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The interaction of salinity and Na/K ratio in seawater on growth, nutrient retention and food conversion of juvenile Litopenaeus Vannamei.

ABSTRACT The effects of salinity, Na/K ratio and their interaction on growth, molting, nutrient retention and food conversion of Litopenaeus vannamei were investigated. The test shrimp were reared in artificial seawater and fed fresh polychaete worms, Neanthes japonica (Izuka) for 30 days. Two salinities (30 and 15 ppt) and 5 Na/K ratios (25.6, 34.1, 47.3, 102.1 and 153.3, retool/retool) were set, and each treatment had four replicates. During the feeding trial, the molting frequency (MF) was affected by neither salinity nor interaction effects, but Na/K ratio had an effect (P < 0.05). And there was a tendency that MF rose with the increment of Na/K ratio at both salinities. Final body weight, weight gain (WG) and specific growth rate (SGR) were significantly influenced by salinity, Na/K ratio and interaction effects (P < 0.05), whose mean values at salinity 15 ppt were significantly higher than those at 30 ppt. At 30 ppt, WGs and SGRs of shrimp exposed to Na/K ratio 34.1 and 47.3 were respectively more than 26% and 15% higher than of those exposed to the other ratios (P < 0.05), but no significant differences in growth were found among treatments at 15 ppt (P > 0.05). Na/K ratio and interaction effects significantly affected the nutrient retention (PR and ER), food conversion (FCE) and protein utility (PER) of the shrimp (P < 0.05), whereas salinity showed little impact. At 30 ppt, the PR and ER of shrimp exposed to Na/K ratio 153.3 were more than 30% lower than of those exposed to the other 4 ratios (P < 0.05); the FCEs of shrimp exposed to Na/K ratio 34.1 and 47.3 were more than 20% higher than of those exposed to Na/K ratio 25.6 and 102.1 (P < 0.05), and the FCE of shrimp exposed to Na/K ratio 153.3 was even lower (P < 0.05). At 15 ppt, no significant differences in FCE among treatments were found (P > 0.05). PER showed the similar tendency as FCE at both salinities. It was indicated that the shrimp were more adaptable to abnormal Na/K ratios at low salinity than at higher salinities, and good growth could always be obtained within a Na/K range of 34.1-47.3 (mmol/mmol) regardless of salinity.

KEY WORDS: salinity, Na/K ratio, interaction, Litopenaeus vannamei, growth

INTRODUCTION

Inland production of shrimp using water from saline aquifers is providing an alternative to traditional coastal aquaculture and a diversification of agriculture, and it is currently undertaken in the United States, Ecuador, Brazil, China and several other countries (Boyd 2002, McGraw et al. 2002). Until the year 2003, inland shrimp farming was present in 25 of the 31 Chinese provinces and autonomous regions, and the annual production of L. vannamei cultured in inland has amounted to 296,300 tons in China (Liu et al. 2004).

Although the shrimp farming technology in seawater has reached a high level, it could not be introduced to inland saline water culture directly. Comparative to seawater, the ion profile has changed a lot, and the rule of constancy of composition of seawater does not apply to inland saline water. Furthermore, the ionic composition and salinity of ground water among places can vary markedly; the natural saline water resources in many inland places could not be used in shrimp culture directly (Boyd 2002, Davis et al. 2002, Saoud et al. 2003). For example, In the saline-alkaline area of Yellow River Delta in China, the saline ground waters are chloride type, salinity varies between 5-15 ppt and most of their chemical compositions are similar to that of oceanic seawater of the same salinity except potassium, which is 90% to 95% less than similar salinity oceanic seawater, and shrimp could not survive (Wang et al. 2001, Li et al. 2002).

Current data suggests that salinity and proper ionic composition of saline water are the two necessities for culture suitability evaluations. Numerous reports focus on effects of salinity on shrimp culture (Dalla Via 1986a, 1986b, Huang 1983, Bartlett et al. 1990, Bray et al. 1994, Vinod et al. 1996, Chen et al. 1996, Ponce-Palafox et al. 1997, Rosas et al. 2001). More studies have begun concerning the ionic imbalance of saline water, especially on supplementing potassium into potassium deficient saline water for shrimp and marine fish culture (Liu 2001, Fielder et al. 2001, Allan & Fielder 2002, McGraw & Scarpa 2003). In addition, Forsberg et al. (1996) reported that the survival of red drum Sciaenops ocellatus was significantly corrected with the Na/K and K/Cl ratios of the saline ground water. Zhu et al. (2004) did special experimental work on the effects of Na/K ratio in seawater on growth and energy budget of juvenile L. vannamei, and they found that Na/K ratio had significant effects on the survival, molting, growth and energy budget of the shrimp at salinity 30 ppt. However, salinity fluctuation and ionic imbalance often occur simultaneously in saline ground water, and they might interact on the aquatic animals. The aim of this research is to evaluate the interaction of salinity and Na/K ratio in seawater on the growth of L. vannamei under laboratory conditions, thus to further the knowledge on shrimp farming with inland saline ground water.

MATERIALS AND METHODS

Source and Acclimation of Juvenile Litopenaeus vannamei

The experiment was carried out between June 14 and July 13, 2003. Juvenile L. vannamei were obtained from the Jiaozhou Shrimp Farm in Qingdao, China. When the shrimp were transported to the laboratory, one half was stored in two continuously aerated 600-1 fiberglass tanks with natural seawater (29-31 ppt), and the other half was stored with diluted seawater (15 ppt) to undergo a 10-day acclimation to the indoor laboratory conditions, during which they were fed ad libitum twice a day (8:00 and 18:00) with commercial shrimp ration pellets (composition: 41.58% crude protein, 8.36% crude lipid and 8.74% moisture; energy content: 19.37 kJ/g dry matter).

Experimental Design and Artificial Seawater Preparation

To eliminate the interference of imbalance from other ions, the experimental water was prepared by adding instant artificial seasalts into fully aerated tap water. The instant artificial seasalts were specially designed and produced by General Sea Salt Factory, Ocean University of China, in which the sodium and potassium ingredients were precisely compounded so as to keep their total concentration constant, whereas the Na/K ratios varied. The salinity of the newly prepared artificial seawaters was 30 ppt and 15 ppt and pH 8.2. At each salinity level, the total concentration of monovalent cations and other ions were kept approximately constant. Based on the former experiment result (Zhu et al. 2004), 5 Na/K ratios were set: 25.6, 34.1, 47.3, 102.1 and 153.3 (mmol/mmol), in which 47.3 was identical with the Na/K ratio of oceanic seawater, and it was set as control. The concentrations of Na+ and K+ were determined with an inductively coupled plasma-atomic emission spectrophotometer (ICP-OES; VISTA-MPX, VARIAN). The details are given in Table 1.

After the 10-day acclimation and 24 h starvation, shrimp of similar size were selected and weighted individually. To remove excess moisture, shrimp were blotted dry with paper towel and weighted to the nearest 0.001 g using an electronic balance. Two-hundred shrimp that weighted 1.554 [+ or -] 0.004 g (mean [+ or -] SE) were selected, and 160 were randomly assigned to 40 glass aquaria (45 x 25 x 30 cm, 4 individuals/aquarium) to take the 30-day feeding trial. The aquaria were filled with 30 L artificial seawater of different salinities (15 ppt and 30 ppt) and Na/K ratios (25.6, 34.1, 47.3, 102.1 and 153.3). Therefore, 10 treatments, 4 replicates per treatment were conducted. The aquaria were randomly located. To prevent the shrimp from jumping out, every aquarium was

covered with a mesh cover. The ambient temperature was controlled with an air-conditioner. Aeration was provided continuously and two-thirds of the water volume was exchanged every second day to ensure high water quality. During the experiment, dissolved oxygen was maintained above 6.0 mg/L, pH 8.1 [+ or -] 0.2, water temperature at 25[degrees]C [+ or -] 0.5[degrees]C, and a simulated natural photoperiod (14 light: 10 dark) was used. The remaining 40 shrimp were dried in an oven at 65[degrees]C to constant weight, homogenized and stored at -20[degrees]C to estimate the body composition and energy content of the initial shrimp. During the feeding trial, the shrimp were fed fresh polychaete worms, Neanthes japonica (Izuka), which had been considered to be the best natural diet in prompting shrimp growth and was widely used in shrimp farming in China (Bi et al. 1995, Zhou & Xie 1995). The shrimp were fed at satiation level twice a day (6:00 and 16:00).

Samples Collection and Analysis

During the course of the experiment, the daily food (polychaete worms) supplied was blotted dry with paper towel and precisely weighed and recorded. The uneaten food and feces were collected by siphon within 3 h after each meal. Exuviae (molted exoskeletons) were collected and recorded at all times. The collected uneaten food, feces and exuviae were dried at 65[degrees]C and kept for further analysis. At the end of the experiment, all the test shrimp were starved for 24 h and then collected and dried at 65[degrees]C to constant weight. The shrimp from the same aquarium were pooled as a sample.

Nitrogen content was measured using Kjeltec Auto System 2200 (Foss, Sweden), and crude protein content was calculated from nitrogen content by multiplying 6.25 (AOAC 1984). Crude lipid was determined by the Soxthlet method (AOAC 1984). The energy content of dried samples was determined by Parr 1281 Oxygen Bomb Calorimeter (PARR Instrument Company, USA). Analyses of each sample were conducted in triplicates. The body composition of polychaete worm was analyzed in the same way as the shrimp samples and found to be: 83.6% moisture, 77.8% (dry matter) crude protein and 7.2% (dry matter) crude lipid; energy content was 21.31 kJ/g dry matter.

Calculation and Data Analysis

Weight gain (WG), specific growth rate (SGR), molting frequency (MF), feeding rate (FR), food conversion efficiency (FCE) and protein efficiency ratio (PER) were calculated as follows:

WG (%) = 100([W.sub.2]-[W.sub.1])/[W.sub.1] SGR (% x [day.sup.-1]) = 100(1n[W.sub.2] - 1n [W.sub.1])/T MF (% x [day.sup.-1]) = 100[N.sub.m]/([N.sub.s] x T) FR (% body weight x [day.sup.-1]) = 100C/[T ([W.sub.2] + [W.sub.1])/2] FCE (%) = 100([W.sub.2] - [W.sub.1])/C PER = ([W.sub.2] - [W.sub.1])/(C x Protein content)

Apparent energy or protein retention levels (ER and PR, respectively) were calculated as: [([W.sub.2] x (final energy or protein content/100)) - ([W.sub.1] x (initial energy or protein content/100))]/ C x (% energy or protein in food/100) (Hardy 1989).

Where [W.sub.2] and [W.sub.1] are the final and initial wet body weight of the shrimp, [N.sub.m] is the number of molts, [N.sub.s] is the number of shrimp, T is the duration of the experiment, and C is the total food consumed.

Statistics were performed with SPSS 10.0 statistical software (SPSS Inc., 1999). The assumption of homogeneity of variances was tested for all data, which were [sin.sup.-1]-transformed if necessary. Two-way analysis of variance (ANOVA) was used to test for the interaction of salinity and Na/K ratio in seawater on all data. Significant ANOVAs were followed by a Student-Neumann-Keuls multiple comparison test to locate differences between groups. Significance was accepted when P < 0.05.

RESULTS

Survival and Molting

The survival and molting data of the test shrimp are presented in Table 2. During the 30-day experiment, there were 2 shrimp that died within one aquarium at salinity 30 ppt and Na/K ratio 25.6, and another 2 shrimp died while exposed to Na/K ratio 25.6 and 102.1 at salinity 15 ppt. However, no significant differences in survival among treatments were found (P > 0.05).

No significant interaction effects in molting frequencies (MF) were found, whereas the Na/K ratio had an effect (P < 0.05). At salinity 30 ppt, MFs for shrimp exposed to Na/K ratio 102.1 and 153.3 are much higher than for those exposed to lower Na/K ratios, even significantly higher than for the control (Na/K = 47.3) (P < 0.05). No significant differences in MFs were found among treatments at salinity 15 ppt, but it could be seen that MF increases, whereas Na/K ratio becomes higher.

Growth

At the beginning of the feeding trial, the body weights of the test shrimp under each treatment were similar (Table 2). At the end of the experiment, the final body weight of the shrimp were significantly influenced by salinity, Na/K ratio and interaction effects (P < 0.05). At salinity 30 ppt, the mean final body weight for shrimp at Na/K ratio 153.3 was significantly lower than for those at the other four Na/K ratios (P < 0.05), yet no significant differences in final body weight were found between shrimp exposed to the latter four ratios (P > 0.05). Shrimp at salinity 15 ppt had significantly higher mean final body weight than at salinity 30 ppt (P < 0.05). Na/K ratio showed no effects on shrimp final body weight at 15 ppt (P > 0.05), although it did at 30 ppt (P < 0.05). The mean final body weight for shrimp exposed to Na/K ratio 34.1 and 47.3 was higher than for those exposed to the other three ratios at both salinities.

Weight gain (WG) and specific growth rate (SGR) both were significantly affected by salinity, Na/K ratio and interaction effects (P < 0.05). At salinity 30 ppt, WGs of the shrimp exposed to Na/K ratio 34.1 and 47.3 were significantly higher than those exposed to Na/K ratio 25.6 and 102.1 (P < 0.05), and WG of the shrimp at Na/K ratio 153.3 was even lower (P < 0.05). However, no significant differences were in WG among Na/K ratios at salinity 15 ppt (P > 0.05), and the mean WG for shrimp at salinity 15 ppt was significantly higher than for that at salinity 30 ppt (P > 0.05). SGR has the similar tendency as WG.

Food Intake, Nutrient Retention and Food Conversion Efficiency

Data of food intake, nutrient retention and food conversion efficiency are presented in Table 3. No significant interaction effects were observed in feeding rates (FR) (P > 0.05), though salinity and Na/K ratio both showed an effect (P < 0.05). Shrimp at salinity 15 ppt had higher FRs than at salinity 30 ppt (P < 0.05). Although no significant difference in FR was found among Na/K ratios at salinity 15 ppt (P > 0.05), FR for shrimp exposed to Na/K ratio 25.6 showed the highest FR at salinity 30 ppt, which was significantly higher than for those exposed to Na/K ratio 34.1, 47.3 and 153.3 (P < 0.05).

Protein retention (PR) and energy retention (ER) were significantly affected by Na/K ratio and interaction effects (P < 0.05), whereas salinity showed no significant influence (P > 0.05). At salinity 30 ppt, PR of the shrimp at Na/K ratio 153.3 was significantly lower than of those at the other 4 Na/K ratios (P < 0.05), and no significant differences in PR were found between the latter 4 treatments (P > 0.05). At salinity 15 ppt, significant differences in PR were only found between shrimp exposed to Na/K ratio 25.6 and 47.3 (P < 0.05). ER had the similar tendency as PR (Table 3).

Salinity showed no significant effects on food conversion efficiency (FCE) and protein utilization (PER) (P > 0.05). However, at salinity 30 ppt, FCE was significantly affected by Na/K ratios. The FCEs for shrimp exposed to Na/K ratio 34.1 and 47.3 were significantly higher than for those exposed to Na/K ratio 25.6 and 102.1 (P < 0.05), and the FCE for shrimp at Na/K ratio 153.3 was even lower (P < 0.05). However, no significant differences in shrimp FCE were found among different Na/K ratios at salinity 15 ppt (P > 0.05). PER showed the similar tendency as FCE.

Interaction of Salinity and Na/K Ratio on Specific Growth Rate and Food Conversion Efficiency

As presented in Table 2 and Figure 1, significant effects of salinity, Na/K ratio and interaction were found in SGR (P < 0.05). At both salinities SGR changed, whereas the Na/K ratio in seawater increased. However, the SGRs at salinity 30 ppt changed sharply, whereas those at salinity 15 ppt changed gently. At salinity 30 ppt, the SGR was low at Na/K ratio 25.6, but it mounted up rapidly at Na/K ratio 34.1 (P < 0.05) and then declined a little at Na/K ratio 47.3 (P > 0.05). Afterwards it made an acute drop at Na/K ratio 102.1 and 153.3 (P < 0.05), respectively. Although no significant differences in SGR were found at salinity 15 ppt, it still could be observed that SGR rose gently, whereas Na/K ratio increased from 25.6-47.3 and then declined when Na/K ratio continued to increase. At salinity 30 ppt, the maximum value of SGR occurred at Na/K ratio 34.1, whereas at salinity 15 ppt, the maximum value emerged when Na/K ratio was 47.3, though the two values were almost equal.

[FIGURE 1 OMITTED]

Interaction effects on FCE are pictured in Figure 2. Similar to SGR, changes of FCE at salinity 30 ppt were much more acute than those at salinity 15 ppt. At salinity 30 ppt, shrimp got the highest FCE when Na/K ratio was 34.1, and at salinity 15 ppt they got it, whereas Na/K ratio was 47.3. However, under Na/K ratio 34.1 and 47.3, the FCEs at salinity 30 ppt were much higher than those at salinity 15 ppt. Otherwise, the FCEs at salinity 30 ppt were lower than those at salinity 15 ppt under the other Na/K ratios (25.6, 102.1 and 153.3). As a result, no significant differences were found between the mean values of FCEs at the two test salinities (P > 0.05).

[FIGURE 2 OMITTED]

DISCUSSION

It is known that L. vannamei can tolerate a wide salinity range from brackish water of 1-2 ppt to hypersaline water of 50 ppt (Stern et al. 1990, McGraw et al. 2002). Boyd (1989) considered salinity of 15-25 ppt to be ideal for L. vannamei culture. But, in view of inconsistencies in published information regarding salinity effects on shrimp survival and growth, the optimum salinity for L. vannamei is still not conclusive. Bray et al. (1994) showed that 5 and 15 ppt treatments produced significantly greater final weights than other levels (25, 35 and 49 ppt) tested. However, Ponce-Palafox et al. (1997) concluded that the growth of L. vannamei was not reduced at the salinity range of 25-45 ppt, and there were significant interaction effects of salinity and temperature on the growth and survival rates of the shrimp. Laramore et al. (2001) found that the effects of salinity on growth varied with size/age. In this research, it is clear that interaction of salinity and Na/K ratio in seawater bas significant influence on the growth of L. vannamei (Table 2). The mean final body weights, weight gains and specific growth rates of the shrimp at salinity 15 ppt were significantly higher than those at salinity 30 ppt (P < 0.05), but it should be noted that good growth had always been obtained under Na/K ratio 34.1 and 47.3 at both salinities. At salinity 15 ppt, no significant effects were found in growth between treatments of different Na/K ratios (P > 0.05), whereas the growth of shrimp under Na/K ratio 34.1 and 47.3 were much better than under the other ratios at salinity 30 ppt (P < 0.05).

Customarily, salinity is one of the most compelling factors to most marine animals, but the ionic composition of saline water seems to be more important than salinity with regards to its effect on shrimp survival and growth (Davis et al. 2002, Saoud et al. 2003). Cawthorne et al. (1983) demonstrated that single salt solutions (NaCl) were not suitable for shrimp culture at any salinity. Additionally, Atwood et al. (2003) found that L. vannamei larvae could survive well in the solution containing 1 g/L sea salt, and they could survive fairly well after adding 4 g Ca[Cl.sub.2] or 2 g Ca[Cl.sub.2] and 2 g NaCl and the salinity reached 5 g/L, but no survival would have resulted if 4 g NaCl had been added. They speculated that sodium ratio to some other ion in the solution may be too high. Zhu et al. (2004) demonstrated that high Na/K ratio in seawater resulted poor survival of L. vannamei. In this experiment, the effects of salinity on growth, nutrient retention and food conversion were much less than that of Na/K ratio and even interaction (Table 2, 3).

The importance of Na/K ratio might because of the indispensable role of potassium in crustacean osmolality maintenance and [Na.sup.+]/[K.sup.+] ATPase activity (Winkler 1986, Vargas-Albores & Ochoa 1992). It has been demonstrated in some penaeids that the sodium and/or potassium hemolymph concentrations were modified according to the concentration of these ions in the external medium (Castille & Lawrence 1981, Dall & Smith 1981). Potassium is important in the activation of [Na.sup.+]/[K.sup.+] ATPase (Mantel & Farmer 1983), which is involved in ion transport and osmoregulation. In the [K.sup.+]-free saline, oxygen consumption of the excised gills of the shore crab Carcinus mediterraneus was reduced by almost 40% (Lucu & Pavicic, 1995), it suggested that 30% to 40% of the energy liberated by gill respiration is used by the branchial [Na.sup.+]/[K.sup.+] ATPase enzyme complex, maintaining [Na.sup.+] and [K.sup.+] concentration gradients between the extracellular and intracellular compartments. The central role of the [Na.sup.+]/[K.sup.+] ATPase in the crustacean gill epithelium and the sodium gradient that is used to drive numerous processed has been described (see Lucu 1990). The variation of salinity (ionic intensity) may directly affect the ionic gradients between the extracellular and intracellular compartments of the shrimp, which would inevitably impact the activity of [Na.sup.+]/[K.sup.+] ATPase, thus the interaction between salinity and Na/K ratio occurs.

Because of the limitation of labor and space, low salinity ([less than or equal to] 5 ppt) was not included in this experiment, and only 2 salinity levels (30 and 15 ppt) were tested, which made a flaw to the research. However, the result at 15 ppt might give some inspiration on the comprehension of effects of Na/K ratio at low salinity. Na/K ratios within the experimental range (25.6-153.3, mmol/mmol) showed little impact on the growth of L. vannamei at 15 ppt, which indicated that the shrimp were more adaptable to abnormal Na/K ratios at low salinity than at higher salinities. Additionally, a few recent literature have concerned the ionic challenge on the survival and growth of L. vannamei at low salinities and freshwater. McGraw and Scarpa (2003) demonstrated that necessity of potassium in "freshwater" (1 ppt) at a minimum concentration of 1 ppm for the survival of L. vannamei postlarval. It could be figured out that the 48-h survival of the shrimp did not differ significantly, whereas the Na/K ratio changed between 10 and 490 (mmol/mmol). Such results fairly coincided with the actions of the shrimp at salinity 15 ppt in the present study.

In conclusion, the interaction of salinity and Na/K ratio in seawater had significant effects on growth, feeding, nutrient retention and food conversion (P < 0.05) of L. vannamei. The shrimp were more adaptable to abnormal Na/K ratios at low salinity than at higher salinities, and good growth could always be obtained within a Na/K range of 34.1-47.3 (mmol/mmol) regardless of salinity. However, further research was needed to confirm the proper range of Na/K ratio for the growth of shrimp at low salinities ([less than or equal to] 5 ppt).

ACKNOWLEDGMENTS

The authors thank General Sea Salt Factory of Ocean University of China, for designing and producing the experimental instant seasalts. This work was funded by the project under the Major State Basic Research of China (Grant no. 2002AA648010) and the National 10th Five Year Major Program (Grant no. 2004BA526B0402).

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Zhu, C., S. Dong, F. Wang & G. Huang. 2004. Effects of Na/K ratio in seawater on growth and energy budget of juvenile Litopenaeus vannamei. Aquaculture 234:485-496.

CHANG-BO ZHU, (1,2) SHUANG-LIN DONG (1) * AND FANG WANG (1)]

(1) Mariculture Research Laboratory, Fisheries College, Ocean University of China, Qingdao, 266003, China; (2) Aquaculture and Biotechnology Division, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, 510300, China

* Corresponding author. E-mail: dongsl@mail.ouc.edu.cn
TABLE 1.

Concentrations of [Na.sup.+], [K.sup.+] ([mmlL.sup.-1]) and Na/K
ratios of the experimental artificial seawater.

 25.6 34.1 47.3
Na/K ratio
Salinity (ppt) 30 15 30 15 30 15

[Na.su.+] 393.2 197.6 398.0 199.5 402.0 201.0
[K.sup.+] 15.4 7.7 11.7 5.9 8.5 4.2
[Na.sup.+] + [K.sup.+] 408.6 205.3 409.7 205.4 410.5 205.2

 102.0 153.3
Na/K ratio
Salinity (ppt) 30 15 30 15

[Na.su.+] 408.0 203.3 409.5 204.0
[K.sup.+] 4.0 2.0 2.7 1.3
[Na.sup.+] + [K.sup.+] 412.0 205.3 412.1 205.3

TABLE 2.

Growth, survival and molting of L. vannamei in the artificial seawater
of different salinities and Na/K ratios during 30 days. ([dagger])

 Body wet weight (g)
 Salinity Na/K
 (ppt) ratio Initial Final

 30 25.6 1.566 [+ or -] 0.010 5.289 [+ or -] 0.138 b
 34.1 1.544 [+ or -] 0.006 6.277 [+ or -] 0.071 b
 47.3 1.544 [+ or -] 0.017 6.198 [+ or -] 0.507 b
 102.1 1.566 [+ or -] 0.017 5.274 [+ or -] 0.135 b
 153.3 1.541 [+ or -] 0.009 3.491 [+ or -] 0.180 a*
 15 25.6 1.553 [+ or -] 0.009 5.880 [+ or -] 0.231
 34.1 1.565 [+ or -] 0.015 6.115 [+ or -] 0.268
 47.3 1.558 [+ or -] 0.010 6.345 [+ or -] 0.209
 102.1 1.556 [+ or -] 0.017 5.826 [+ or -] 0.282
 153.3 1.550 [+ or -] 0.008 5.630 [+ or -] 0.123*
Two-way analysis of variance ([double dagger])
 Salinity -- S (<0.001)
 Na/K ratio -- S (<0.001)
 Salinity x
 (Na/K
 ratio) -- S (0.001)

 Salinity Na/K WG SGR
 (ppt) ratio (%) (% x [day.sup.-1])

 30 25.6 237.91 [+ or -] 10.65 b 4.05 [+ or -] 0.11 b
 34.1 306.60 [+ or -] 4.87 c 4.67 [+ or -] 0.04 c
 47.3 300.76 [+ or -] 29.71 c 4.60 [+ or -] 0.25 c
 102.1 236.82 [+ or -] 9.35 b 4.04 [+ or -] 0.09 b
 153.3 126.56 [+ or -] 11.54 a* 2.71 [+ or -] 0.17 a*
 15 25.6 278.46 [+ or -] 13.91 4.43 [+ or -] 0.12
 34.1 291.27 [+ or -] 20.95 4.53 [+ or -] 0.17
 47.3 307.47 [+ or -] 15.45 4.68 [+ or -] 0.13
 102.1 275.15 [+ or -] 21.70 4.39 [+ or -] 0.21
 153.3 263.15 [+ or -] 6.61 * 4.30 [+ or -] 0.06 *
Two-way analysis of variance ([double dagger])
 Salinity S (<0.001) S (<0.001)
 Na/K ratio S (<0.001) S (<0.001)
 Salinity x
 (Na/K
 ratio) S (0.001) S (<0.001)

 Salinity Na/K MF Survival
 (ppt) ratio (% x [day.sup.-1]) (%)

 30 25.6 12.29 [+ or -] 0.31 ab 87.5 [+ or -] 7.2
 34.1 11.88 [+ or -] 1.20 ab 100.0 [+ or -] 0.0
 47.3 11.04 [+ or -] 0.63 a 100.0 [+ or -] 0.0
 102.1 14.38 [+ or -] 0.21 b 100.0 [+ or -] 0.0
 153.3 13.96 [+ or -] 0.40 b 100.0 [+ or -] 0.0
 15 25.6 10.56 [+ or -] 1.53 93.8 [+ or -] 6.3
 34.1 11.18 [+ or -] 0.44 100.0 [+ or -] 0.0
 47.3 12.29 [+ or -] 1.04 100.0 [+ or -] 0.0
 102.1 13.54 [+ or -] 0.79 93.8 [+ or -] 6.3
 153.3 13.33 [+ or -] 0.59 100.0 [+ or -] 0.0
Two-way analysis of variance ([double dagger])
 Salinity NS (0.317) NS (0.999)
 Na/K ratio S (0.005) NS (0.061)
 Salinity x
 (Na/K
 ratio) NS (0.486) NS (0.566)

WG, weight gain; SGR, specific growth rate; MF, molting frequency.

([dagger]) Mean [+ or -] SE of four replicates. Means within a column
and within each salinity level followed by different letters are
significantly different (Student-Neumann-Keuls multiple comparison,
P < 0.05). Means at the same Na/K ratio level were compared between
salinity 30 and 15 ppt, an (*) followed the means indicates
significant difference (P < 0.05).

([double dagger]) Decimal fraction within each bracket denotes the
P value of two-way ANOVA. S, significant (P < 0.05); NS, not
significant (P > 0.05).

TABLE 3.

Feeding, nutrient retention, food conversion and protein utility of
L. vannamei during the 30-day experiment. ([dagger])

 Salinity Na/K
 (ppt) ratio FR (%) PR (%)

 30 25.6 18.68 [+ or -] 0.40 b 32.98 [+ or -] 4.48 b
 34.1 16.35 [+ or -] 0.58 a 36.97 [+ or -] 0.89 b
 47.3 16.53 [+ or -] 0.19 a 36.41 [+ or -] 2.39 b
 102.1 17.66 [+ or -] 0.30 ab 31.92 [+ or -] 0.88 b
 153.3 16.25 [+ or -] 0.73 a 22.46 [+ or -] 1.06 a*
 15 25.6 19.13 [+ or -] 0.56 29.40 [+ or -] 1.16 x
 34.1 17.86 [+ or -] 0.17 33.74 [+ or -] 1.02 xy
 47.3 17.80 [+ or -] 0.21 34.79 [+ or -] 1.06 y
 102.1 18.50 [+ or -] 0.35 31.74 [+ or -] 1.34 xy
 153.3 18.40 [+ or -] 0.33 31.21 [+ or -] 0.69 xy*
Two-way analysis of variance ([double dagger])
 Salinity S (<0.001) NS (0.974)
 Na/K ratio S (0.001) S (<0.001)
 Salinity x NS (0.335) S (0.017)
 (Na/K
 ratio)

 Salinity Na/K
 (ppt) ratio ER (%) FCE (%)

 30 25.6 33.30 [+ or -] 4.47 b 19.39 [+ or -] 0.70 b
 34.1 37.85 [+ or -] 0.91 b* 24.76 [+ or -] 0.85 c*
 47.3 36.88 [+ or -] 2.37 b 24.06 [+ or -] 1.01 c
 102.1 32.10 [+ or -] 0.87 b 20.50 [+ or -] 0.58 b
 153.3 22.03 [+ or -] 1.02 a* 15.78 [+ or -] 0.34 a*
 15 25.6 30.19 [+ or -] 1.17 x 20.33 [+ or -] 0.99
 34.1 33.84 [+ or -] 1.00 xy* 22.05 [+ or -] 0.54 *
 47.3 34.89 [+ or -] 1.05 y 22.67 [+ or -] 0.69
 102.1 32.12 [+ or -] 1.32 xy 20.82 [+ or -] 1.06
 153.3 31.34 [+ or -] 0.68 xy* 20.60 [+ or -] 0.44 *
Two-way analysis of varss
 Salinity NS (0.977) NS (<0.422)
 Na/K ratio S (<0.001) S (<0.001)
 Salinity x S (0.009) S (<0.001)
 (Na/K ratio)

 Salinity Na/K
 (ppt) ratio PER

 30 25.6 1.52 [+ or -] 0.06 b
 34.1 1.94 [+ or -] 0.07 c*
 47.3 1.88 [+ or -] 0.08 c
 102.1 1.60 [+ or -] 0.05 b
 153.3 1.24 [+ or -] 0.03 a*
 15 25.6 1.59 [+ or -] 0.08
 34.1 1.73 [+ or -] 0.04 *
 47.3 1.78 [+ or -] 0.05
 102.1 1.63 [+ or -] 0.08
 153.3 1.61 [+ or -] 0.03 *
Two-way analysis of variance ([double dagger])
 Salinity NS (0.934)
 Na/K ratio S (<0.001)
 Salinity x S (0.012)
 (Na/K
 ratio)

FR, feeding rate; PR, protein retention; ER, energy retention; FCE,
food conversion efficiency; PER, protein efficiency ratio.

([dagger]) Mean [+ or -] SE of four replicates. Means within a
column and within each salinity level followed by different letters
are significantly different (Student-Neumann-Keuls multiple comparison,
P < 0.05). Means at the same Na/K ratio level were compared between
salinity 30 and 15 ppt, an (*) following the means indicates
significant difference (P > 0.05).

([double dagger]) Decimal fraction within each bracket denotes the
P value of two-way ANOVA. S, significant (P < 0.05); NS, not
significant (P > 0.05).
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Author:Wang, Fang
Publication:Journal of Shellfish Research
Geographic Code:1USA
Date:Apr 1, 2006
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