Liu, 1998); and also differs juvenile lenok was 105.39 kJ BW (kg)-0.80 /d , the from the pattern of higher metabolism and lower utilization effi ciency of DE for growth was 0.496. growth in Nile tilapia Oreochromis niloticus (Xie et These values are of more use for practical applications al., 1997), Gibel carp Carassius auratus gibelio (Zhu in aquaculture. et al., 2000), and grass carp Ctenopharyngodon idella (Cui et al., 1992). There are two possible reasons for 5 ACKNOWLEDGMENT this difference. First, lenok are a coldwater carnivorous fi sh that typically feed on trichoptera larvae, terrestrial Thanks to all colleagues who participated in rearing invertebrates, and fi sh, a diet that differs from that of management for lenok. most piscivorous fi sh species (Nakano, 1999). Second, lenok exhibit a moderate activity level, which References can have a considerable effect on energy allocation Alekseyev S S, Kirillov A F, Samusenok V P. 2003. Distribution (Calow, 1985). However, for a given fi sh species, and morphology of the sharp-snouted and the blunt- many factors can signifi cantly affect the energy snouted lenoks of the Brachymystax () distribution, including feed quality, water temperature, of East . Journal of Ichthyology , 43 : 350-373. and experimental method (Jobling, 1994; Xie et al., AOAC. 1990. Offi cial Methods of Analysis (15th edn). CHIN. J. OCEANOL. LIMNOL.,

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