Combined effect of temperature, salinity and density on the growth and feed utilization of Nile tilapia juveniles (Oreochromis niloticus)

Combined effect of temperature, salinity and density

on the growth and feed utilization of Nile tilapia

juveniles (Oreochromis niloticus)

Qiang Jun1, Xu Pao2, Wang Haizhen1, Li Ruiwei3 & Wang Hui1

1Fisheries of College of Guangdong Ocean University, Zhanjiang, 524025, China2Freshwater Fisheries Research Center of Chinese Academy of Fishery Sciences, Wuxi, 214081, China3Maonan Sango Tilapia Breeding Base, Maoming, 525024, China

Correspondence: W Hui, Fisheries College of Guangdong Ocean University, Zhanjiang 524025, China. E-mail: whh524@sina.

com

Abstract

Based on Box–Behnken experimental design and

response surface method, the joint effect of temper-

ature (16–36°C), salinity (0–22 ppt) and rearing

density (200–1000 fish.m�3) on the specific

growth rate (SGR) and feed conversion rate (FCR)

of Nile tilapia juveniles were studied under labora-

tory conditions. The entire experiment lasted for

1 month (30 days). Results showed that the linear

and quadratic effects of temperature, salinity on

both growth and feed utilization were highly sta-

tistically significant (P < 0.01). The linear and

quadratic effect of rearing density on the growth

was highly significant (P < 0.01); the linear

effect of rearing density on feed utilization was

significant (P < 0.05), but the quadratic effect

nonsignificant (P > 0.05). Interactions between

temperature and salinity, and between salinity and

rearing density on the growth statistically differed

from zero (P < 0.05). Interactions between temper-

ature and salinity, between temperature and den-

sity on feed utilization was significant (P < 0.05).

Model equations of the growth and feed utilization

on temperature, salinity and density were estab-

lished, with the coefficient of determination being

98.34% for growth and 98.11% for feed utiliza-

tion, and could be applied to projection. The opti-

mal temperature/salinity/density combination was

obtained utilizing statistical optimization approach:

29°C/6 ppt/500 fish.m�3, at which the maximal

specific growth and feed utilization reached

4.228%.d�1 and 0.520 respectively, with the desir-

ability being 0.989.

Keywords: Oreochromis niloticus, combined effect,

specific growth rate, feed conversion rate, response

surface, optimization

Introduction

Temperature, salinity and stocking density, as

important factors that affect the environment of

aquaculture, have significant impact on the

growth, feeding and survival of aquatic organisms

(Ponce-Palafox, Martlnez-Palacios & Ross 1997;

Papoutsoglou, Tziha, Vrettos & Athanasiou 1998).

Some influences of temperature and salinity on the

growth and survival in tilapia have been reported.

For example, Payne and Collinson (1983) found

that when ranging over 5–10 ppt, salinity had no

prohibitive effect on the growth of Nile tilapia.

Salinity tolerance of hybrid tilapias was apparently

higher than of purebreds, and salinity tolerance of

Israeli red tilapia (Oreochromis niloticus 9 O. mos-

sambicus) was superior to that of Nile tilapias

(Watanabe, Kuo & Huang 1985b). Cataldi, Cro-

setti, Come, D’Ovidio and Cataudella (1988)

reported that Nile tilapia survived for a very short

period of time in sea water. Suresh and Lin

(1992b) found that Nile tilapia (O. niloticus) and

Aurea (O. aureus) could grow only in stenohaline

environment. Qiang, Wang, Li and Peng (2009)

found that salinity, when over the range of

0–8 ppt, did not markedly affect the growth of

hybrid tilapia (O. niloticus 9 O. aureus). Tilapia

had stronger tolerance to high temperature. For

instance, Baras, Jacobs and Melard (2001) found

© 2011 Blackwell Publishing Ltd 1

Aquaculture Research, 2011, 1–13 doi:10.1111/j.1365-2109.2011.02938.x

that the average survivals were as high as 64.7%

and 85% respectively at temperatures of 37°C and

35°C. Salinity was also influential on the fecundity

of tilapia, the ova could not be fertilized and fertil-

ized eggs could not be incubated at salinity 32 ppt

(Watanabe, Kuo & Huang 1985a).

Stocking density, as an environmentally stressful

factor, can bear on the physiology by triggering

fish stress and as a result the growth and survival

of cultured species varied. Stocking density also

had appreciable influence on the growth and feed

utilization in tilapia (Al-Jerian 1996; Yi, Kweilin &

Diana 1996; Carro-Anzalotta & Mcginty 2007;

Osofero, Otubusin & Daramola 2007; Uddin, Rah-

man, Azim, Wahab, Verdegem & Verreth 2007).

Reports regarding the effect of stocking density

can be found in other species, such as Acipenser

schrenckii (Shi, Li, Zhuang, Zhang & Lie 2006),

Dicentrarchus labrax (Papoutsoglou et al. 1998),

Solea senegalensis (Salas-Leiton, Anguis, Martın-

Antonio, Crespo, Planas, Infante, Canavate &

Manchado 2010), Paralichthys californicus (Merino,

Piedrahita & Conklin 2007), Gadus morhua (Lam-

bert & Dutil 2001), Scophthalmus maximus (Irwin,

O’Halloran & FitzGerald 1999). However, these

investigations typically examined the effects of sin-

gle factor rather than several factors in concert

with the growth, survival and reproduction. One-

factor-at-a-time experiments have limitations, and

more often than not, are undertaken with other

environmental conditions held identical, results

thereof are therefore short of practical relevancy

(Montgomery 2005).

It is well known that varying environmental

factors interplay with one another (Brien 1994;

Mihelakakis & Kitajima 1994; Doroudi, Southgate

& Mayer 1999). In practical culture environment,

the level of one factor varies the effect of another,

or other factors vary accordingly (Fiess, Kunkel-

Patterson, Mathias, Rileya, Yanceyb P, Hiranoa &

Graua 2007). Report for the combined effect of

temperature, salinity and stocking density on the

growth and feed utilization in tilapia has yet to be

found so far. Although Watanabe, Ernst, Chasar,

Wicklunda and Ollab (1993) and Likongwe, Ste-

cko, Stauffer and Carline (1996) found the interac-

tions between temperature and salinity using full

factorial design, neither were the quadratic effects

of factors examined and nor was the optimal factor

level combination given. In this experiment, the

effect of simultaneous variation in temperature,

salinity and rearing density on the growth and feed

utilization in tilapia using Box–Behnken design will

be examined, and the models of growth and feed

utilization on the factors of interest will be estab-

lished to determine the optimum factor level com-

bination using response surface method. Results of

the study may be instrumental in increasing the

growth performance and feed utilization and in

turn improving the efficiency of tilapia seed pro-

duction by optimizing seed rearing environment.

Materials and methods

Source of subjects

The healthy and unscathed Nile tilapia juveniles,

which are of GIFT (genetically improved farmed

tilapia, 16th generation) strain, coming from the

Maoming Sangao Tilapia Breeding Base, Guang-

dong province, were chosen for the experiment.

Prior to formal experiment, they were reared for a

short period of time (6 days) in indoor aquaria

(150 L) at a temperature of 27 (±1)°C, pH 7.6

(±0.2) and natural photoperiod. During this transi-

tion, aeration was continuously given through a

recirculating water system and puffing feed (crude

protein 30.0%, lipid 8.0%, ash 15.75%, moisture

12.0%) was given thrice per day: in the morning,

at noon and in the afternoon. Feeding amount

was around 12% of body weight.

Acclimation of experimental fish

The gradual temperature acclimation was

employed for the experimental fish cultured in

plastic buckets (50 L), with the temperature

increased or decreased by about 2°C each day.

Gradual salinity acclimation commenced at the

time of their being acclimated to the corresponding

temperatures. As with the temperature acclima-

tion, the salinity was increased by less than 2 each

day. Immersion heater, whose measuring range is

15–50°C (±0.2°C), was used to dictate tempera-

ture. Salinometer (ATAGO S-10E) was used to

measure salinity, which was prepared using the

sea salt. The experimental fish was reared for

7 days under the setups of temperature and salin-

ity to which they had been acclimated.

Factors and responses

Three factors, viz. temperature (T, °C), salinity (S,

ppt) and stocking density (D, fish.m�3) were cho-

© 2011 Blackwell Publishing Ltd, Aquaculture Research, 1–132

Combined effect of temperature, salinity and density Q. Jun et al. Aquaculture Research, 2011, 1–13

sen for the study of their effect on the growth and

feed conversion of tilapia juveniles in the experi-

ment. Based on the outcomes of preliminary trials

and reference to the bibliography concerned, the

maxima of temperature, salinity and density was

set at 36°C, 22 ppt and 1000 fish.m�3 respec-

tively, and the minima at 16°C, 0 and 200 fish.

m�3 respectively. Two responses were determined,

specific growth rate (SGR, %.d�1) and feed conver-

sion rate (FCR), whose formulae are as follows

(Likongwe et al. 1996):

SGR (%.d-1) = [(lnW2 - lnW1)/(t2 - t1)] �100

FCR= (W2 - W1)/F

where W1 and W2 are body weights at the start

(t1) and finish (t2) of the experiment respectively,

and F is total feeding amount.

Experimental management

A total of 51 plastic buckets (100 L) were used to

carry out the experiment, with 50 L tap water suf-

ficiently aerated for 3 days added to each plastic

bucket. Mean weight and length of the experimen-

tal tilapia juveniles were 2.82 g (±0.058) and

4.35 cm (±0.112) respectively, and the difference

in initial weight and length between varying

groups was of no statistical significance (MANOVA,

P > 0.05). After the temperature-salinity combina-

tion for each plastic bucket was adjusted to those

predetermined setups, tilapia juveniles acclimated

as above were put in, with the stocking density

consistent with that in Table 1. These subjects

were fed with the above indexed puffing feed (mean

wet weight 5.506 9 10�3 g per pellet), which

could be afloat on water surface for 3 h. Each feed-

ing persisted for 1 h or so to ensure that they were

fed to satiety, and then leftovers were collected and

counted timely. The precise feeding amount of the

experimental fish could be derived by multiplying

the difference between the total number of pellets

fed and the number of pellets left by the feed

weight per pellet. Consecutive aeration was given

during the whole experimental period. Faeces at

the bottom of plastic buckets were siphoned off on

a daily basis. One third of water was replaced each

day, with the temperature difference before and

after water replacement within limits of ±0.2°C.Dissolved oxygen (D.O.)>5 mg.L�1, ammonia nitro-

gen < 0.003 mg.L�1, nitrite <0.004 mg.L�1, pH

7.6 (±0.2) and natural photoperiod over the entire

experimental phase (30 days).

Experimental design

Box–Behnken design was adopted to study the

joint effects of temperature, salinity and rearing

Table 1 Experimental design and corresponding results (Mean ± SD)

Run

Coded ActualSpecific growth

rate (SGR)%.d�1

Feed conversion

rate (FCR)T S D T/°C S/ppt D/fish.50 L�1

1 1 �1 0 36 0 30 3.652 ± 0.861 0.453 ± 0.122

2 0 �1 1 26 0 50 2.029 ± 0.579 0.437 ± 0.094

3 0 0 0 26 11 30 3.575 ± 0.682 0.492 ± 0.173

4 �1 0 �1 16 11 10 1.126 ± 0.428 0.381 ± 0.102

5 0 0 0 26 11 30 3.548 ± 0.913 0.527 ± 0.133

6 1 0 �1 36 11 10 3.732 ± 0.671 0.422 ± 0.147

7 0 �1 �1 26 0 10 3.645 ± 0.732 0.488 ± 0.214

8 0 1 1 26 22 50 1.204 ± 0.512 0.254 ± 0.083

9 0 0 0 26 11 30 3.776 ± 0.754 0.463 ± 0.206

10 �1 1 0 16 22 30 0.640 ± 0.311 0.205 ± 0.091

11 0 1 �1 26 22 10 1.545 ± 0.427 0.295 ± 0.078

12 1 0 1 36 11 50 3.029 ± 0.812 0.461 ± 0.127

13 1 1 0 36 22 30 2.024 ± 0.479 0.246 ± 0.095

14 �1 0 1 16 11 50 0.840 ± 0.394 0.294 ± 0.116

15 �1 �1 0 16 0 30 1.020 ± 0.510 0.293 ± 0.092

16 0 0 0 26 11 30 3.962 ± 0.942 0.478 ± 0.148

17 0 0 0 26 11 30 3.851 ± 0.516 0.492 ± 0.173

The unit of density was converted to ‘fish.50 L�1’.

© 2011 Blackwell Publishing Ltd, Aquaculture Research, 1–13 3

Aquaculture Research, 2011, 1–13 Combined effect of temperature, salinity and density Q. Jun et al.

density on the growth and feed conversion in tila-

pia juveniles. There were three factors associated

with the experiment, three levels for three factors

each. Low, intermediate and high levels of three

factors were coded as �1, 0 and 1 respectively. A

total of 17 runs were included in the experiment,

with the number of factorial points being 12, cen-

tre points 5 and axial points 0. To obviate the sys-

tematic change in errors, order of these runs were

randomly arranged, with each run having three

replicates (Table 1).

Data processing

The experiment was designed and data for the

temperature-salinity-density combinations were

analysed using STATISTICA (8.0) software. The

form of relationship between the response and the

factors of interest is:

Y = b0 + b1T + b2S + b3D + b4T �S + b5T

�D + b6S �D + b7T2 + b8S2 + b9D2

where Y is response (SGR or FCR); b0 is constant;

b1, b2, b3 are linear effects of temperature, salinity

and density respectively; b4, b5, b6 are interactive

effects between temperature and salinity, between

temperature and density and between salinity and

density respectively; b7, b8, b9 are quadratic effects

of temperature, salinity and density respectively.

All the effects encompassed in the above equa-

tion were estimated using the least squares proce-

dure, with the random error assumed to conform

to the normal distribution whose mean is 0. At

the same time the standard error, significance and

95% confidence interval (CI) were given of these

effects estimated. Coefficient of determination

(unadjusted R2, adjusted R2, predictive R2), per-

centage of the total variation in response

accounted for by regression, was used to gauge

the goodness of fit of the equations constructed to

experimental data and the reliability for prediction.

The variance inflation factor (VIF) was utilized to

detect the presence of multicollinearity harboured

in the above model. Response surface diagrams

and isopleths would be drawn using the data on

the growth and feed conversion to visualize the

impact of factors of interest on the responses. The

equations derived would be simultaneously opti-

mized using response surface method to establish

the optimal factor level combination. Significance

was set at 5%.

Results

Influence of temperature, salinity and density on

the specific growth rate of Nile tilapia juveniles

The experimental data on SGR is presented in

Table 1. From Table 2, P value for model was less

than 0.01, showing high significance of the model

for SGR. No important factors were left out of the

model (P = 0.1493 for the lack-of-fit test). The lin-

ear and quadratic effects of T, S and D were highly

significant (P < 0.01) (Table 3). T 9 S and S 9 D

had significant influence on SGR (P < 0.05),

T 9 D did not (P > 0.05). Since the regression

coefficients were given in terms of coded factors in

Table 3, the effects of different factors could be

paralleled directly. It could be seen that the linear

effect (positive) of T on SGR was greater than the

linear effects of S and D which were all negative.

Following quadratic polynomial regression of T, S

and D on SGR in terms of the natural levels of

three factors was derived:

SGR ¼ �7:3274þ 0:6334Tþ 0:1546Sþ 0:0759D� 0:0028T� S� 0:0005T� Dþ 0:0014S� D

� 0:0092T2 � 0:0082S2 � 0:0016D2

The coefficient of determination (R2) of the

model for SGR was 0.9834, only 1.66% of the

total variation in SGR could not be accounted for,

by the model established, showing that the fit of

the model to data was quite high.

Graphical representations of response surface (a)

and contour (b) are shown in Fig. 1 to help visual-

ize the effects of T and S on SGR. It could be found

that SGR varied curvilinearly with both T and S.

Low temperature–high salinity and low tempera-

ture–low salinity conditions could patently impede

the growth of tilapia juveniles (P < 0.05), whereas

Table 2 Analysis of variance for the effect of tempera-

ture, salinity and density on the specific growth rate

Source SS d.f. MS F-value P-value

Model 25.160 9 2.796 46.054 < 0.0001

Residual 0.425 7 0.061

Lack-of-fit 0.298 3 0.099 3.134 0.1493

Pure error 0.127 4 0.032

Total 25.585 16

R2 = 0.9834, Adjusted R2 = 0.9620, Predictive R2 = 0.8058.



high temperature-low salinity conditions could

greatly facilitate the growth. Under high salinities,

tilapia juveniles grew slowly. Specific growth

rate for low temperature groups was markedly

lower than for high temperature groups at

S = 22 ppt. When T = 29–33°C and S = 2–10 ppt,

tilapia juveniles grew faster, with SGR more than

4.01%.d�1.

Figure 2 shows the effects of S and D on SGR of

tilapia juveniles (a) and the interaction between

these two factors (b) at T = 26°C. Specific growth

rate varied with S and D in a curvilinear way.

Under high salinities and high densities, SGR of

tilapia juveniles was very small. When salinity

was 6 ppt or so and density was around 500 fish.

m�3, tilapia juveniles grew faster, with the SGR

larger than 3.93%.d�1. From Fig. 2, the signifi-

cant interaction between S and D also could be

observed.

The effects of T and D on SGR of tilapia juveniles

are shown in Fig. 3 with S held at 11. Specific

growth rate of tilapia juveniles first increased with

increased T and D, and then decreased when T

and D were beyond 31°C and 450 fish.m�3

respectively. Specific growth rate was more than

3.97%.d�1 when T ranged over 28–34°C and D

over 280–680 fish.m�3. Under those combinations

of low temperature and high density, tilapia juve-

niles grew very slowly. No interaction between T

and D occurred (P > 0.05).

Influence of temperature, salinity and density on

the feed conversion rate of Nile tilapia juveniles

The experimental data on FCR are listed in

Table 1. Statistical significance of the model for

Table 3 Significance, standard error and 95% confidence interval of coefficients in the regression of the specific growth

rate. In the rightmost column was variance inflation factor (VIF)

Term Coefficient S.E. 95%C.I. Low 95%C.I. High P-value VIF

Intercept 3.623 0.110 3.363 3.883 – –

T 1.156 0.081 0.964 1.348 <0.0001 1.076

S �0.585 0.088 �0.793 �0.377 0.0003 1.020

D �0.358 0.088 �0.566 �0.150 0.0048 1.020

T 9 S �0.281 0.111 �0.543 �0.019 0.0391 1.020

T 9 D �0.094 0.111 �0.356 0.168 0.4254 1.020

S 9 D 0.319 0.123 0.027 0.610 0.0361 1.000

T2 �0.742 0.097 �0.972 �0.512 0.0001 1.082

S2 �0.992 0.120 �1.276 �0.708 < 0.0001 1.006

D2 �0.644 0.120 �0.928 �0.361 0.0010 1.006

Regression coefficients were obtained in terms of coded factors.

16.0021.00

26.0031.00

36.00

0.005.50

11.0016.50

22.00

0.40

1.38

2.35

3.32

4.30

Salinity Tem

perature (

°C)

Spec

ific

grow

th ra

te

(% d

ay–1

)

(a)

16.00 21.00 26.00 31.00 36.000.00

5.50

11.00

16.50

22.001.05

1.69

1.69 2.33

3.94

3.38

4.14

Temperature (°C)

Salin

ity

(b)

Figure 1 Response surface plot (a) and contour plot

(b) for the effect of temperature and salinity on specific

growth rate of GIFT (genetically improved farmed

tilapia, 16th generation) tilapia juveniles (D = 600

fish.m�3).



FCR was checked via ANOVA (Table 4), and signifi-

cance, standard errors and 95% CI of model coeffi-

cients in terms of coded factors are summarized in

Table 5. It is evident that the model for FCR was

highly significant (P > 0.01). The value of lack-of-

fit test was nonsignificant (P = 0.6314 > 0.05).

The linear and quadratic effects of T and S on FCR

statistically differed from zero (P < 0.01). The lin-

ear effect of D was significant (P < 0.05), but the

quadratic effect thereof nonsignificant (P > 0.05).

Interactions T 9 S and T 9 D had significant

influence on FCR (P < 0.05), but S 9 D nonsignif-

icant (P > 0.05). As with SGR, T was positively

influential on FCR (Table 5), while S and D all

negatively bore on FCR in terms of the linear

effect. The quadratic model equation of T, S and D

on FCR in terms of actual factors was arrived at:

FCR ¼ �0:1999þ 0:0476Tþ 0:0184S� 0:0027D� 0:003T� S� 0:0002T

� Dþ 0:001S� D� 0:009T2

� 0:0009S2 � 0:0001D2

The goodness of the model can be checked by

the determination coefficient R2. The high value of

R2 for the model of FCR demonstrates that at least

98% of the total variation in FCR can be ascribed

to the three factors of interest and at most 2% of

the total variation in FCR can be explicated by

noises or chance.

The effects of T, S and D on FCR and two-factor

interactions are presented in Figs 4–6. It is appar-

Salinity0.00 5.50 11.00 16.50 22.00

10.00

20.00

30.00

40.00

50.00

2.33

2.87

3.791.82

1.82

3.58

3.22

(b)

Spec

ific

grow

th ra

te(%

day

–1)

Density (fish 50 L –1)

Den

sity

(fis

h 50

L–1)

Salinity

0.005.50

11.0016.50

22.00

10.00 20.00

30.0040.00

50.00

1.40

2.05

2.70

3.35

4.00(a)


(b) for the effect of salinity and density on specific

growth rate of GIFT (genetically improved farmed tila-

pia, 16th generation) tilapia juveniles (T = 26°C).

Spec

ific

grow

th ra

te(%

day

–1)

Tempera

ture (°C)

16.0021.00

26.0031.00

36.00

10.0020.00

30.0040.00

50.00

0.80

1.65

2.50

3.35

4.20


Den

sity

(fis

h 50

L–1

)

(a)

10.0016.00 21.00 26.00 31.00 36.00

20.00

30.00

40.00

50.00

2.33

3.38

2.87

4.053.79

1.86

Temperature (°C)

(b)


(b) for the effect of temperature and density on specific

growth rate of GIFT (genetically improved farmed tila-

pia, 16th generation) tilapia juveniles (S = 11 ppt).



ent from these response surface diagrams (Figs 4–

6a) that FCR of tilapia juveniles varied curvi-

linearly as T, S and D changed linearly. The feed

utilization of the tilapia juveniles was obviously

hampered by the conditions of low tempera-

ture, high salinity and high density. Overall,

when the temperature/salinity/density combina-

tion lay within 30°C/6 ppt/480 fish.m�3 or so,

the feed utilization was better, with FCR at 0.5

(Figs 4–6b).

Optimization

According to Montgomery (2005), the models of

growth and feed utilization obtained were simulta-

neously optimized, and optimal temperature/salin-

ity/density combination was acquired, viz., 29°C/6 ppt/500 fish.m�3. At this optimal factor combi-

nation, the largest predictions of specific growth

rate and FCR were 4.228%.d�1 (95% CI, 3.971–

4.484) and 0.52 (95% CI, 0.497–0.542) respec-

tively, with the desirability function value as high

as 0.989.

Discussion

Linear effects of temperature, salinity and rearing

density

From the present study it is evident that tempera-

ture, salinity and rearing density affect both

growth and feed utilization of tilapia juveniles, but

temperature is the dominant factor. This is appar-

ent in the response surface plots and isopleths

(Figs 1–6), and also in the statistical analysis

(Tables 3, 5) for growth and feed conversion.

Temperature, as a control factor, plays a chief

role in regulating the metabolic rate in fish, and

thereby becomes an important environmental vari-

able influencing fish activities and growth. Within

suitable temperature range, the fish metabolic

intensity typically is positively correlated with tem-

perature, whereas the fish growth and feed utiliza-

tion are closely relevant to metabolism (Yin 1993;

Nurdiani & Zeng 2007). In our experiment, the

growth and feed utilization of tilapia juveniles were

found to increase with the increased temperature

when temperature ranged over 16–32°C and salin-

ity over suitable scope. Under this condition, the

feeding ability of tilapia juveniles is stronger because

of the coordination between in vivo and an ambient

environment, less energy is used by organisms to

adapt to the environment and for maintaining life

activities, and more energy is spent for growth.

Hence increased feed utilization and growth

occurred (Hepher, Liao, Cheng & Hsieh 1983).

When temperature is beyond 32°C, decreasing

trend is manifested with the growth and feed utiliza-

tion, although the feeding of those juveniles contin-

ued to ascend. As ambient temperature shifts out of

Table 4 Analysis of variance for the effect of tempera-

ture, salinity and density on feed conversion rate

Source SS d.f. MS F-value P-value

Model 0.172 9 0.0191 40.376 <0.0001

Residual 0.003 7 0.0005

Lack-of-fit 0.001 3 0.0004 0.633 0.6314

Pure error 0.002 4 0.0006

Total 0.176 16

R2 = 0.9811, Adjusted R2 = 0.9568, Predictive R2 = 0.8826.

Table 5 Significance, standard error and 95% confidence interval of coefficients in the regression of the feed conversion

rate. Variance inflation factor (VIF) was listed in the rightmost column

Term Coefficient S.E. 95% CILow 95% CI High P-value VIF

Intercept 0.484 0.010 0.461 0.507 � �T 0.061 0.007 0.044 0.078 < 0.0001 1.076

S �0.081 0.008 �0.099 �0.063 < 0.0001 1.020

D �0.021 0.008 �0.039 �0.002 0.0326 1.020

T 9 S �0.027 0.010 �0.050 �0.004 0.0292 1.020

T 9 D 0.028 0.010 0.005 0.052 0.0232 1.020

S 9 D 0.003 0.011 �0.023 0.028 0.8249 1.000

T2 �0.069 0.009 �0.089 �0.049 < 0.0001 1.082

S2 �0.106 0.011 �0.131 �0.081 < 0.0001 1.006

D2 �0.016 0.011 �0.041 0.009 0.1794 1.006

Note:Regression coefficients were obtained in terms of coded factors.



the suitable range, the activity of juveniles intensi-

fies, and the basal metabolism thrives, accordingly

feeding increases. But the bulk of the energy pro-

duced may be used for maintaining activities rather

than for growth, thus the growth and feed utiliza-

tion is diminished. Analogous results were also

reported by Azaza, Dhraїef and Kraїem (2008).

If salinity, usually referred to as inhibitive factor,

goes beyond the tolerance level of fish, the energy

produced in metabolism is used much more for

adjusting the osmotic pressure than for growth

(Boeuf & Payanb 2001). In this experiment, it can

be found that salinity influenced the growth and

feed utilization both in a curvilinear fashion.

Under suitable temperature, the specific growth

rate was greater than 4.0%.d�1 when salinity ran-

ged over 6–10 ppt; the growth was notably

retarded at salinities that were higher than

10 ppt. When ambient salinity shifts out of the

suitable range, tilapia juveniles maintain their sur-

vival by actively transferring ions into water by

increasing the activity of Na+-K+ ATPase in gill fil-

aments. As salinity increases, the number of ions

to be transferred also increases, and thereby the

energy consumed in the osmotic pressure regula-

tion climbs (Sardella, Cooper, Gonzalez & Brauner

2004). This has been documented in other species,

such as Scopthalmus maximus by Gaumet, Boeuf,

Severe, Roux and Mayer-Gostan (1995), Pomacan-

thus imperator by Woo and Chung (1995) and

Oncorhynchus kisutch by Morgan and Iwama

16.0021.00

26.0031.00

36.00

0.005.50

11.0016.50

22.00

0.19

0.27

0.35

0.44

0.52

Tempera

ture (°C)

Salinity

Feed

con

vers

ion

rate

(a)

Temperature (°C)

Salin

ity

16.00 21.00 26.00 31.00 36.000.00

5.50

11.00

16.50

22.000.25

0.36

0.36

0.41

0.47

0.50

0.51

(b)


(b) for the effect of temperature and salinity on feed

conversion rate of GIFT (genetically improved farmed

tilapia, 16th generation) tilapia juveniles (D = 600 fish.

m�3).

(a)

16.0021.00

26.0031.00

36.00

10.0020.00

30.0040.00

50.00

0.28

0.34

0.39

0.45

0.50

Tempera

ture (°C)Density (fish 50 L –1)

Den

sity

(fis

h 50

L–1

)Fe

ed c

onve

rsio

n ra

te

Temperature (°C)16.00 21.00 26.00 31.00 36.00

10.00

20.00

30.00

40.00

50.00

0.36

0.41 0.470.47

0.49

0.50

(b)


(b) for the effect of temperature and density on feed

conversion rate of GIFT (genetically improved farmed

tilapia, 16th generation) tilapia juveniles (S = 11 ppt).



(1998). Imsland, GUstavsson, Gunnarsson, Gun-

narsson, Foss, Arnason, Arnarson, Jonsson, Smar-

adottir and Thorarensen (2008) found that due to

the diminution in the ability to regulate osmotic

pressure, metabolic rate and energy consumed, the

growth for Hippoglossus hippoglossus reared in low-

salinity environment was faster than that in high-

salinity environment. Fiess et al. (2007) reported

that as temperature and salinity increased, envi-

ronmental stress would give rise to the decrease in

the immune function in Tilapia mossambica and

increase in the content of some organic substances

associated with osmotic pressure adjustment. Lee

and Fielder (1981) found that at salinity 6.6 ppt

the concentration of plasma electrolytes (Na+, K+

etc.) increased, while at salinity 10.9 the concen-

tration of plasma electrolytes was out of control in

Macrobrachium ausraliense. Consequently, when

juveniles are cultured in unsuitable environment

for long time, the growth and feed utilization may

be reduced accordingly. Tilapia juveniles must

absorb salts from the environment to keep the

equilibrium of internal osmotic pressure at lower

salinities. Watanabe et al. (1993) found that the

energy used for adjusting osmotic pressure for red

tilapia in freshwater was higher than that in

brackish water (salinity 12–15 ppt). In practical

operations, salinity should be properly increased to

facilitate growth and feed utilization of tilapia juve-

niles.

Rearing density is also an important factor in

tilapia factory production (Huang & Chiu 1997).

Osofero et al. (2007) reported that when ranging

between 50–200 fish.m�3, density had no signifi-

cant influence on the growth, survival and feed

conversion of Nile tilapia. Al-Jerian (1996) found

that the incremental weight (%) of Nile tilapia

declined with increased rearing density, and

growth was greatest at a density of 150 fish.m�3.

Dambo and Rana (1993) found that the optimal

rearing density of Nile tilapia fry (mean 10.56 g)

was 500–1000 fish.m�3. In our experiment, when

stocking density of tilapia juveniles (mean 2.82 g)

varied within 200–1000 fish.m�3, the specific

growth rate also varied curvilinearly with stocking

density, as is akin to that by Dambo and Rana

(1993). As the density escalated further, stress

which arose from the competition for space and

feed also increased, and in turn the growth and

feed utilization were unfavourably affected. Similar

findings have been reported in other species, e.g.,

Salvelinus alinus (Christiansen, Svendsen & Jobling

1992), red tilapia (Suresh & Lin 1992a), Salvelinus

fontinalis (Marchand & Boisclair 1998), Mithrax

caribbaeus (Larez, Palazon-Fernandez & Bolanos

2000), Acipenser schrenckii (Zhuang, Li, Wang,

Zhang, Zhang & Zhang 2002), Pelteobagrus fulvi-

draco (Yang, Yao, Su, Yan & Pan 2007). However,

Wedemeyer (1976) thought that decreased feed

utilization was not enough to explicate the growth

retardation in fish. The mechanism for this issue

has yet to be studied further.

Interactive effects among three factors

When environmental factors change, adaptive

reaction will occur within organisms by virtue of a

particular balance regulation mechanism. Altera-

Feed

con

vers

ion

rate

Salinity

0.005.50

11.0016.50

22.00

10.0020.00

30.0040.00

50.00

0.26

0.33

0.39

0.46

0.52


Den

sity

(fis

h 50

L–1

)

(a)

0.00 5.50 11.00 16.50 22.0010.00

20.00

30.00

40.00

50.00

0.36

0.41

0.49

0.45

0.45

0.50

Salinity

(b)


(b) for the effect of salinity and density on feed conver-

sion rate of GIFT (genetically improved farmed tilapia,

16th generation) tilapia juveniles (T = 26°C).



tions at the biochemical, physiological and

behavioural levels may be encompassed in this

type of reaction (Spanopoulos-Hernandez, Martl-

nez-Palacios, Vanegas-Perez, Vanegas-Perezc,

Rosasd & Ross 2005). The temperature-salinity

interactive effect was also investigated in addition

to having the linear effect of factors of interest

examined in this experiment. Interaction between

temperature and salinity on the growth and feed

utilization of tilapia juveniles were found to be sig-

nificant (Tables 3, 5), as is consistent with some

revelations by Watanabe et al. (1993) and Lik-

ongwe et al. (1996), also with those from other

species, e.g., Perca fluviatilis (Hilden & Hirvi 1987),

Scophthalmus maximus (Imsland, Foss, Gunnarsson,

Berntssen, FitzGerald, Bongad, Hamd, Nævdala &

Stefanssona 2001), Paralichthys dentatus (Malloy &

Targett 1991) and Anarhichas minor (Magnussen,

Imsland & Foss 2008). The isosmotic point of fish

varies with temperature. Under suitable tempera-

ture, less energy is used for osmotic pressure regu-

lation and ion transfer, when ambient salinity is

around the isosmotic point (Martinez-Palacios,

Rossb & Rosado-Vallado 1990) and the perfor-

mance of fish will be brought into play to a

greater extent. As discussed above, the activity of

Na+-K+ ATPase in gill filaments varies with

increased temperature. This will lead to an

increase in intensity of ions infiltrating somatic

fluid, and thereby change in isosmotic point

(Dang, Balm, Flik, Bonga & Lock 2000).

Apart from the temperature-salinity interaction,

other interactions, which have not been reported

so far, were found to be significant. In the experi-

ment, there existed significant interaction between

salinity and density on growth (Table 3). When

temperature was fixed at 26°C, the maxima of

the specific growth rate that varied with different

salinities depended upon density (Fig. 2). The

synergistic influence of the change in living space

caused by density and that in osmotic pressure

brought about by salinity may be responsible for

this result. The interactive effect between temper-

ature and rearing density also had a significant

effect on the feed utilization (Table 5). It can be

seen clearly from Fig. 5 that the maximal FCR

that varied with varying densities, hinged upon

temperature. At lower densities, tilapia juveniles

grow better owing to relatively sufficient food and

larger survival space, while at higher densities,

the feeding ability for those juveniles at higher

temperatures would be stronger, and thus feed

utilization may be relatively higher (Fuiman &

Ottey 1992).

Quadratic effects of three factors

It is found for the first time in our study that the

quadratic effects of temperature, salinity and stock-

ing density on the growth of tilapia juveniles were

highly significant; and the quadratic effects of tem-

perature and salinity were highly significant on the

feed conversion excepting the quadratic effect of

stocking density on feed conversion being nonsig-

nificant (Tables 3 and 5). This is of great practical

significance, because the growth and feed utiliza-

tion of tilapia juveniles would decrease markedly in

a curvilinear way with the simultaneous change in

temperature, salinity and rearing density apart

from the optimal factor level combination regime.

Particular steps, therefore, should be taken in tila-

pia seed production to keep the factor combination

at optimal level as suggested in our study to guar-

antee the maximal production efficiency.

The establishment of model equations

Model equations of specific growth rate and FCR

on temperature, salinity and stocking density were

obtained using Box–Behnken design in this study,

with the determination coefficients as high as

0.9834 and 0.9811 respectively, showing the

excellent fit of them to experimental data. Coupled

with the results of lack-of-fit test, it can be said

that the models derived in this study are of great

adequacy. The predictive coefficients of determina-

tion for the two equations were 0.8058 and

0.8826 respectively, indicating that they can be

practically applied. In terms of corrected determi-

nation coefficient values, the goodness of fit for the

two models is roughly identical, but from the per-

spective of prediction, the projections of the model

equation for feed utilization should be more pre-

cise.In addition, due to all VIFs listed in Tables 3

and 5 being equal to 1, those terms that were

nonsignificant in the two models can be expelled

directly to simplify models derived. This does not

affect the goodness of fit and prediction of the

models.

Simultaneous optimization of two responses

To attain the optimal factor level combination, the

two model equations obtained in the study were



simultaneously optimized according to Montgom-

ery (2005). The optimal temperature/salinity/den-

sity level combination was 29°C/6 ppt/500 fish.

m�3, at which the maximal specific growth and

feed utilization were 4.228%.d�1 and 0.520,

respectively, with the desirability being 0.989. It

should be pointed that unlike those optimal values

derived in the studies cited above, the optimal

factor level combination derived in this study com-

pletely predicated upon the simultaneous optimiza-

tion of the models that are of great adequacy and

can be utilized in practice for prediction.

Finally it should be pointed that owing to the

pre-experimental acclimation of those tilapia juve-

niles, the survival percentage was at least 98%

during the whole experimental period, thus the

side effect caused by the change in rearing density

could be dismissed. Generally, tilapias stop feeding

below 15°C, but because of tilapia juveniles being

well-acclimated prior to the formal experiment,

they still could ingest a small amount of feed at

16°C. In addition, the combined influences of

other environmental factors such as dissolved oxy-

gen, nitrite and photoperiod, on the growth and

feed utilization efficiency should also be examined

to provide the tilapia seed production with more

scientific guidelines.

Acknowledgments

The authors are grateful to the Maonan Sangao

Tilapia Breeding Base, Maoming, Guangdong prov-

ince, for providing them with experimental site

and materials, and also to the assistant manager,

H. S. Liang, for his technical suggestions given

during the trial. The study was supported by the

following grants, the National Science & Technol-

ogy Pillar Program (No. 2008BADB9B01-3), the

Industry-University-Institute Union Program from

Science & Technology Bureau of Guangdong prov-

ince (No. 2008B090500088), and the R&D Spe-

cial Fund for Public Welfare Industry (Agriculture)

(No. 200903046-02).Finally, anonymous review-

ers are greatly appreciated for their excellent sug-

gestions.

References

Al-Jerian A.A. (1996) Effect of stocking density on

growth of the Nile tilapia, Oreochromis niloticus (L.)

reared in glass cages. Pakistan Journal of Zoology 28,

621–626.

Azaza M.S., Dhraїef M.N. & Kraїem M.M. (2008) Effects

of water temperature on growth and sex ratio of juve-

nile Nile tilapia Oreochromis niloticus (Linnaeus) reared

in geothermal waters in southern Tunisia. Journal of

Thermal Biology 33, 98–105.

Baras E., Jacobs B. & Melard C. (2001) Effect of water

temperature on survival, growth and phenotypic sex of

mixed (XX–XY) progenies of Nile tilapia Oreochromis

niloticus. Aquaculture 192, 187–199.

Boeuf G. & Payanb P. (2001) How should salinity influ-

ence fish growth? Comparative Biochemistry and Physiol-

ogy 130, 411–423.

Brien C.J.O. (1994) The effects of temperature and salin-

ity on growth and survival of juvenile tiger prawns

Penaeus esculentus (Haswell). Journal of Experimental

Marine Biology and Ecology 183, 133–145.

Carro-Anzalotta A.E. & Mcginty A.S. (2007) Effects of

stocking density on growth of tilapia nilotica cultured

in cages in ponds. Journal of the World Aquaculture Soci-

ety 17, 52–57.

Cataldi E., Crosetti D., Come G., D’Ovidio D. & Cataudella

S. (1988) Morphological changes in the eosophageal

epithelium during adaptation to salinities in Oreochr-

omis mossambicus, O. niloticus and their hybrid. Journal

of Fish Biology 32, 191–196.

Christiansen J.S., Svendsen Y.S. & Jobling M. (1992) The

combined effects of stocking density and sustained

exercise on the behaviour, food intake, and growth of

juvenile Arctic chart (Salvelinus alinus L.). Canadian

Journal of Zoology 70, 115–122.

Dambo W.B. & Rana K.J. (1993) Effect of stocking den-

sity on growth and survival of Oreochromis niloticus (L.)

fry in the hatchery. Aquaculture Research 24, 71–80.

Dang Z.C., Balm P.H.M., Flik G., Bonga S.E.W. & Lock R.

A.C. (2000) Cortisol increases Na+/K+-ATPase density

in plasma membranes of gill chloride cells in the fresh-

water tilapia Oreochromis mossambicus. Journal of Exper-

iment Biology 203, 2349–2355.

Doroudi M.S., Southgate P.C. & Mayer R.J. (1999) The

combined effects of temperature and salinity on

embryos and larvae of the black-lip pearl oyster, Pinct-

ada margaritifera (L.). Aquaculture Research 30, 271–

277.

Fiess J.C., Kunkel-Patterson A., Mathias L., Rileya L.G.,

Yanceyb P H., Hiranoa T. & Graua E.G. (2007) Effects

of environmental salinity and temperature on osmo-

regulatory ability, organic osmolytes, and plasma hor-

mone profiles in the Mozambique tilapia (Oreochromis

mossambicus). Comparative Biochemistry and Physiology

146, 252–264.

Fuiman L.A. & Ottey D.R. (1992) Temperature effects on

spontaneous behavior of larval and juvenile red drum

Sciaenops ocellatus, and implications for foraging. Fish

Bulletin US 91, 23–35.

Gaumet F.G., Boeuf A., Severe A., Roux A.L. & Mayer-

Gostan N. (1995) Effects of salinity on the ionic



balance and growth of juvenile turbot. Journal of Fish

Biology 47, 865–876.

Hepher B., Liao I.C., Cheng S.H. & Hsieh C.S. (1983)

Food utilization by red tilapia-effects of diet composi-

tion, feeding level and temperature on utilization

efficiencies for maintenance and growth. Aquaculture

32, 255–275.

Hilden M. & Hirvi J.P. (1987) The survival of larval

perch, Perca fluviatilis L., under different combinations

of acidity and duration of acid conditions, analyzed

with a generalized linear model. Journal of fish biology

30, 667–677.

Huang W.B. & Chiu T.S. (1997) Effects of stocking den-

sity on survival, growth, size variation, and production

of Tilapia fry. Aquaculture Research 28, 165–173.

Imsland A.K., Foss A., Gunnarsson S., Berntssen M.H.G.,

FitzGerald R., Bongad S.W., Hamd E.V., Nævdala G. &

Stefanssona S.O. (2001) The interaction of tempera-

ture and salinity on growth and food conversion in

juvenile turbot (Scophthalmus maximus). Aquaculture

198, 353–367.

Imsland A.K., GUstavsson A., Gunnarsson S., Gunnars-

son S., Foss A., Arnason J., Arnarson I., Jonsson A.F.,

Smaradottir H. & Thorarensen H. (2008) Effects of

reduced salinities on growth, food conversion efficiency

and blood physiology in juvenile Atlantic halibut (Hip-

poglossus hippoglossus L.). Aquaculture 274, 254–259.

Irwin S., O’Halloran J. & FitzGerald R.D. (1999) Stocking

density, growth and growth variation in juvenile tur-

bot, Scophthalmus maximus (Rafinesque). Aquaculture

178, 77–88.

Lambert Y. & Dutil J.D. (2001) Food intake and growth

of adult Atlantic cod (Gadus morhua L.) reared under

different conditions of stocking density, feeding fre-

quency and size-grading. Aquaculture 192, 233–247.

Larez M.B., Palazon-Fernandez J.L. & Bolanos C.J. (2000)

The effect of salinity and temperature on the larval

development of Mithrax caribbaeus Rathbun, 1920

(Brachyura: Majiidae) reared in the laboratory. Journal

of Plankton Research 22, 1855–1869.

Lee C.L. & Fielder D.R. (1981) The effect of salinity and

temperature on the larval development of the freshwa-

ter prawn, Macrobrachium ausraliense Holthuis, 1950

from south eastern Queensland, Australia. Aquaculture

26, 167–172.

Likongwe J.S., Stecko T.D., Stauffer J.R. & Carline R.F.

(1996) Combined effects of water temperature and

salinity on growth and feed utilization of juvenile Nile

tilapia Oreochromis niloticus (Linneaus). Aquaculture

146, 37–46.

Magnussen A.B., Imsland A.K. & Foss A. (2008) Interac-

tive effects of different temperatures and salinities on

growth, feed conversion efficiency, and blood physiol-

ogy in juvenile spotted wolffish, Anarhichas minor

Olafsen. Journal of the World Aquaculture Society 39,

804–811.

Malloy K.D. & Targett T.E. (1991) Feeding, growth and

survival of juvenile summer flounder Paralichthys dent-

atus: experimental analysis of the effects of temperature

and salinity. Marine Ecology Progress Series 72, 213–

223.

Marchand F. & Boisclair D. (1998) Influence of fish den-

sity on the energy allocation pattern of juvenile brook

trout (Salvelinus fontinalis). Canadian Journal of Fisheries

and Aquatic Sciences 55, 796–805.

Martinez-Palacios C.A., Rossb L.G. & Rosado-Vallado M.

(1990) The effects of salinity on the survival and

growth of juvenile Cichlasoma urophthalmus. Aquacul-

ture 91, 65–75.

Merino G.E., Piedrahita R.H. & Conklin D.E. (2007) The

effect of fish stocking density on the growth of Califor-

nia halibut (Paralichthys californicus) juveniles. Aquacul-

ture 265, 176–186.

Mihelakakis A. & Kitajima C. (1994) Effects of salinity

and temperature on incubation period, hatching rate,

and morphogenesis of the silver sea bream, Sparus sar-

ba (ForskAl, 1775). Aquaculture 126, 361–371.

Montgomery D.C. (2005) Design and Analysis of Experi-

ments (6th edn). pp. 405–444. John Wiley & Sons,

Inc., New York, USA.

Morgan J.D. & Iwama G.K. (1998) Salinity effects on

oxygen consumption, gill Na+, K+-ATPase and ion reg-

ulation in juvenile coho salmon. Journal of Fish Biology

53, 1110–1119.

Nurdiani R. & Zeng C.S. (2007) Effects of temperature

and salinity on the survival and development of mud

crab, Scylla serrata (Forsska), larvae. Aquaculture

Research 38, 1529–1538.

Osofero S.A., Otubusin S.O. & Daramola J.A. (2007) Effect

of stocking density on tilapia (Oreochromis niloticus

Linnaeus 1757) growth and survival in bamboo-net

cages trial. Journal of Fisheries International 2, 182–185.

Papoutsoglou S.E., Tziha G., Vrettos X. & Athanasiou A.

(1998) Effects of stocking density on behavior and

growth rate of European sea bass (Dicentrarchus labrax)

juveniles reared in a closed circulated system. Aquacul-

tural Engineering 18, 135–144.

Payne A.I. & Collinson R.I. (1983) A comparison of the

biological characteristics of Sarotherodon niloticus (L.)

with those of Surotherodon nureus (Steindachner) and

other tilapia of the Delta and lower Nile. Aquaculture

30, 335–351.

Ponce-Palafox J., Martlnez-Palacios C.A. & Ross L.G.

(1997) The effects of salinity and temperature on the

growth and survival rates of juvenile white shrimp,

Penaeus vannamei, Boone, 1931. Aquaculture 157,

107–115.

Qiang J., Wang H., Li R.W. & Peng J. (2009) Effects

of salinities on growth, survival and digestive

enzymes activity of larval hybrid tilapia (Oreochromis

niloticus9O.aureus). South China Fisheries Science 5,

8–14.



Salas-Leiton E., Anguis V., Martın-Antonio B., Crespo D.,

Planas J.V., Infante C., Canavate J.P. & Manchado M.

(2010) Effects of stocking density and feed ration on

growth and gene expression in the Senegalese sole

(Solea senegalensis): potential effects on the immune

response. Aquaculture 28, 296–302.

Sardella B.A., Cooper J., Gonzalez R.J. & Brauner C.J.

(2004) The effect of temperature on juvenile Mozam-

bique tilapia hybrids (Oreochromis mossambicus 9 O.

urolepis hornorum) exposed to full-strength and hypers-

aline seawater. Comparative Biochemistry and Physiology

137, 621–629.

Shi X.T., Li D.P., Zhuang P., Zhang X.Z. & Lie F. (2006)

Effects of rearing density on juvenile Acipenser

schrenckii digestibility, feeding rate and growth. Chinese

Journal of Applied Ecology 17, 1517–1520.

Spanopoulos-Hernandez M., Martlnez-Palacios C.A.,

Vanegas-Perez R.C., Vanegas-Perezc R.C., Rosasd C. &

Ross L.G. (2005) The combined effects of salinity and

temperature on the oxygen consumption of juvenile

shrimps Litopenaeus stylirostris (Stimpson, 1874). Aqua-

culture 244, 127–138.

Suresh A.V. & Lin C.K. (1992a) Tilapia culture in saline

waters: a review. Aquaculture 106, 201–226.

Suresh A.V. & Lin C.K. (1992b) Effect of stocking density

on water quality and production of red tilapia in a

recirculated water system. Aquaculture 11, 1–22.

Uddin M.S., Rahman S.M.S., Azim M.E., Wahab M.A.,

Verdegem M.C.J. & Verreth J.A.J. (2007) Effects of

stocking density on production and economics of Nile

tilapia (Oreochromis niloticus) and freshwater prawn

(Macrobrachium rosenbergii) polyculture in periphy-

ton-based systems. Aquaculture Research 38, 621–626.

Watanabe W.O., Kuo C.M. & Huang M.C. (1985a) The

ontogeny of salinity tolerance in the tilapias Oreochr-

omis aureus, O. niloticus, and an O.mossambicus 9 O.nil-

oticus hybrid, spawned and reared in freshwater.

Aquaculture 47, 353–367.

Watanabe W.O., Kuo C.M. & Huang M.C. (1985b) Salin-

ity tolerance of Nile tilapia (Oreochromis niloticus)

spawned and hatched at various salinities. Aquaculture

48, 159–176.

Watanabe W.O., Ernst D.H., Chasar M.P., Wicklunda R.I.

& Ollab B.L. (1993) The effects of temperature and

salinity on growth and feed utilization of juvenile, sex-

reversed male Florida red tilapia cultured in a recircu-

lating system. Aquaculture 112, 309–320.

Wedemeyer G.A. (1976) Physiological response of juve-

nile coho salmon (Oncorhynchus kisutch) and rainbow

trout (Salmo gairdneri) to handling and crowding stress

in intensive fish culture. Journal of the Fisheries

Research Board of Canada 33, 2699–2702.

Woo N.Y.S. & Chung K.C. (1995) Tolerance of Pomacan-

thus imperator to hypoosmotic salinities: changes in

body composition and hepatic enzyme activities. Jour-

nal of Fish Biology 47, 70–81.

Yang Y.O., Yao F., Su N.N., Yan Y.Y. & Pan Y. (2007)

Influence of fish density on growth, feed utilization

and energy budget of juvenile Yellow Catfish, Pelteo-

bagrus fulvidraco. Feed industry 28, 31–33.

Yi Y., Kweilin C. & Diana J.S. (1996) Influence of Nile

tilapia (Oreochromis niloticus) stocking density in cages

on their growth and yield in cages and in ponds con-

taining the cages. Aquaculture 146, 205–215.

Yin M.C. (1993) Fishes Ecology, pp. 38–47. China Agri-

cultural Press, Beijing, China (in Chinese).

Zhuang P., Li D.P., Wang M.X., Zhang Z., Zhang L.Z. &

Zhang T. (2002) Effect of stocking density on growth

of juvenile Acipenser schrenckii. Chinese Journal of

Applied Ecology 13, 735–738.



Documents

Combined effect of temperature, salinity and density on the growth and feed utilization of Nile tilapia juveniles (Oreochromis niloticus)