The growth of juvenile Chinese shrimp, Fenneropenaeus chinensis Osbeck, at constant and diel fluctuating temperatures.

ABSTRACT The growth, food consumption, food conversion efficiency and apparent digestibility coefficient of juvenile Chinese shrimp, Fenneropenaeus chinensis Osbeck (body weight 0.36 [+ or -] 0.04 g) were examined under different temperature regimes. The animals were subjected to 6 constant temperatures of 18[degrees]C, 22[degrees]C, 25[degrees]C, 28[degrees]C, 31[degrees]C and 34[degrees]C and diel fluctuating temperatures of 22 [+ or -]2[degrees]C, 25 [+ or -] 2[degrees]C, 28 [+ or -] 2[degrees]C and 31 [+ or -] 2[degrees]C. The results showed that the growth rate of Chinese shrimp at the constant temperature regimes increased from 18[degrees]C to 31[degrees]C, whereas decreased significantly at 34[degrees]C. The growth rates of shrimp at 22 [+ or -]2[degrees]C, 25 [+ or -] 2[degrees]C and 28 [+ or -] 2[degrees]C were significantly greater than those at the corresponding constant temperatures of 22[degrees]C, 25[degrees]C and 28[degrees]C, respectively, whereas no significant difference was found between 31 [+ or -]2[degrees]C and 31[degrees]C. As compared with those at constant temperature, the mean temperature at which maximum growth rate of shrimp occurred shifted to cooler temperature at diel fluctuating temperatures. The shrimp consumed more food at 25 [+ or -] 2[degrees]C, 28 [+ or -][degrees]C and 31 [+ or -]2[degrees]C than those at 25[degrees]C, 28[degrees]C and 31[degrees]CC, respectively, but no significant difference in apparent digestibility coefficient was found between the fluctuating and corresponding constant temperatures. The food conversion efficiency and energy assimilated into growth as percentage of energy from food for shrimp at 22 [+ or -]2[degrees]C, 25 [+ or -] 2[degrees]C and 28 [+ or -]2[degrees]C were significantly higher than at the corresponding constant temperatures. Therefore, more food consumption, high food conversion efficiency and more energy partitioned into growth might contribute to the enhanced growth rate at the fluctuating temperatures.

KEY WORDS: constant temperatures, diel fluctuating temperatures, growth, energy budget, Fenneropenaeus chinensis, shrimp

INTRODUCTION

Temperature is one of the major physical factors influencing the growth rates of ectotherms. It is well known that the temperatures in natural aquatic systems fluctuate diurnally and seasonally. Most previous studies on the effects of temperatures on the growth of aquatic animals usually have been conducted under constant temperature regimes with an implicit assumption that growth in fluctuating temperatures would be approximated by growth at a constant temperature coinciding with the average temperature of the fluctuation. These studies have led to much insight into the influence of temperature on the growth of aquatic animals, however, the growth response of animals subjected to a fluctuating thermal environment, typical of those normally encountered in nature, would not been examined (Hokanson et al. 1977, Cox & Coutant 1981). For example, the use of average temperature to characterize growth in fluctuating temperature regimes had been questioned by Hokanson et al. (1977).

Until now, many studies have been conducted to investigate the effects of fluctuating temperatures on a variety of aquatic ectotherms, such as zooplankton (Halbach 1973, Van As et al., 1980), bivalves (Widdows 1976, Pilditch & Grant 1999) and crustaceans (Dame & Vernberg 1978, Miao & Tu 1993, Miao & Tu 1996), and most of them focused on fishes (Biette & Geen 1980, Cox & Coutant 1981, Diana 1984, Konstantinov et al. 1989, Lyytikainen & Jobling 1998, Lyytikainen & Jobling 1999, Sierra et al. 1999, Zdanovich 1999, Baras et al. 2000). Because of the differences in species and thermal regimes, the results from different studies were very inconsistent.

Chinese shrimp Fenneropenaeus chinensis (Osbeck 1765) is the most important marine species cultured in China, comprising approximately 80% of the total shrimp production. Chinese shrimp are mainly distributed in the Yellow Sea and usually migrate for reproduction and overwintering twice a year in Bohai Sea, Yellow Sea and East China Sea (Ge & Wang 1995, Miao & Tu 1995). Thus, not only Chinese shrimp have experienced temperatures diurnally and seasonally fluctuations, but also they normally are exposed to varying temperatures when they move in water masses, vertically and horizontally, during feeding, swimming or predator avoidance. Until now, although a lot of studies on the effects of temperatures on the growth of this species have been conducted, most of them have focused on the effects of constant temperatures (Zhang et al. 1983, Wang et al. 1984, Miao & Tu 1995, Zhang et al. 1998), and only a few work dealing with the effect of fluctuating temperature on the growth of shrimp (Miao & Tu 1996) was reported.

In a previous study, it was found that the oxygen consumption of Chinese shrimp at a fluctuating temperature of 27 [+ or -] 3[degrees]C was significantly lower than that at a constant temperature of 27[degrees]C (Tian et al. 2004b), whereas the growth rate of shrimp at 27 [+ or -] 3[degrees]C was significantly higher than at the corresponding constant temperature of 27[degrees]C (Tian 2001), which implicated that there could be a bioenergetic mechanism involved in this difference between fluctuating thermal regimen and corresponding constant temperature. Based on this assumption, this study was designed to evaluate the growth rate, food consumption (FC), food conversion efficiency and energy budget of Chinese shrimp at diel fluctuating temperatures and constant temperature. The physiological and bioenergetic mechanisms involved in the optimization of shrimp growth in fluctuating thermal regimes were also investigated.

MATERIALS AND METHODS

Experimental Shrimp and Acclimation 

Chinese shrimp juveniles were obtained from the pond of the Hongdao Shrimp Farm, Qingdao, P.R. China. The shrimp were cultured in aerated fiberglass tanks with seawater and maintained at about 25[degrees]C for at least 3 days. Then the shrimp were acclimatized to various constant temperature regimes, 18[degrees]C, 22[degrees]C, 25[degrees]C, 28[degrees]C, 31[degrees]C and 34[degrees]C at 1.5[degrees]C per day. When the desired temperature was reached, the shrimp were further kept in the target temperature for three days before the experiment started. During acclimation, the shrimp were fed twice daily to satiation with a commercial pellet manufactured by the Mawei Fishery Feed Co. Ltd., Fujian, China (43.39 [+ or -] 0.22% crude protein, 9.74 [+ or -] 0.30% lipid, 9.91 [+ or -] 0.05% ash, 16.88 [+ or -] 0.11% energy and 8.41 [+ or -] 0.06% moisture). A 14 h light: 10 h dark photoperiod was maintained.

Experimental Design and Facility

The thermal treatments included 6 constant temperatures, 18[degrees]C, 22[degrees]C, 25[degrees]C, 28[degrees]C, 31[degrees]C and 34[degrees]C, and four diel temperature fluctuations with daily means between 22 and 31. There were four replicates for each thermal treatment. In the fluctuating temperature treatments, the pattern of diel temperature fluctuations imitated the daily natural rhythm of field water temperature at the site of the present experiment (36[degrees]1'N, 120[degrees]3'E) and amplitude of temperature fluctuation was set at [+ or -] 2[degrees]C. The minimum temperature was set at 0600 h, and increased gradually to the maximum at 1400 h, then was decreased to the minimum again at 0600 h next day.

During the experiment, the ambient temperature was controlled at 16 [+ or -] 0.5[degrees]C. Four glass aquaria (45 x 25 x 30 cm) were incubated in a water bath tank (170 x 75 x 30 cm) and the temperature of aquaria was controlled by water bath. Each aquarium was covered with a 5-mm screen to prevent the shrimp jumping out of the aquaria. Two recirculating pumps (35 W) were applied in each water bath tank to ensure the even distribution of water temperature in whole tank. Two systems were applied to control different water thermal regimes. The constant temperature was maintained by the thermostatic regulation of immersion heaters (WMZK-01). The actual temperature was daily calibrated with a mercury thermal meter to the nearest 0.1 [degrees]C. In the treatment with fluctuating temperatures, each designated temperature range was controlled by a heating and cooling coil.

Experimental Procedure and Management

After thermal acclimation, 20 shrimp were randomly chosen, weighed individually and stocked into four aquaria for corresponding constant temperature treatment with each aquarium holding five individuals after 24-h feed deprivation. The same procedure was applied to choose shrimp from 22[degrees]C, 25[degrees]C, 28[degrees]C and 31[degrees]C thermal acclimation tanks and stock into aquaria for the diel temperature fluctuations treatments, i.e., 22 [+ or -] 2[degrees]C, 25 [+ or -] 2[degrees]C, 28 [+ or -] 2[degrees]C and 31 [+ or -] 2[degrees]C, respectively. There were four aquaria for each thermal treatment. Ten shrimp were randomly sampled from each corresponding thermal acclimation tank for measurement of initial proximate body composition. During the experiment, the shrimp were fed twice daily to satiation (at 0600 and 1800 h) with commercial pellets. The uneaten feed and feces were separately collected using a siphon tube within 1.5 h after feeding. The collected uneaten feed and feces were settled in a beaker, and then the water above was removed carefully. The exuviae (molted exoskeletons) were collected at times. The uneaten feed, feces and exuviae were dried at 65[degrees]C, respectively, and kept for further analysis. FC was estimated from the difference between the amount of food applied into the aquarium and food uneaten. At the end of the experiment, all the test shrimp were collected after 24-h starvation and dried at 65[degrees]C for 48 h.

The experiment was conducted from May 30, 2000 to July 2, 2000. During the experiment, water exchanges were made to all treatments at the same time. Aeration was provided continuously and one-half to two-thirds of the water volume was exchanged every other day to ensure suitable water quality. Seawater used in the experiment was filtered by composite sand filter. During the course of the experiment, dissolved oxygen was maintained above 6.0 mg/L, the pH was around 7.8, ammonia was less than 0.24 mg/L, salinity of seawater was within 28-30 ppt, and a simulated natural photoperiod (14 L:10 D light/darkness) was maintained.

Determination of Energy Contents and Estimation of Energy Budget

The energy contents of the whole shrimp, feed and feces were measured by the Parr 1281 Oxygen Bomb Calorimeter. The energy budget was calculated as the following equation for the crustacean energy budget (Petrusewicz & Macfadyen 1970):

C = G + F + U + E + R

where, C is the energy consumed in food; G, the energy deposited for growth; F, the energy lost in feces, U, the energy in excretion; E, the energy spent for exuvia, and R, the energy for respiration.

The estimation of U was based on the nitrogen budget equation (Levine & Sulkin 1979, Lemos & Phan 2001):

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

where [C.sub.N] is the nitrogen consumed from food; [F.sub.N], the nitrogen lost in feces; [G.sub.N], the nitrogen deposited in shrimp body; [E.sub.N], the nitrogen lost in molting; 24,830, the constant of energy content in excreted nitrogen (J/g). The nitrogen contents in the formulated feed, shrimp, feces and molting shell were determined by the Kjeldahl method.

The value of R was calculated as the following energy budget equation:

R = C - G - F - U - E

Data Calculation and Statistical Analysis

All indices were calculated as follows: specific growth rate (SGR, %/d) = 100 x (ln Wt - lnWo)/t; food conversion efficiency (FCE, %) = 100 x (Wt-Wo)/C; apparent digestibility coefficient (ADC, %) = 100 x (C-F)/C. where, Wt and Wo are the final and initial weights (g), t is the feeding duration (d), C is daily FC (g), and F is the daily fecal production (g).

Experimental data expressed as aquarium means were analyzed using SPSS 10.0 (SPSS Inc., Richmond, CA, USA), with possible differences among data being tested by the student's t-test and one-way ANOVA. Duncan multiple range test was used to test the differences between treatments. P < 0.05 was accepted as the level of statistical significance. Log transformations were used to homogenize the variance of body weight before data analyses. Arcsine transformations were used for feeding rate, FCE and apparent digestion rate to normalize the data distribution.

RESULTS

The growth rate of Chinese shrimp at constant temperatures increased with the temperatures from 18[degrees]C to 31[degrees]C, whereas it decreased significantly at 34[degrees]C (Table 1 and Fig. 1). Referred to studies of Miao and Tu (1993), the relationship between constant temperature (T,[degrees]C) and SGR of Chinese shrimp was best described by polynomial regression analysis:

SGR = -[0.0028T.sup.3] + [0.1976T.sup.2] - 4.3902T + 32.4816 [R.sup.2] = 0.8217 F = 39.90 n = 24

[FIGURE 1 OMITTED]

The shrimp exhibited different growth trends at diel fluctuating temperatures compared with those at constant temperature regimen (Table 1 and Fig. 1). The daily increment and SGR of shrimp at diel fluctuating temperatures changed from 13.94 mg per day and 2.54% per day to 29.70 mg per day and 4.11% per day, respectively. The growth rates of shrimp at 22 [+ or -] 2[degrees]C, 25 [+ or -] 2[degrees]C and 28 [+ or -] 2[degrees]C were significantly greater than those at the corresponding constant temperatures of 22[degrees]C, 25[degrees]C and 28[degrees]C, respectively, whereas no significant difference was found between 31[degrees]C [+ or -] 2[degrees]C and 31[degrees]C (P < 0.05). The best growth occurred at 28[degrees]C [+ or -] 2[degrees]C under fluctuating temperature regimen, whereas best growth occurred at 31[degrees]C under constant temperature regimen. Thus, from the growth curves of shrimp, it can be seen that the mean temperature at which maximum growth rate of shrimp occurred shifted to cooler temperature at diel fluctuating temperatures as compared with those at constant temperature.

Compared with corresponding constant temperature, FC of shrimp at 25 [+ or -] 2[degrees]C, 28 [+ or -] 2[degrees]C and 31 [+ or -] 2[degrees]C were significantly higher than at corresponding constant temperatures (P < 0.05); however, no significant difference was found between 22 [+ or -] 2[degrees]C and 22[degrees]C (P > 0.05) (Fig. 2).

[FIGURE 2 OMITTED]

There was no difference in ADC between diel fluctuating temperature and corresponding constant temperature (P > 0.05, Fig. 3).

[FIGURE 3 OMITTED]

Food conversion efficiencies of shrimp at fluctuating temperatures of 22 [+ or -] 2[degrees]C, 25 [+ or -] 2[degrees]C and 28 [+ or -] 2[degrees]C were higher than at the corresponding constant temperatures of 22[degrees]C, 25[degrees]C and 28[degrees]C (P < 0.05), respectively, but there was no significant difference between 31[degrees]C and 31 [+ or -] 2[degrees]C (P > 0.05) (Fig. 4).

[FIGURE 4 OMITTED]

Table 2 shows the patterns of energy allocation in the test shrimp at fluctuating temperatures and corresponding constant temperatures. The shrimp at the fluctuating temperatures of 22 [+ or -] 2[degrees]C, 25 [+ or -] 2[degrees]C and 28 [+ or -] 2 [degrees]C assimilated more energy for growth than those at constant temperatures of 22[degrees]C, 25[degrees]C and 28[degrees]C (P < 0.05), respectively, whereas no significant difference was found between 31 [+ or -] 2[degrees]C and 31[degrees]C (P > 0.05). The shrimp at 28 [+ or -] 2[degrees]C spent less energy in respiration than those at 28[degrees]C (P < 0.05). No differences were found between the fluctuating and corresponding constant temperatures in the allocation of consumed energy to feces, excretion and exuvia.

DISCUSSION

The positive influence of fluctuating temperatures on the growth of crustaceans has been reported in cladocerans, copepods, crabs and penaeid shrimp. The development and growth of Daphnia pulex (De Geer), Pseudocalanus minutus (Kroeyer), mud-crab Rhithropanopeus harrissi (Gould), Chinese mitten crab Eriocheir sinensis (H. Milne Edwards), redtail shrimp F. penicillatus (Alcock) and Chinese shrimp increased at moderate diel fluctuating thermal regimes (Lock & Mclaren 1970, Costlow & Bookhout 1971, Van As et al. 1980, Miao & Tu 1993, Miao & Tu 1996, Wang 1999). In this study, the shrimp at fluctuating temperatures of 22 [+ or -] 2[degrees]C, 25 [+ or -] 2[degrees]C and 28 [+ or -] 2[degrees]C exhibited higher growth rate than those at corresponding constant temperatures of 22[degrees]C, 25[degrees]C and 28[degrees]C, and better growth occurred at 28[degrees]C [+ or -] 2[degrees]C. In comparison, the shrimp at 31[degrees]C grew best under constant temperature regimes. Thus, the mean temperature at which maximum growth rate of shrimp occurred shifted to cooler temperature at diel fluctuating temperatures as compared with those at constant temperature, which is similar to results of Hokanson et al. (1977) and Lyytikainen and Jobling (1999) in rainbow trout Salmo gairdneri (Richardson) and Arctic chart Salvelinus alpinus (Linnaeus). The growth rate of shrimp appeared to be accelerated at fluctuating temperatures whose mean temperatures are below the corresponding constant optimum temperature for growth, whereas it retarded at fluctuating thermal regimes whose mean temperatures are above the constant optimum temperature for growth. This result indicated that the diel fluctuations within the range normally selected by shrimp (i.e., physiological optimum and lower) were beneficial to growth. Fluctuations at the mean temperatures above the physiological optimum, however, might inhibit the growth of shrimp.

The mechanisms for the enhancement in growth of crustacean at diel fluctuating temperatures were still investigated less thoroughly. Dame and Vernberg (1978) showed that diel fluctuating temperature regimes significantly depressed oxygen consumption in the 15[degrees]C to 25[degrees]C temperature range in the mud crab Panopeus herbstii (H. Milne-Edwards) and the fiddler crab Uca pugilator (Bosc) when compared with rates of animals subjected to constant acclimation rates. Because this depression of metabolic rates occurs over that portion of the yearly temperature range within which the animals are most active, it is suggested that these organisms use energy more efficiently when subjected to natural cyclic temperature conditions than when subjected to constant temperature environments. Tian et al. (2004b) also obtained the similar result in Chinese shrimp. The oxygen consumption of Chinese shrimp at a fluctuating temperature of 27[degrees]C [+ or -] 3[degrees]C was significantly lower than that at a constant temperature of 27[degrees]C, which could explain the increased growth at same fluctuating temperatures partially (Tian 2001). In this study, increased FC were found in shrimp at fluctuating temperatures of 25[degrees]C [+ or -] 2[degrees]C and 28[degrees]C [+ or -] 2[degrees]C, and better FCE occurred at 22 [+ or -] 2[degrees]C, 25 [+ or -] 2[degrees]C and 28 [+ or -]2[degrees]C, whereas there was no difference in ADC between diel fluctuating temperature and corresponding constant temperature. The study on energy allocation showed that the shrimp at fluctuating temperature of 22 [+ or -] 2[degrees]C, 25 [+ or -] 2[degrees]C and 28 [+ or -] 2[degrees]C partitioned more energy for growth than those at constant temperatures of 22[degrees]C, 25[degrees]C and 28[degrees]C, respectively. Thus, the enhancement in the growth of shrimp in the present study could mainly be ascribed to energetic advantage at optimal diel fluctuating temperatures, high FCE, reduced metabolism and more energy partitioned into growth although more FC might be one of mechanisms for increased growth as well.

ACKNOWLEDGMENTS

The authors thank M. Yang for providing assistance with the design of the experimental facility, and Miss F. Wang, X. Zhang, M. Wan, S. Jiang and G. Liu for providing assistance in the care and maintenance of this experiment. The authors also thank Dr. J. Qin for checking language. This work was supported by the Chinese National Science Foundation for Talent Youths (Grant No. 39725023), the Chinese National Science Foundation (Grant No. 30571441), the Project under the Major State Basic Research of China (Grant no. G 1999012011) and the Key Science and Technology Program of Shandong (Grant no. 012110112).

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XIANGLI TIAN, SHUANGLIN DONG, * FANG WANG AND LIXIN WU

The Key Laboratory of Mariculture, Ministry of Education Fisheries College, Ocean University of China, Qingdao, 266003, People's Republic of China

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

TABLE 1.
Growth of Chinese shrimp at constant and fluctuating temperatures
(mean [+ or -] SE)

                Temperature          No.           Initial
Treatments       [degrees]C        Shrimp         Weight (g)

   CT18            18                20       0.35 [+ or -] 0.02
   CT22            22                20       0.37 [+ or -] 0.01
   CT25            25                20       0.35 [+ or -] 0.02
   CT28            28                20       0.35 [+ or -] 0.02
   CT31            31                20       0.36 [+ or -] 0.02
   CT34            34                20       0.33 [+ or -] 0.04
   FT22      22 [+ or -] 2           20       0.35 [+ or -] 0.03
   FT25      25 [+ or -] 2           20       0.35 [+ or -] 0.06
   FT29      28 [+ or -] 2           20       0.34 [+ or -] 0.02
   FT31      31 [+ or -] 2           20       0.35 [+ or -] 0.01

                   Final          Duration     Daily Increment
Treatments       Weight (g)          (d)          (mg/d.ind)

   CT18      0.52.[+ or -] 0.07      33        5.34 [+ or -] 2.08
   CT22      0.67 [+ or -] 0.06      33        9.10 [+ or -] 0.16
   CT25      0.86 [+ or -] 0.09      33       15.54 [+ or -] 1.85
   CT28      0.96 [+ or -] 0.08      33       18.67 [+ or -] 3.23
   CT31      1.07 [+ or -] 0.08      33       21.43 [+ or -] 0.70
   CT34      0.63 [+ or -] 0.05      33        9.10 [+ or -] 2.08
   FT22      0.81 [+ or -] 0.04      33       13.94 [+ or -] 1.12
   FT25      1.09 [+ or -] 0.08      33       22.42 [+ or -] 1.62
   FT29      1.32 [+ or -] 0.07      33       29.70 [+ or -] 1.67
   FT31      1.23 [+ or -] 0.06      33       26.67 [+ or -] 0.51

CT, constant temperature; FT, fluctuating temperature.

TABLE 2.
Allocation of the consumed energy in Chinese shrimp at
constant
and fluctuating temperatures (mean [+ or -] SE)

                      G/C                      F/C
Treatments             (%)                     (%)

   CT22      13.94 [+ or -] 1.34 (a)   15.59 [+ or -] 1.12
   FT22      18.16 [+ or -] 1.12 (b)   14.81 [+ or -] 1.23
   CT25      13.82 [+ or -] 0.48 (a)   12.04 [+ or -] 0.77
   FT25      15.62 [+ or -] 0.26 (b)   13.56 [+ or -] 1.02
   CT28      12.35 [+ or -] 1.56 (a)   11.73 [+ or -] 1.04
   FT28      17.97 [+ or -] 1.58 (b)   10.43 [+ or -] 0.96
   CT31      12.14 [+ or -] 0.57        8.41 [+ or -] 0.45
   FT31      12.66 [+ or -] 0.21        6.75 [+ or -] 1.54

                       U/C                     E/C
Treatments             (%)                     (%)

   CT22      6.81 [+ or -] 0.15        0.80 [+ or -] 0.09
   FT22      6.05 [+ or -] 1.02        0.63 [+ or -] 0.04
   CT25      7.06 [+ or -] 0.26        0.44 [+ or -] 0.15
   FT25      6.47 [+ or -] 0.28        0.28 [+ or -] 0.03
   CT28      7.03 [+ or -] 0.27        0.51 [+ or -] 0.11
   FT28      6.41 [+ or -] 0.20        0.46 [+ or -] 0.11
   CT31      7.61 [+ or -] 0.06        0.52 [+ or -] 0.01
   FT31      7.80 [+ or -] 0.12        0.41 [+ or -] 0.01

                       R/C
Treatments             (%)

   CT22      62.86 [+ or -] 3.12
   FT22      60.35 [+ or -] 2.41
   CT25      66.64 [+ or -] 1.52
   FT25      64.06 [+ or -] 1.91
   CT28      68.38 [+ or -] 1.44 (a)
   FT28      64.72 [+ or -] 0.55 (b)
   CT31      71.32 [+ or -] 0.41
   FT31      72.38 [+ or -] 1.31

CT, constant temperature; FT, fluctuating temperature. R/C, energy
for respiration/energy consumed in food; G/C, energy for growth/energ
consumed in food; E/C, energy for exuvia/energy consumed in food;
U/C, energy for excretion/energy consumed in food; F/C, energy for
faeces/energy consumed in food. Means with different letters were
significantly different from each other (p < 0.05).