Effects of salinity and dietary carbohydrate levels on growth and energy budget of juvenile Litopenaeus vannamei.

ABSTRACT The culture of Litopenaeus vannamei in low-salinity waters is now popular in many regions of the world, A 6 x 3 factorial experiment was conducted to determine the effects of salinities (tap water, 1 [per thousand], 2 [per thousand], 4 [per thousand], 8 [per thousand], and 16 [per thousand]) and dietary carbohydrate levels (15.47%, 29.15%, and 41.00%) on survival, growth, food consumption, food efficiency, absorption efficiency, and energy budget of juvenile L. vannamei. The results showed that no shrimp survived in tap water at the end of the experiment irrespective of dietary carbohydrate (CBH). At each dietary CBH level, the specific growth rate (SGR), food consumption, and food efficiency generally increased with increasing salinity within the range of 1-16 [per thousand]. At salinities of 1 [per thousand], 2 [per thousand], 4 [per thousand], 8 [per thousand], and 16 [per thousand], optimal CBH levels corresponding to maximum SGR decreased with increasing salinity and were 29.87%, 27.59%, 26.85%, 26.25%, and 22.29%, respectively. At 1-8 [per thousand], the percentage of consumed energy deposited in growth (%C) was significantly higher in shrimps fed 29.15% CBH as compared with other treatments, whereas at 16 [per thousand], the significantly higher value was in those fed 15.47% CBH.

KEY WORDS: Litopenaeus vannamei, salinity, carbohydrate, growth, energy budget

INTRODUCTION

The shrimp-farming industry is currently experiencing major crop losses due to disease outbreaks sometimes associated with the deterioration of water quality, which makes the establishment of saltwater ponds economically risky. Instead, the culture of penaeid shrimp in low-salinity waters, which not only provides a cost-effective solution to prevalent disease problems but also improves the use of saline-alkaline land waters, is now popular in many regions of the world (Bray et al. 1994; Dong 2003). The Pacific white shrimp Litopenaeus vannamei (Boone, 1931) possesses the ability to tolerate low salinities. Recently, there has been increasing interest in the culture of this species in low salinity waters or fresh water (Saoud et al. 2003), for which information is required on the effects of salinity on performance, principally growth and survival. A reduction in salinity may modify the osmotic and ionic balances in shrimp. To recover the normal balances, the shrimp may have to expend a considerable amount of energy, resulting in less energy to spare for growth (Bindu & Diwan 2002; Zhang & Dong 2002).

In general, glucose is one of the main energetic substrates for general metabolic processes in crustaceans (Hu 1958). In a recent study, Rosas et al. (2000) reported that Litopenaeus stylirostris can use the gluconeogenesis pathway according to dietary carbohydrate availability, with a higher gluconeogenic activity in shrimps fed diets containing comparatively low amounts of carbohydrate and low or no gluconeogenic activity in shrimps fed diets containing more than 20% carbohydrate. This better efficiency of using carbohydrate for routine metabolism, thus liberating protein for tissue aggregation, was also reported in L. vannamei (Dokken 1987). Penaeus monodon (Alava & Pascual 1987), and Penaeus indicus (Ali 1982).

Taking into account the energy consumption required for osmoregulation of L. vannamei adapting to low salinity conditions (Bindu & Diwan 2002), it is possible that carbohydrate metabolism adaptation takes place. This study was designed to determine the effects of tap water (about 0.2 [per thousand] salinity) and low salinities (1 [per thousand], 2 [per thousand], 4 [per thousand], 8 [per thousand], and 16 [per thousand]) on growth of juvenile L. vannamei fed three levels of dietary carbohydrates (15.47%, 29.15%, and 41.00%), together with an analysis of the bioenergetic mechanisms involved.

MATERIALS AND METHODS

Diet Preparation

Three approximately isoenergetic diets were formulated, containing 15.47%, 29.15%, and 41.00% of carbohydrate. The diets were prepared by mixing dry ingredients and water (2:1, w/w), and pellet-type diets were produced through a meat grinder with a 1.6 mm die. The diets were then oven-dried (70[degrees]C for 12 h) to 6-7% moisture and stored at 4[degrees]C until used. The formulation and proximate composition of the experimental diets are shown in Table 1.

Source and Acclimation of Experimental Shrimp

The experiment was carried out at the Laboratory of Aquaculture Ecology, Ocean University of China, Qingdao, P.R. China. L vannamei juveniles were obtained from Hainan Shrimp Breeding Farm, Hainan, P.R. China. The shrimp were initially held in six fiberglass tanks (200 x 80 x 60 cm) at 31 [per thousand], for three days and were acclimated to six salinity levels (16 [per thousand], 8 [per thousand], 4 [per thousand], 2 [per thousand], 1 [per thousand], and tap water) by lowering the salinity at a rate of 5 [per thousand] [d.sup.-1] by adding tap water (about 0.2 [per thousand] salinity).

Experimental Design

A two-factor factorial experimental design (6 x 3) with three replications per treatment was followed. A static-water system consisting of 54 aquaria (45 x 30 x 30 cm, water volume 35L) with aeration was used. After 24 h feed deprivation, 48 shrimp with weight range from 0.625 g to 0.645 g were selected from the acclimating fiberglass tanks. From the 48 shrimp, three groups of tour shrimps each were randomly sampled for analysis of initial energy content and nitrogen content at the corresponding salinity level. The remainder (36 shrimp) were randomly stocked into nine aquaria with each aquarium holding four shrimps. The experiment lasted for five weeks. Shrimp were hand-fed an excess ration twice daily (at 06:00 and 18:00 h) for each group. Each meal lasted approximately 2.5 h, and any uneaten food was collected and dried at 70[degrees]C. Twice a day, intact feces and molts were collected from each aquarium, freeze-dried immediately, and held at 20[degrees]C until analyzed. For each aquarium, two-thirds of the water was replaced daily. During the experiment, dissolved oxygen was maintained above 6.0 mg/L, water temperature at 25 [+ or -] 0.5[degrees]C, pH from 7.7 to 8.2, and the photoperiod was 14L:10D.

Calculation of Data

Specific growth rate (SGR), food efficiency (F[E.sub.f]), energy conversion efficiency (F[E.sub.e]), and absorption efficiency (AE) were calculated as follows:

SGR = 100 x (ln[W.sub.2] - ln[W.sub.1])/t

F[E.sub.f] = 100 x ([W.sub.2] - [W.sub.1])/[C.sub.w]

F[E.sub.e] = 100 x ([E.sub.2] - [E.sub.1])/[C.sub.e]

AE = 100 x ([C.sub.w] - [F.sub.d])/[C.sub.w]

where [W.sub.2] and [W.sub.1] are the final and initial wet weights of the shrimp, [E.sub.2] and [E.sub.1] are the final and initial energy contents of the shrimp, [C.sub.w] is the food consumption in dry weight, [C.sub.e] is the consumed energy, [F.sub.d] is the fecal production in dry weight, and t is the duration of the experiment.

The energy budget equation of L. vannamei juveniles can be defined through the construction of a budget in which the consumed energy (C) is partitioned between growth (G), respiration (R), excretion (U), feces (F), and exuviae (E), i.e., C = G + R + U + F + E. The gross energy contents of diet, shrimp, feces, and molt were measured with a 1281 Oxygen Bomb Calorimeter (Parr Instrument, Moline, Illinois). The initial energy contents of the shrimp were assumed to be equal to the average energy value of the shrimp sacrificed at the beginning of the experiment.

Preliminary experiment indicated that nitrogen in L. vannamei juveniles was mainly excreted as ammonia, with only very small amounts of urea and uric acid that might be negligible. The excretory nitrogen is converted into energy using the equivalent of 24,830 Jx[g.sup.-1] N for nitrogen excreted (Elliott 1976). Hence, the energy lost as U can be calculated using the equation:

U = ([C.sub.N] - [G.sub.N] - [F.sub.N] - [E.sub.N]) x 24,830

where [C.sub.N], [G.sub.N], [F.sub.N], and [E.sub.N] represent the nitrogen contents of diet, shrimp, feces, and molt, respectively. The nitrogen contents of diet, shrimp, feces, and molt were measured with a PE-240 element analyzer (Beijing NCS Analytical Instrument Company, Beijing, China). The initial nitrogen contents of the shrimp were assumed to be equal to the average nitrogen value of the shrimp sacrificed at the beginning of the experiment.

The energy lost as R can he calculated using the equation:

R = C - G - F - E - U

Statistical Analysis

Data from each treatment were subject to a two way ANOVA. When overall differences were significant at less than the 5% level, Tukey's test was used to compare the mean values between individual treatments. The square-root transformation of the sine-arc before analyzing the values given in percentages was used. Statistical analysis was performed using SPSS (statistic package for social science) 10.0.

RESULTS

Growth

All shrimps survived at 4, 8, and 16 [per thousand], whereas no shrimps survived in tap water (about 0.2 [per thousand] salinity) at the end of the experiment, irrespective of dietary carbohydrate (CBH). Hence, analysis of the respective dependable variable of shrimps maintained in tap water was excluded from the experiment except for concerning the survival. Within the range of 1-2 [per thousand], the survival increased with increasing dietary CBH from 15.47% to 41.00%, and at each CBH level, the survival in shrimps maintained at 2 [per thousand] was slightly higher than those maintained at 1 [per thousand]. At each dietary CBH level, the specific growth rate (SGR), food consumption (FC), and food efficiency (F[E.sub.f]) generally increased with increasing salinity from 1 [per thousand] to 16 [per thousand], and the highest values were obtained in those maintained at 16 [per thousand] (Table 2 and Fig. 1).

A two-way ANOVA showed that salinity, dietary CBH, and the interaction between salinity and dietary CBH had significant effects on survival, SGR, FC, and F[E.sub.f], but none for absorption efficiency (AE). The relationship between SGR, FC or F[E.sub.f], salinity, and dietary CBH is shown in Table 3.

In the 16 [per thousand] groups, SGR and FC were similar in shrimps fed 29.15% and 15.47% dietary CBH, whereas those fed 41.00% dietary CBH exhibited a significantly lower value. In the 1-8 [per thousand] groups, SGR and FC in shrimps fed 29.15% dietary CBH were significantly higher as compared with other treatments (Fig. 1 and Table 2). The relationship between SGR and dietary CBH is shown in Table 4. Quadratic regression analysis indicated that the optimal CBH corresponding to maximum SGR decreased with increasing salinity from 1 [per thousand] to 16 [per thousand] and were 29.87%, 27.59%, 26.85%, 26.25%, and 22.29% at salinities of 1 [per thousand], 2 [per thousand], 4 [per thousand], 8 [per thousand], and 16 [per thousand], respectively.

Energy Budget

The pattern of energy allocation varied with salinity and dietary CBH, in which 67.90-80.24% of consumed energy was lost through respiration, 7.25-18.14% invested in growth, 5.21-5.99% for feces, 3.87-8.73% for excretion, and only 0.69-0.73% for exuviae (Table 5). At each dietary CBH level with increases of salinity within the range of 1-16 [per thousand], the consumed energy and the percentage of consumed energy invested in growth (%C) exhibited increasing trends while that lost in respiration and excretion (%C) exhibited decreasing trends. At 16 [per thousand], the percentages of respiration and excretion (%C) were lowest of all while the consumed energy was highest of all; thus energy conversion efficiency was highest of all.

A two-way ANOVA showed that salinity, dietary CBH, and the interaction between salinity and dietary CBH had significant effects on growth, respiration, and excretion (%C), but none for feces and exuviae (%C). The relationship between growth, respiration or excretion (%C), salinity, and dietary CBH is shown in Table 3.

At 1-8 [per thousand], the percentage of consumed energy deposited in growth (%C) was significantly higher in shrimps fed 29.15% CBH as compared with other treatments, whereas at 16 [per thousand], the significantly higher value was in those fed 15.47% CBH (Table 5). The relationship between growth (%C) and CBH is shown in Table 4. Quadratic regression analysis indicated that the optimal CBH corresponding to maximum percentage in growth (%C) decreased with increasing salinity from 1 [per thousand] to 16 [per thousand], and was 29.36%, 26.75%, 26.50%, 26.40%, and 18.43% at salinities of 1 [per thousand], 2 [per thousand], 4 [per thousand], 8 [per thousand], and 16 [per thousand], respectively.

DISCUSSION

Salinity Effect on Growth of L. vannamei juveniles

A reduction in salinity can significantly affect the survival and growth of penaeid shrimps, although they possess the ability to tolerate low salinities (Huang 1983, Bray et al. 1994). Galli & Stern (1998) reported that the survival of L. vannamei was drastically reduced when salinity decreased below 0.18 [per thousand]. Bray et al. (1994) reported that L. vannamei juveniles had growth optima between 5 [per thousand] and 15 [per thousand]. Currently, no shrimps survived in tap water (about 0.2 [per thousand], salinity), the survival increased with increasing salinity from 1 [per thousand] to 2 [per thousand], and they grew well in salinities [greater than or equal to] 4 [per thousand], indicating the limited capability for L. vannamei juveniles to tolerate very low salinities. It was apparent from the experiment, however, that salinity had significant effects on both growth and food efficiency. At each dietary carbohydrate level, the maximum specific growth rate and food efficiency were obtained in shrimp maintained at 16 [per thousand] and diminished with a reduction in salinity: the shrimps maintained at 1-2 [per thousand] exhibited significantly lower values. Hence, at salinities [less than or equal to] 16 [per thousand], decreasing salinity significantly affected the growth rate of L. vannamei juveniles and even endangered their survival.

The growth rate of the shrimp seems to have a direct relation with food consumption, changes of which may reflect the adaptation to various environmental conditions. Previous studies had shown that holding penaeid shrimps at salinities near isosmotic points could result in an increase of food consumption (Staples & Heales 1991). Rosas et al. (2001a) reported that L. vannamei juveniles maintained at 15 [per thousand] salinities consumed 1.69 times more food than those at 5 [per thousand]. Similarly, in the present study, food consumption generally increased with increasing salinity within the range of 1-16 [per thousand] with the maximum value at 16%c, which coincided with the salinity at which the highest specific growth rate was observed, indicating that at salinities [less than or equal to] 16 [per thousand], holding L. vannamei juveniles at salinities closer to isosmotic points could result in increased appetite.

The isosmotic point for penaeids ranged from 23 to 30 ppt (Dall 1981; Castille & Lawrence 1981). It is generally believed that shrimps near the isosmotic point expend the least energy on respiration and excretion, and so they exhibit the best growth rate and the most efficient energy conversion (Panikkar 1968). By contrast, when shrimps are under anisosmotic conditions, additional energy is required to meet the osmotic adjustments, which generally increase as a function of deviations in salinity from the isosmotic zone; that is, when the concentration gradient between ambient salinity and body fluids increases, more energy is expended for recovery of homeostasis and, as a result, less energy is available for growth (Zhang & Dong 2002: Bindu & Diwan 2002). In the present study, as the range of salinity tested deviated from the isosmotic point, the energetic demand on maintaining homeostasis, i.e., the percentages of energy lost to respiration and excretion (%C), increased with decreasing salinity from 16 [per thousand] to 1 [per thousand].

The results obtained in our work provide evidence that the growth differences between salinities are primarily the consequence of variations in both food consumption and energy allocation. Food consumption and energy gain (the percentage of energy invested in growth, %C) of L. vannamei juveniles appeared to increase with increased salinity within the range of 1-16 [per thousand], whereas total metabolic expenditure (the percentages of energy lost to respiration and excretion, %C) displayed inverse trends with salinity. Thus, the enhanced growth of L. vannamei juveniles with increasing salinity from 1 [per thousand] to 16 [per thousand] was mainly due to the significantly increased food consumption associated with the significantly decreased proportion of energetic cost for osmotic regulation. At 16 [per thousand], the food consumption was highest of all while the proportion of energy losses was least of all, and consequently, the growth rate was highest of all. By contrast, previous investigations suggested that the depression of growth for the shore crab Carcinus maenas, the common carp Cyprinus carpio, and the blue crab Callinectes sapidus under hypo-osmotic stresses could not be explained with enhanced metabolic demands; rather, this result was a consequence of a significantly reduced assimilation capability (Guerin & Stickle 1992, 1995; Wang et al. 1997; Anger et al. 1998). In the present study, salinity had no significant effects on absorption efficiency and the percentage of fecal production (%C), indicating the different bioenergetic mechanisms by interspecies.

Carbohydrate Effect on Growth of L. vannamei Juveniles at Low Salinities

Carbohydrate is considered the most economical source of dietary energy in penaeid shrimp. Previous investigations on a variety of penaeid species indicated an improved growth on diets with an adequate dietary carbohydrate supply. All (1982) reported that the survival, growth, and food conversion efficiency of juvenile P. indicus increased with an increase in the dietary carbohydrate level from 10-40%. Rosas et al. (2001b) reported that the maximum growth rate for L. vannamei juveniles occurred between 6% and 23% of dietary carbohydrate.

It is generally believed that more energy is expended for osmoregulation by aquatic animals subjected to hypo-osmotic environments as compared with those maintained under isosmotic conditions (Panikkar 1968). Hence, we speculated that maximizing the carbohydrate content relative to protein in diets might promote the growth of penaeid shrimp maintained at low salinities, based on the assumption that diets were formulated to be isoenergetic. In the present study, dietary carbohydrate had significant effects on growth, food consumption, and energy gain (the percentage of energy invested in growth, C%). At 1-8 [per thousand], the specific growth rate in shrimps fed 15.47% dietary carbohydrate was significantly lower than those fed 29.15% dietary carbohydrate; by contrast, at 16 [per thousand], the specific growth rate in shrimps fed 15.47% dietary carbohydrate was not significantly different from those fed 29.15% dietary carbohydrate. The responses of food consumption and energy gain (C%) to dietary carbohydrate were similar to that of the specific growth rate, These results confirmed that carbohydrate was an important source of energy for L. vannamei juveniles maintained at low salinities, and an adequate level of carbohydrate provided in diets could not only significantly improve growth performance of L. vannamei juveniles, but also have a protein sparing action.

TABLE 1.
Ingredient and proximate composition of the experimental diets.

                                   Carbohydrate Level (%)

        Formulation (%)            15.47   29.15   41.00

  Fish meal                        47.5    31      28
  Soybean meal                     20      20       0
  Peanut meal                      20      10       0
  Wheat flour                       0      25      58
  Fish oil                          3       4.5     4.5
  Lecithin                          2       2       2
  Sodium alginate                   1.5     1.5     1.5
  Vitamin mix (1)                   2       2       2
  Mineral mix (2)                   4       4       4
Proximate analysis (%)
  Moisture                          6.51    6.65    6.71
  Protein                          45.31   35.18   26.59
  Lipid                             7.08    7.03    7.07
  Carbohydrate                     15.47   29.15   41.00
  Ash                              13.56   10.67    9.35
  Gross energy (kJ * [g.sup.-1])   17.77   17.54   17.38

(1) Vitamin mix, each 1000 g of diet contained: thiamin-HCl, 60 mg;
riboflavin, 100 mg; folic acid, 10 mg; pyridoxine-HCl, 140 mg; niacin,
400 mg; calcium pantothenate, 140 mg; choline chloride, 4000 mg;
inositol, 4000 mg; ascorbic acid, 4000 mg; biotin, 2 mg; p-amino
benzoic acid, 150 mg; [alpha]-tocopherol, 400 mg; menadione, 34 mg;
cyanocobalamine, 0.8 mg; retinol acetate, 150,000 IU; cholecalciferol,
60,000 IU

(2) Minieral mix, each 1000 g of diet contained:
Ca[([H.sub.2]P[O.sub.4]).sub.2], 8.800 g; CaC[O.sub.3], 8.240 g;
[K.sub.2]HP[O.sub.4], 4.000 g; Na[H.sub.2]P[O.sub.4], 11.200 g;
MgS[O.sub.4] * 7[H.sub.2]O, 5.095 g; KCl, 1.600 g; FeS[O.sub.4]
* 7[H.sub.2]O, 0.400 g; AlCl * 6[H.sub.2]O, 0.016 g; ZnS[O.sub.4] *
7[H.sub.2]O, 0.432 g; MnS[O.sub.4] * [H.sub.2]O, 0.080 g; CuS[O.sub.4]
* 5[H.sub.2]O, 0.008 g; Co[Cl.sub.2] * 6[H.sub.2]O, 0.112 g; KI,
0.016 g; [Na.sub.2]Se[O.sub.3], 0.001 g

TABLE 2.
The effects of salinity and dietary carbohydrate levels
on growth, food consumption, food efficiency and
absorption efficiency of L. vannamei juveniles.

     Treatment

Salinity   Carbohydrate
  (%)          (%)               IW (g)

    1         15.47       0.642 [+ or -] 0.002
              29.15       0.643 [+ or -] 0.002
              41.00       0.642 [+ or -] 0.004
    2         15.47       0.640 [+ or -] 0.004
              29.15       0.636 [+ or -] 0.004
              41.00       0.636 [+ or -] 0.007
    4         15.47       0.632 [+ or -] 0.003
              29.15       0.633 [+ or -] 0.003
              41.00       0.631 [+ or -] 0.006
    8         15.47       0.636 [+ or -] 0.002
              29.15       0.637 [+ or -] 0.003
              41.00       0.634 [+ or -] 0.002
   16         15.47       0.637 [+ or -] 0.002
              29.15       0.636 [+ or -] 0.004
              41.00       0.641 [+ or -] 0.005

     Treatment

Salinity   Carbohydrate
  (%)          (%)               FW (g)

    1         15.47       1.779 [+ or -] [0.063.sup.e]
              29.15       2.560 [+ or -] [0.052.sup.c]
              41.00       2.058 [+ or -] [0.076.sup.d]
    2         15.47       2.240 [+ or -] [0.091.sup.d]
              29.15       2.693 [+ or -] [0.017.sup.bc]
              41.00       2.130 [+ or -] [0.038.sup.d]
    4         15.47       2.598 [+ or -] [0.058.sup.bc]
              29.15       3.386 [+ or -] [0.097.sup.a]
              41.00       2.235 [+ or -] [0.059.sup.d]
    8         15.47       2.779 [+ or -] [0.121.sup.bc]
              29.15       3.447 [+ or -] [0.097.sup.a]
              41.00       2.267 [+ or -] [0.074.sup.d]
   16         15.47       3.487 [+ or -] [0.106.sup.a]
              29.15       3.483 [+ or -] [0.102.sup.a]
              41.00       2.811 [+ or -] [0.103.sup.b]

      Treatment

Salinity   Carbohydrate
  (%)          (%)              Survival (%)

    1         15.47        41.67 [+ or -] [14.43.sup.b]
              29.15        50.00 [+ or -] [25.00.sup.b]
              41.00        83.33 [+ or -] [14.43.sup.a]
    2         15.47        66.67 [+ or -] [14.43.sup.ab]
              29.15        83.33 [+ or -] [14.43.sup.a]
              41.00       100.00 [+ or -] [0.00.sup.a]
    4         15.47       100.00 [+ or -] [0.00.sup.a]
              29.15       100.00 [+ or -] [0.00.sup.a]
              41.00       100.00 [+ or -] [0.00.sup.a]
    8         15.47       100.00 [+ or -] [0.00.sup.a]
              29.15       100.00 [+ or -] [0.00.sup.a]
              41.00       100.00 [+ or -] [0.00.sup.a]
   16         15.47       100.00 [+ or -] [0.00.sup.a]
              29.15       100.00 [+ or -] [0.00.sup.a]
              41.00       100.00 [+ or -] [0.00.sup.a]

     Treatment

Salinity   Carbohydrate
  (%)          (%)                FC (g)

    1         15.47       2.613 [+ or -] [0.156.sup.d]
              29.15       3.437 [+ or -] [0.170.sup.b]
              41.00       2.700 [+ or -] [0.174.sup.d]
    2         15.47       2.713 [+ or -] [0.163.sup.d]
              29.15       3.523 [+ or -] [0.093.sup.b]
              41.00       2.713 [+ or -] [0.042.sup.d]
    4         15.47       3.277 [+ or -] [0.090.sup.bc]
              29.15       4.403 [+ or -] [0.185.sup.a]
              41.00       2.823 [+ or -] [0.105.sup.cd]
    8         15.47       3.543 [+ or -] [0.224.sup.b]
              29.15       4.420 [+ or -] [0.200.sup.a]
              41.00       2.873 [+ or -] [0.161.sup.cd]
   16         15.47       4.390 [+ or -] [0.217.sup.a]
              29.15       4.450 [+ or -] [0.177.sup.a]
              41.00       3.653 [+ or -] [0.214.sup.b]

     Treatment

Salinity   Carbohydrate
  (%)          (%)               F[E.sub.f] (%)

    1         15.47       43.50 [+ or -] [0.45.sup.h]
              29.15       55.77 [+ or -] [0.33.sup.f]
              41.00       52.50 [+ or -] [0.61.sup.g]
    2         15.47       58.98 [+ or -] [0.55.sup.cd]
              29.15       58.39 [+ or -] [0.94.sup.de]
              41.00       55.03 [+ or -] [0.35.sup.f]
    4         15.47       60.02 [+ or -] [0.87.sup.cd]
              29.15       62.54 [+ or -] [0.43.sup.b]
              41.00       56.79 [+ or -] [0.35.sup.ef]
    8         15.47       60.51 [+ or -] [0.54.sup.c]
              29.15       63.60 [+ or -] [0.76.sup.ab]
              41.00       56.87 [+ or -] [0.72.sup.ef]
   16         15.47       64.95 [+ or -] [0.81.sup.a]
              29.15       63.98 [+ or -] [0.35.sup.ab]
              41.00       59.42 [+ or -] [0.72.sup.cd]

     Treatment

Salinity   Carbohydrate
  (%)          (%)               AE (%)

    1         15.47       84.92 [+ or -] 0.99
              29.15       84.42 [+ or -] 0.90
              41.00       85.21 [+ or -] 1.30
    2         15.47       85.41 [+ or -] 0.98
              29.15       96.13 [+ or -] 0.90
              41.00       84.43 [+ or -] 1.11
    4         15.47       85.52 [+ or -] 1.01
              29.15       86.29 [+ or -] 1.04
              41.00       85.18 [+ or -] 1.22
    8         15.47       86.13 [+ or -] 0.88
              29.15       86.12 [+ or -] 0.86
              41.00       85.44 [+ or -] 1.14
   16         15.47       85.51 [+ or -] 1.01
              29.15       86.50 [+ or -] 1.01
              41.00       85.53 [+ or -] 0.94

Means in the same column sharing a common superscript letter were
not significantly different (P > 0.05) as determined by Tukey's
test. IW, initial weight; FW, finial weight; FC, food consumption;
F[E.sub.f], food efficiency; AE, absorption efficiency; values are
means of three groups of L. vannamei juveniles, with 4 shrimp per
group (n = 4).

TABLE 3.
The relationship between specific growth rate, food consumption,
food efficiency or the percentage of consumed energy allocated to
growth, respiration or excretion (C%), salinity, and dietary
carbohydrate.

                                                              [R.sup.2]

SGR = 0.391 + 0.133S + 0.258CBH - 0.004516CB[H.sup.2]
  - 0.002142S * CBH                                             0.836
FC = 0.986 + 0.141S + 0.323CBH - 0.005733CB[H.sup.2]
  - 0.0021S * CBH                                               0.867
F[E.sub.f] = 35.017 + 1229S + 1.492CBH - 0.02498CB[H.sup.2]
  - 0.02237S * CBH                                              0.583
G/C = 0.01177 + 0.634S + 0.921CBH - 0.01593CB[H.sup.2]
  - 0.009113S * CBH                                             0.745
R/C = 81.113 - 0.575S - 0.597CBH + 0.01285CB[H.sup.2]
  + 0.008489S * CBH                                             0.816
U/C = 10.831 - 0.06321S - 0.162CBH + 0.0009724S * CBH           0.986

S, salinity; CBH, carbohydrate; SGR, specific growth rate; FC, food
consumption; F[E.sub.f], food efficiency; G/C, the percentages of
consumed energy allocated to growth; R/C, the percentages of consumed
energy allocated to respiration; U/C, the percentages of consumed
energy allocated to excretion (%).

TABLE 4.
The relationship between specific growth rate or the percentage of
consumed energy invested in growth (%C) and dietary carbohydrate.

   Salinity
[per thousand]                                           [R.sup.2]

      1          SGR = -50.039CB[H.sup.2] + 29.896CBH      0.969
                   - 0.517
      2          SGR = -37.783CB[H.sup.2] + 20.845CBH      0.971
                   + 1.2562
      4          SGR = -60.59CB[H.sup.2] + 32.535CBH       0.984
                   + 0.4569
      8          SGR = -56.578CB[H.sup.2] + 29.709CBH      0.975
                   + 0.9711
     16          SGR = -20895CB[H.sup.2] + 9.316CBH        0.932
                   + 3.9162
      1          G/C = -328.32CB[H.sup.2] + 192.76CBH      0.999
                   - 14.716
      2          G/C = -159.91CB[H.sup.2] + 85.539CBH      0.988
                   + 3.1997
      4          G/C = -116.72CB[H.sup.2] + 61.854CBH      0.985
                   - 7.6482
      8          G/C = -133.54CB[H.sup.2] + 70.511CBH      0.985
                   - 7.374
     16          G/C = -58.178CB[H.sup.2] + 21.439CBH      0.984
                   + 16.214

   Salinity                                              [Max.sub.CBH]
[per thousand]                                                (%)

      1          SGR = -50.039CB[H.sup.2] + 29.896CBH        29.87
                   - 0.517
      2          SGR = -37.783CB[H.sup.2] + 20.845CBH        27.59
                   + 1.2562
      4          SGR = -60.59CB[H.sup.2] + 32.535CBH         26.85
                   + 0.4569
      8          SGR = -56.578CB[H.sup.2] + 29.709CBH        26.25
                   + 0.9711
     16          SGR = -20895CB[H.sup.2] + 9.316CBH          22.29
                   + 3.9162
      1          G/C = -328.32CB[H.sup.2] + 192.76CBH        29.36
                   - 14.716
      2          G/C = -159.91CB[H.sup.2] + 85.539CBH        26.75
                   + 3.1997
      4          G/C = -116.72CB[H.sup.2] + 61.854CBH        26.50
                   - 7.6482
      8          G/C = -133.54CB[H.sup.2] + 70.511CBH        26.40
                   - 7.374
     16          G/C = -58.178CB[H.sup.2] + 21.439CBH        18.43
                   + 16.214

CBH, carbohydrate; SGR, specific growth rate; G/C, the percentage of
consumed energy invested in growth (C%); [Max.sub.CBH], the optimal
carbohydrate corresponding to maximum specific growth rate or the
percentage of growth (C%).

TABLE 5.
The effects of salinity and dietary carbohydrate levels
on energy budget of L. vannamei juveniles.

     Treatment

Salinity   Carbohydrate      C (1) (kJx[g.sup.-1]
  (%)          (%)               x [d.sup.-1])

    1         15.47       1.33 [+ or -] [0.08.sup.d]
              29.15       1.72 [+ or -] [0.04.sup.b]
              41.00       1.34 [+ or -] [0.09.sup.d]
    2         15.47       1.38 [+ or -] [0.08.sup.d]
              29.15       1.77 [+ or -] [0.05.sup.b]
              41.00       1.35 [+ or -] [0.02.sup.d]
    4         15.47       1.66 [+ or -] [0.05.sup.bc]
              29.15       2.21 [+ or -] [0.09.sup.a]
              41.00       1.40 [+ or -] [0.05.sup.d]
    8         15.47       1.80 [+ or -] [0.11.sup.b]
              29.15       2.22 [+ or -] [0.10.sup.a]
              41.00       1.43 [+ or -] [0.08.sup.cd]
   16         15.47       2.23 [+ or -] [0.11.sup.a]
              29.15       2.23 [+ or -] [0.09.sup.a]
              41.00       1.81 [+ or -] [0.11.sup.b]

     Treatment

Salinity   Carbohydrate
  (%)          (%)                   G (3)

    1         15.47        7.25 [+ or -] [0.08.sup.k]
              29.15       13.58 [+ or -] [0.08.sup.g]
              41.00        9.13 [+ or -] [0.06.sup.j]
    2         15.47       12.61 [+ or -] [0.09.sup.h]
              29.15       14.55 [+ or -] [0.26.sup.f]
              41.00       11.39 [+ or -] [0.13.sup.i]
    4         15.47       14.42 [+ or -] [0.23.sup.f]
              29.15       15.76 [+ or -] [0.12.sup.d]
              41.00       13.39 [+ or -] [0.04.sup.g]
    8         15.47       15.09 [+ or -] [0.13.sup.e]
              29.15       16.58 [+ or -] [0.20.sup.c]
              41.00       13.83 [+ or -] [0.17.sup.g]
   16         15.47       18.14 [+ or -] [0.26.sup.a]
              29.15       17.52 [+ or -] [0.09.sup.b]
              41.00       15.22 [+ or -] [0.21.sup.c]

     Treatment

Salinity   Carbohydrate
  (%)          (%)                    R (3)

    1         15.47       77.79 [+ or -] [0.27.sup.b]
              29.15       74.05 [+ or -] [0.33.sup.de]
              41.00       80.24 [+ or -] [0.29.sup.a]
    2         15.47       73.01 [+ or -] [0.36.sup.ef]
              29.15       73.62 [+ or -] [0.35.sup.def]
              41.00       77.62 [+ or -] [0.51.sup.b]
    4         15.47       71.40 [+ or -] [0.41.sup.h]
              29.15       72.62 [+ or -] [0.41.sup.fg]
              41.00       76.10 [+ or -] [0.39.sup.c]
    8         15.47       70.94 [+ or -] [0.41.sup.h]
              29.15       71.76 [+ or -] [0.33.sup.gh]
              41.00       75.79 [+ or -] [0.20.sup.c]
   16         15.47       67.90 [+ or -] [0.20.sup.i]
              29.15       71.01 [+ or -] [0.32.sup.h]
              41.00       74.48 [+ or -] [0.40.sup.d]

     Treatment

Salinity   Carbohydrate
  (%)          (%)                   U (3)

    1         15.47       8.73 [+ or -] [0.01.sup.a]
              29.15       5.87 [+ or -] [0.02.sup.e]
              41.00       4.40 [+ or -] [0.03.sup.h]
    2         15.47       8.22 [+ or -] [0.02.sup.b]
              29.15       5.84 [+ or -] [0.03.sup.e]
              41.00       4.30 [+ or -] [0.04.sup.i]
    4         15.47       7.98 [+ or -] [0.03.sup.c]
              29.15       5.65 [+ or -] [0.04.sup.f]
              41.00       4.07 [+ or -] [0.03.sup.j]
    8         15.47       7.96 [+ or -] [0.04.sup.c]
              29.15       5.61 [+ or -] [0.02.sup.fg]
              41.00       4.04 [+ or -] [0.02.sup.j]
   16         15.47       7.65 [+ or -] [0.02.sup.d]
              29.15       5.55 [+ or -] [0.01.sup.g]
              41.00       3.88 [+ or -] [0.03.sup.k]

     Treatment

Salinity   Carbohydrate
  (%)          (%)              F (3)

    1         15.47       5.53 [+ or -] 0.36
              29.15       5.79 [+ or -] 0.38
              41.00       5.52 [+ or -] 0.31
    2         15.47       5.45 [+ or -] 0.37
              29.15       5.28 [+ or -] 0.34
              41.00       5.99 [+ or -] 0.43
    4         15.47       5.48 [+ or -] 0.38
              29.15       5.26 [+ or -] 0.40
              41.00       5.74 [+ or -] 0.44
    8         15.47       5.31 [+ or -] 0.33
              29.15       5.34 [+ or -] 0.43
              41.00       5.63 [+ or -] 0.27
   16         15.47       5.60 [+ or -] 0.39
              29.15       5.21 [+ or -] 0.40
              41.00       5.70 [+ or -] 0.44

     Treatment

Salinity   Carbohydrate
  (%)          (%)              E (3)

    1         15.47       0.70 [+ or -] 0.02
              29.15       0.71 [+ or -] 0.03
              41.00       0.71 [+ or -] 0.01
    2         15.47       0.71 [+ or -] 0.02
              29.15       0.70 [+ or -] 0.02
              41.00       0.70 [+ or -] 0.01
    4         15.47       0.71 [+ or -] 0.02
              29.15       0.72 [+ or -] 0.02
              41.00       0.69 [+ or -] 0.00
    8         15.47       0.73 [+ or -] 0.01
              29.15       0.71 [+ or -] 0.02
              41.00       0.70 [+ or -] 0.01
   16         15.47       0.69 [+ or -] 0.01
              29.15       0.72 [+ or -] 0.01
              41.00       0.70 [+ or -] 0.02

Means in the wine column sharing a common superscript letter were
not significantly different (P > 0.05) as determined by Tukey's
test.

(1) C, the consumed energy; values are means of three groups of L.
vannamei juveniles, with 4 shrimp per group (n = 4).

(2) The energy values expressed as the percentages of consumed
energy.

(3) G, growth; R, respiration; U, excretion; F, feces; E, exuviae;
values are means of three groups of L. vannamei juveniles, with 4
shrimp per group (n = 4).

Figure 1. The effects of salinity and dietary carbohydrates
(CBH) on specific growth rate (SGR) of L. vannamei juveniles;
values are means of three groups of L. vannamei juveniles,
with 4 shrimp per group (n = 4); means with different letters
are significantly different (P < 0.05), and bars indicate
standard errors of the means.

                                  SGR (%)

Salinity           15.47% CBH   29.15% CBH   41.00% CBH

1[per thousand]         f           c            e
2[per thousand]         de          bc           de
4[per thousand]         bc          a            d
8[per thousand]         b           a            d
16[per thousand]        a           a            b

Note: Table made from bar graph.

ACKNOWLEDGMENTS

This study was funded by the Chinese National Agricultural Development Project (Grant no. K2002-15) and the Science Research Council of Shandong Province, China (Grant no. 041656).

LITERATURE CITED

Alava, V. R. & F. P. Pascual. 1987. Carbohydrate requirements of P. monodon (Fabricius) juveniles. Aquaculture 61:211-217.

Ali, S. A. 1982. Effect of carbohydrate (starch) level in purified diets on the growth of P. indicus, Indian J. Fish. 29:201-208.

Anger, K., E. Spivak & T. Luppi. 1998. Effects of reduced salinities on development and bioenergetics of early larval shore crab Carcinus intents. J. Exp. Mar. Biol. Ecol. 220:287-304.

Bindu, R. P. & A. D. Diwan. 2002. Effects of acute salinity stress on oxygen consumption and ammonia excretion rotes of the marine shrimp Metapenaeus monoceros. J. Crust. Biol. 22(1):45-52.

Bray. W. A., A. L. Lawrence & J, R. Leung-Trujillo, 1994. The effect of salinity on growth and survival of Penaeus vannamei, with observations on the interaction of IHHN virus and salinity. Aquaculture 122: 133-146.

Castille, F. L. J. & A. L. Lawrence. 1981. The effect of salinity on the osmotic, sodium and chloride concentrations in the hemolymph of euryhaline shrimp of the genus Penaeus. Comp. Biochem. Physiol. A 68(1):75-80.

Dall. W. 1981. Osmoregulatory ability and juvenile habitat preference in some penaeid prawns. J Exp. Mar. Biol. Ecol. 27:213-250.

Dokken. Q. R. 1987. Effects of varying of dietary macronutrient and energy ratios on growth and survival of penaeus vannamei and penaeus setiferus. Dissertation Abstracts International Part B: Sci. Eng. 48(06): 1559.

Dong, S. L. 2003. Strategy and choice on the sustainable development of aquaculture in drought and inland saline-alkaline land. The future of global aquaculture-reviews In: 2002 World Fisheries Congress, pp. 21-25.

Elliott, J. M. 1976. Energy loses in the waste products of brown trout (Salmon trout L.). J. Anita. Ecol. 45:561-580.

Galli, L. & S. Stern. 1998. Histological changes in cultured Penaeus vannamei induced by low salinity, In: W.C. Valenti, S. Zimmermann, C. R. Poli, A.T. Bassanesi Poli, F.R. Moraes, G. Volpato & M. R. Camara, Aquaculture Brazil '98. Sustainable Development, Recife-PE, Brazil. pp. 2-6.

Guerin, J. L. & W. B. Stickle. 1992. Effect of salinity gradients on the tolerance and bioenergetics of juvenile blue crabs (Callinectes sapidus) from waters of different environmental salinities. Mar. Biol. 114:391-396.

Guerin, J. L. & W. B. Stickle. 1995. Effects of cadmium on survival, osmoregulatory ability and bioenergetics of juvenile blue crabs Callinectes sapidus at different salinities. Mar. Environ. Res. 40(3):227-246.

Hu, A. S. 1958. Glucose metabolism in the crab, Hemigrapsus mudus. Archs. Biochem. Biophys. 75:387-395.

Huang, H. J. 1983. Factors affecting the successful culture of Penaeus stylirostris and Penaeus vannamei at an estuarine power plant site: temperature, salinity, inherent growth variability, damselfly nymph predation, population density and distribution and polyculture. PhD. Dissertation, Texas A&M University. 221 pp.

Panikkar, N. K. 1968. Osmotic behavior of shrimps and prawns in relation to their biology and culture. FAO Fish. Rep. 57:527-538.

Rosas, C., G. Cuzon, G. Gaxiola, L. Arena, P. Lemaire, C. Soyez & A. Van Wormhoudt. 2000. Influence of dietary carbohydrate on the metabolism of juvenile Litopenaeus stylirostris. J. Exp. Mar. Biol. Ecol. 249: 181-198.

Rosas, C., N. Lopez, P. Mercado & E. Martinez. 2001a. Effect of salinity acclimation on oxygen consumption of juveniles of the white shrimp Litopenaeus vannamei. J. Crust. Biol. 21(4):912-922.

Rosas, C., G. Cuzon, G. Taboada, C. Pascual, G. Gaxiola & A. Van Wormhoudt. 2001b. Effect of dietary protein and energy levels on growth, oxygen consumption, haemolymph and digestive gland carbohydrates, nitrogen excretion and osmotic pressure of Litopenaeus vannamei (Boone) and L. setiferus (Linne) juveniles (Crustacea, Decapoda; Penaeidae). Aquacul. Res. 32(7):531-547.

Saoud, I. S., D. A. Davis & D. B. Rouse. 2003. Suitability studies of inland well waters for Litopenaeus vannamei culture. Aquaculture 217:373-383.

Staples, D. J. & D. S. Heales. 1991. Temperature and salinity optima for growth and survival of juvenile banana prawn Penaeus merguiensis. J. Exp. Mar. Biol. Ecol. 154:251-274.

Wang, J. Q., H. L. Lui, H. Y. Po & L. N. Fan. 1997. Influence of salinity on food consumption, growth and energy conversion efficiency of common carp (Cyprinus carpio) fingerlings. Aquaculture 148:115-124.

Zhang, S. & S. L. Dong. 2002. The effects of food and salinity on energy budget of juvenile shrimp of Penaeus chinensis juveniles. J. Dalian Fish. University 17(3):227-233.

XINGQIANG WANG, SHEN MA, * SHUANGLIN DONG AND MEI CAO Mariculture Research Laboratory, Fisheries College, Ocean University of China, Qingdao, 266003, People's Republic of China

* Corresponding author. E-mail: [e-mail]