CHAPTER FOUR

RESULTS

4.1 General results.

Total number of eggs subjected in the experimental unit were 140eggs per litre in 10litres aquarium. The general trend of results indicated reduction in egg incubation time in increased temperature and salinity combinations. Mean hatching percentage followed the general trend of decrease in increasing temperature and salinity. The increasing in salinity and temperature reduced larval survival in different stages at the early larval stages of P. monodon. Growth and development indicated that early developmental stages of P. monodon are principally affected by salinity though temperature had effect on the same. Cumulative effect indicated the existence of the interaction between temperature and salinity in larval survival. At later postlarval stages there was interacting effects of temperature and salinity on survival and growth centrally to larval stages which didn’t show interacting mode in some larval stages. Temperature salinity and their interactions had significant effect on growth and survival as evidenced by performance index. However, performance index from larvae and postlarval stages was an indication that salinity principally determined growth and survival of the early P.monodon developmental stages.

4.2 Effects of temperature and salinity on Penaues monodon eggs incubation time.

Analyses on embryonic development time was done to assess effects temperature and salinity. In general, shorter P. monodon egg incubation time was in high water temperature-salinity combinations while in lower temperature-salinity combinations had long incubation time. The results obtained from the study indicated in 40ppt had shortest eggs incubation time and longest incubation in salinity 30ppt followed by 35ppt through all tested temperatures. Temperature-salinity combinations which had longest mean incubation time was in 270C and 30ppt with an average of 15.9hours. It was followed by 270C and 35ppt 14.5hours and 310C and 30ppt had 14.4hours. The shortest mean incubation time was in temperature-salinity combination of 350C and 40ppt (10.7hours) followed by 350C and 35ppt with and average incubation time of 11.5hours for P. Monodon eggs hatching to 50% nauplii larvae (Figure 1). Statistical analysis by means of two-way ANOVA (Analysis of variance) indicated a significant difference in incubation time in both temperature and salinity (P ; 0.05). Nevertheless, there was no significant interactions between temperature and salinity on egg incubation time (P = 0.4). Turkey’s pairwise comparison test was performed to detect the differences among the means in incubation time to all tested salinities. The result of Tukey’s test indicated a significant difference in egg incubation time among all salinities (P ; 0.05). The Tukey’s test also was used to compare the differences among temperatures and indicated that it was significant between 270C and 350C (P < 0.05), between 310C and 350C (P < 0.05). However, the difference was not significant between 270C and 310C (P < 0.13).

Figure 1: Incubation time of Penaues monodon eggs at different temperature and salinity combination.

4.3 Effects of temperature and salinity on hatching success of Penaues monodon eggs.

The results obtained from this study indicated that high percentage hatching was in salinity 30ppt followed by 35ppt and lowest being 40ppt in all temperatures. In temperature 350C the mean percentage hatching was low in all salinities, followed by 270C, and temperature 310C had high mean percentage hatching in all salinities. The highest temperature-salinity combination of P. monodon mean percentage hatching was at 310C and 30ppt (85.28%), followed by 82.40% of 270C and 30ppt, then 310C and 35ppt having the hatching percentage of 81.90%. The least hatching percentage was 69.45% in temperature-salinity combination of 350C and 40ppt followed by 75.52% in temperature 350C and 35ppt (Figure 2). Statistical analysis by means of two-way ANOVA (Analysis of variance) indicated that the individual effects of both temperature and salinity on hatching success was very significant (P < 0.05). However, there was no significant difference in interaction between temperature and salinity on hatching success of P. monodon eggs (P = 0.28). Generally, hatching of the eggs was principally determined by salinity. Since there was a significant difference in mean hatching percentages which was influence separately by both salinity and temperature, Tukey’s test pairwise comparison test was performed to compare means percentage hatching among the test temperatures and salinities in all experiments. Tukey’s test results indicated temperature 270C and 310C, 270C and 350C and between temperature 310C and 350C were significantly different (P < 0.05). Tukey’s test performed to test differences among experimental salinities 30ppt, 35ppt and 40ppt, indicated significant difference between all salinities 30ppt versus 35ppt, 30ppt versus 40ppt and 35ppt versus 40ppt (P ; 0.05).

Figure 2: Hatching of Penaeus monodon eggs at different temperature and salinity combinations.

4.4 Effects of temperature and salinity on survival of Penaues monodon larval and postlarval stages.

4.4.1 Naupliar larval survival

The general result obtained from the effect of temperature and salinity on nauplii larval survival indicated that there was general low mean percentage survival in 40ppt through all tested temperatures, followed by 35ppt. The highest percentage nauplii survival was in 30ppt in all temperatures. In temperature 350C had the lowest percentage survival compared to other in all experimental salinities, followed by 310C. The highest percentage survival was recorded in temperature 270C in all salinities except in 30ppt. The highest temperature-salinity combination nauplii mean percentage survival was 90.53% in 310C and 30ppt, followed by 90.20% in 270C and 35ppt, then 88.70% of temperature 270C and 30ppt. The lowest nauplii mean percentage survival was 68.57% in 350C and 40ppt followed by 78.01% in 310C and 40ppt (Table 1).

Statistical analysis by means of two-way ANOVA (Analysis of variance) to investigate the combined effects of temperature and salinity in nauplii larval was performed. The result of ANOVA indicated that there was a significant difference in nauplii larvae percentage survival in temperature (P ; 0.05) and salinity (P ; 0.05) and nauplii survival was determined by salinity. However, the difference in interaction between temperature and salinity combinations in all experiments on nauplii survival was not significant (P = 0.22). Furthermore, Tukey’s pairwise comparison test performed to identify the differences among the means in tested temperatures and salinities. The result from the Tukey’s test indicated the difference was significant between temperature 270C and 350C (P ; 0.05) and between temperature 310C and 350C (P = 0.01). The difference between temperature 270C and 310C the mean percentage survival was not significant (P = 0.38). Among salinities, there was a significant difference among salinities 30ppt versus 40ppt (P ; 0.05) and 35ppt versus 40ppt (P ; 0.05), but the difference between 30ppt and 35ppt was not significant (P = 0.58).

Table 1: Survival percentage of Penaues monodon larval stages in different temperature and salinity combinations (Mean ± Standard error, n=3).

Temperature(0C) Salinity (ppt) Naupliar

(N1-PZ1) Protozoea

(PZ-M1) Mysis

(M1-PL1)

27 30 88.7 ± 4.49 74.58 ± 5.17 68.68 ± 4.1

35 90.2 ± 2.79 70.24 ± 2.69 69.0 ± 1.33

40 83.3 ± 1.29 61.54 ± 2.04 58.21 ± 0.7

31 30 90.53 ± 1.08 80.01 ± 1.42 77.71 ± 4.1

35 85.52 ± 2.52 71.3 ± 0.63 60.14 ± 0.94

40 78.01 ± 2.01 57.96 ± 3.42 48.85 ± 5.91

35 30 84.88 ± 1.28 67.51 ± 4.21 63.96 ± 3.45

35 82.34 ± 3.27 61.77 ± 1.13 56.28 ± 1.73

40 68.57 ± 0.54 39.11 ± 1.14 43.04 ± 2.78

4.4.2 Protozoea larval survival

Peneaus monodon protozoea larval survival result from the study indicated highest percentage survival in temperature-salinity combination was 80.01% in temperature 310C and salinity 30ppt followed by 270C/30ppt and 310C/35ppt with mean percentage survival of 74.58% and 71.30% respectively. The lowest protozoeal larvae mean percentage survival was 39.11% recorded in experimental temperature 350C and salinity 40ppt, followed by 56.96% in temperature 310C and salinity of 40ppt (Table 1). Statistical analysis by means of two-way ANOVA (Analysis of variance) indicated that the combination influence of both temperature and salinity on protozoea larval survival was significantly different (P ; 0.05), but their interactions was not significant (P = 0.09). Tukey’s pairwise comparison test was further performed to compare at which temperature or salinity was the mean significantly different from the other on surviving protozoea. The result of Tukey’s test indicated that salinity 30ppt was not significantly different from salinity 35ppt on survival of protozoea larvae (P = 0.09), but salinity 30ppt versus 40ppt and 35ppt versus 40ppt their differences was significant (P ; 0.05). When Tukey’ test was performed to compare P. monodon protozoeal larval mean percentage survival in different temperatures the following results were obtained. In temperature, 270C versus 350C and 270C versus 350C the difference in surviving protozoea larvae was significant (P < 0.05). Also, in temperature 270C and 310C the difference was significant (P = 0.03).

4.4.3 Mysis larval survival

The result from the study indicated that in salinity 30ppt the mean percentage survival was high in 310C and lower in 270C and 350C. Salinity 35ppt and 40ppt had high mean protozoea percentage survival in 270C and lower in 310C and 350C. In all test temperature-salinity combinations, the highest mean percentage mysis larval survival was 77.71% in temperature 310C followed by 69.00% in 310C and 35ppt. The lowest mean percentage larval survival was 43.04% recorded in temperature-salinity combination of 350C and 40ppt, followed by 48.85% in temperature 310C and 40ppt (Table 1). Statistical analysis by means of two-way ANOVA (Analysis of variance) showed that both temperature and salinity significantly influenced mysis larvae survival rate (P < 0.05) and there was no significant interaction between temperature and salinity (P = 0.06). In order to detect difference among means, Tukey’s pairwise comparison test was performed. The results of Tukey’s test indicated that, the difference was significant in salinity 30ppt versus 40ppt (P < 0.05) and 35ppt versus 40ppt (P < 0.05). Nevertheless, significant difference was also between salinity 30ppt and 35ppt (P = 0.01). When temperatures were compared, significant difference was in temperature 270C versus 350C (P < 0.05) and 310C versus 350C (P = 0.01), but the difference was not significance in temperatures 270C versus 310C (P = 0.49).

4.4.4 Effect of temperature and salinity on Penaeus monodon postlarval survival.

General salinity of 40ppt had lower postlarval percentage survival as compared to 30ppt and 35ppt in all tested temperatures (Figure 3). Penaues monodon postlarval survival was high in temperature 310C but lower in 270C and 350C in 30ppt. Temperature 270C was found to have high mean percentage survival in salinity 35ppt as opposed to temperature 310C and 350C which were recorded with lower P. monodon postalrval mean percentage survival. Salinity 40ppt, high percentage survival was recorded in temperature 310C while 270C and 350C showed lower postlarval percentage survival. Following the general trend of P. monodon postlarval survival, the highest mean percentage postlarval survival in all experiments was 77.70% recorded in temperature-salinity combination of 270C and 35ppt, followed by 70.16% of temperature 310C and salinity 35ppt. The least percentage survival was 31.70% recorded in temperature-salinity combination 350C and salinity 40ppt followed by 38.54% and 45.93% in temperature 270C and 310C respectively in the same salinity of 40ppt.

Penaues monodon postlarval survival data were analysed by two-way ANOVA (Analysis of variance). The result from analyses indicated both effects of temperature and salinity to separately influence postlarval survival was significant (P < 0.05) on post larval survival. The interaction between temperature and salinity on P. monodon postlarval survival was also significant (P = 0.01). Tukey’s test was performed to identify the difference in means among salinities and among temperatures. The result from the Tukey’s test indicated no significant difference in P. monodon postlarval percentage survival in salinities 30ppt versus 35ppt (P = 0.4). Furthermore, significant difference in means was detected in salinity 30ppt versus 40ppt (P < 0.05) and 35ppt versus 40ppt (P < 0.05). Both, Temperatures 270C versus 350C and 310C versus 350C was significantly different from each other (P < 0.05). But, the difference was not significant in temperature 270C versus 310C on P. monodon postlarval survival percentages of (P = 0.54). Tukey’s test was also performed on the interacting effects of both temperature and salinity on postlarval survival. The results from Tukey’s test indicated significant interaction in some of the means of temperature-salinity combination while others did not (Appendix 2).

Figure 3: Survival of Penaeus monodon postlarvae in different temperature and salinity combinations.

4.4.5 Cumulative effects of temperature and salinity on survival of P. monodon larval and postlarval (PL1-PL5) stages.

The cumulative effects in larval and postlarval developmental stages obtained in different temperature and salinity combination are presented in figure 5. Larval stages of P. monodon consisted of 3 stages, naupliar, protozoea and mysis larvae. The postalarva stages were from postlarval stage1 (PL1) to stage 5 (PL5). In general, the mean percentage survival in all stages decreased in the increase of temperature and salinity extremes. The trend was the same throughout the early developmental stages in all experiments.

The highest cumulative nauplii mean percentage survival was recorded in temperature 310C and salinity of 30ppt 90.53%, followed by 90.2% in temperature 270C and salinity 35ppt. Lowest mean percentage survival was 68.57% recorded in 350C and 40ppt, followed by 78.02% in 310C and 40ppt. Cumulative protozoea mean percentage survival was high in temperature 310C and salinity of 30ppt 72.45%, followed by temperature 270C in the same salinity with survival of 66.19%. The lowest protozoea mean percentage survival being 26.81% in 350C and 40ppt and 45.08% in temperature 310C in the same salinity. The result recorded from cumulative survival of mysis larvae indicated temperature 310C and salinity 30ppt to have high mean percentage survival of 56.22% and 45.53% in temperature 270C in the same salinity. The lowest cumulative mean percentage mysis larval survival was found in 350C and 40ppt which had 11.55% survival and 21.92% mysis survival in temperature 310C and 40ppt. Postlarvae cumulative mean percentage survival was 39.49% high in 310C and 30ppt followed by 33.96 in 270C and 35ppt. Lowest percentage survival was in temperature 350C and salinity 40ppt with 3.66% and 9.97% in 310C and 40ppt.

Figure 4: Cumulative survival sequence of early developmental stages of P. monodon in different temperature and salinity combinations. Error bars represent standard error.

Regression analysis model was used in analysis of cumulative percentage survival data were analyzed by using their pooled means. This enabled to determine the strength of relationship between separate effect of temperate and salinity on cumulative survival of larval and postlarval stages. Cumulative pooled mean survival of P. monodon developmental stages to determine the relationship between temperature and survival indicated to be high in 270C and low in temperature 350C (Figure 6). Result of regression indicated that 95.3% of nauplii survival variation contributed by temperature but, no significant relationship between survival and and temperature (R2 = 0.953, P = 0.13). Analysis using regression model was also done on protozoea larvae. The result of regression analyses indicated 78.55% of the variation in protozoea survival was due to effect of temperature, but it wasn’t significant (R2 = 0.7855, P = 0.3). Analyses in mysis larval survival stage indicated that 82.46% 0f the variance in P. monodon mysis laral survival was caused by temperature with no significant relationship between temperature and survival (R2=82.46, P = 0.2). Furthermore, postlarvae survival result analysed by regression indicated 73.57% of the difference in survival percentage of postlarvae was due to temperature, but the reletionshi also was not significant (R2 =0.7357, P = 0.3). All P. monodon developmental stages investigated showed a weak negative relationship between temperature and cumulative survival.

Figure 5: Regression analysis of average cumulative percentage survival with different temperatures.

The relationship between salinity and cumulative mean percentage survival was determined using regression model.survival indicated to be high in lower salinity ( 30ppt) and low in high salinity (40ppt) (Figure 7). Result of regression analysis indicated that 87.79% of nauplii survival variation contributed by salinity but, no significant relationship between cumulative survival and salinity (R2 = 0.8779, P = 0.1). The result of regression analyses in protozoeal larval stage indicated 94.33% of the variation in protozoea survival was due to effect of salinityHowever, the difference was not significant (R2 = 0.9433, P = 0.1Analyses in mysis larval survival stage indicated that 98.47 % of the variation in P. monodon cumulative percentage survival due to salinity and the relationship between salitniy and survival was not significant (R2 = 0.9847, P = 0.07). Postlarvae cumulative survival result analysed by regression indicated 91.14% of the difference in survival percentage of postlarvae was influence by salinity, with no not significant relationship between them (R2 =0.9114, P = 0.1). Weak negative relationship on effect salinity on cumulative survival was observed in all P. monodon early developmental stages.

Figure 6: Regression analysis of average cumulative percentage survival with different salinities.

4.6 Effects of temperature on growth and development of P. monodon larvae and postlarval stages.

4.6.1 Naupliar larvae

Growth of P. monodon larvae was measured at the time when 50% of larvae or postlarvae reached the subsequent stage. Immediately hatched nauplii larvae were relatively of equal size in all experiments ranging from 0.31-0.33mm. Significant growth in different temperature-salinity combination was seen when nauplii larvae reached protozoea 1 (PZ1) larval stage. In salinity 40ppt had great mean growth length was 0.48mm in temperature 350C, followed by 0.46mm in 310C and 0.39mm in 270C. Salinity 35ppt, the highest mean growth length was 0.46mm in 350C followed by 0.43mm in 310C and the lowest mean length was 0.37mm in recorded in 270C. The highest mean length protozoea 1 (PZ1) in salinity 30ppt was 0.45mm measured in 310C, followed by 0.43mm in 350C and the least mean length was 0.38mm in 270C. The development time from nauplii larval stage to PZ1 was longer in temperature 270C in all tested salinities (1.5-2hours), followed by 1.5-1.8hours in temperature 310C and shorter development time was recorded in 350C 1-13hours (Table 2, Figure 7).

Growth in total length data in nauplii larval stage were analyzed by two-way ANOVA and the result obtained from the indicated that both temperature and significantly and separately affected growth of nauplii larvae (P ;0.05) and (P = 0.2) respectively. However, the interaction between the two factors on the growth of nauplii to protozoea 1 was not significant (P = 0.3). Tukey’s test was used to compare the among means in both temperature and salinity also their interactions. The significant difference in means growth in total length was between 270C versus 310C and 270C versus 350C (P < 0.05), no significant difference was seen between 310C and 350C (P = 0.04). The difference among the means in all tested salinities was not significant between 30ppt and 35ppt (P < 0.9) and between 30ppt and 40ppt (P = 0.05). But, between salinity 35ppt and 40ppt the difference was significant (P = 0.02).

4.6.2 Protozoeal larvae growth

Penaues monodon protozoea larval growth was recorded from PZ1 to mysis larval stage 1 (M1). The highest growth in total length was record in salinity 40ppt was 2.22mm in temperature 350C, followed by 1.77mm in 310C and 1.76mm in 270C. Salinity 35ppt, the highest mean growth length was 2.02mm in 350C followed by 1.56mm in 310Cand the lowest mean length was 1.31mm in recorded in 270C. The highest mean length mysis 1 (M1) in salinity 30ppt measured and recorded was 1.4mm in 350C, followed by 1.19mm in 310C and the least mean length was 1.04mm in 270C. The time taken to develop from protozoea 1 to mysis 1 was longer in temperature 270C in all tested salinities (4.2-6.2hours), followed by 3.9-5.5hours in temperature 310C and shortest development time was recorded in 350C 3.3-4.3hours (Table 5). Growth in total length data were analyzed by two-way ANOVA and the result obtained from ANOVA indicated that both temperature and salinity significantly affected growth of nauplii larvae (P < 0.05). Nevertheless, the interaction between temperature and salinity on growth of protozoa larvae wasn’t significant (P ; 0.3). Tukey’s test was used to compare the among means in both temperature and salinity. The significant difference in mean growth was in temperature 310C versus 350C (P < 0.05) and 270C versus 350C (P = 0.01), no significant difference was seen between 270C and 350C (P = 0.0.8). The difference among the means in all salinities were significant (P < 0.05).

4.6.3 Mysis larval growth

Penaues monodon mysis larval growth was recorded from mysis 1(M1) to postlarvae stage 1 (PL1). The highest growth in total length of Penaues monodon mysis larvae recorded in salinity 40ppt was 5.02mm in temperature 310C, followed by 4.67mm in 270C and shorter length was 4.16mm in 350C. Salinity 35ppt, the highest mean growth length was 4.68mm in 350C followed by 4.14mm in 310C and the lowest mean length was 3.96mm in recorded in 270C. The highest mean length PL1 in salinity 30ppt measured and recorded was 3.13mm in 350C, followed by 2.92mm in 310C and the least mean length was 2.75mm in 270C. The time taken to develop from mysis1 to PL1 was longer in temperature 270C in all tested salinities (9.1-10.2hours), followed by 8.9-9.3hours in temperature 310C and shortest development time was recorded in 350C 7.3-9.1hours (Table 2, Figure 7). Growth in total length mysis larvae were analyzed by two-way ANOVA and the result obtained of ANOVA indicated that both temperature significantly affected growth of mysis larvae (P < 0.05). Nevertheless, the interaction between the factors on growth of mysis larvae was also significant (P < 0.02). Tukey’s test was used to compare the among means in both temperature and salinity. The significant difference in mean growth was between 270C versus 310C (P ; 0.05) and 270C versus 350C (P = 0.01) no significant difference was seen between 310C and 350C (P = 0.0.8) The difference among the means in all salinities were significant (P ; 0.05). Tukey’s test was used to compare the means of their interactions. The results from the Tukey’s test obtained are as in appendix 3.

4.6.4 Postlarvae growth

Penaues monodon postlarval growth was recorded from postlarval 1(PL1) to postlarvae stage (PL5). Growth in total length was sampled and measured at the end of experiment. The highest growth in mean total length of Penaues monodon postlarval (PL5) recorded in salinity 40ppt 7.89mm in temperature 310C, followed by 7.05mm in 270C and shorter length was 6.64mm in 350C. In salinity 35ppt, the highest mean growth length was 6.86mm in 350C followed by 6.2mm in 350C and the lowest mean length was 5.7mm in recorded in 270C. The highest mean length PL5 in salinity 30ppt measured and recorded was 5.89mm in 350C, followed by 5.24mm in 310C and the least mean length was 4.87mm in 270C. The time taken to develop from PL1 to PL5 was longer in temperature 270C in all tested salinities was 14.2-15.1hours, followed by 13.1-14.1hours in temperature 310C and shortest development time was recorded in 350C 11.2-12.1hours (Table 2, Figure 7). Growth in total length postlarvae (PL5) were analyzed by two-way ANOVA and the result obtained from ANOVA indicated that both temperature significantly affected growth of mysis larvae (P ; 0.05). Nevertheless, the interaction between the factors on growth of mysis larvae was also significant (P ; 0.02). Tukey’s test was used to compare the among means in both temperature and salinity on growth of postlarvae (PL5). The significant difference in mean growth was between 270C versus 310C (P < 0.05) and 270C versus 350C (P < 0.05), no significant difference was seen between mean length in 310C and 350C (P = 0.9) The difference among the means in all salinities were significant (P < 0.05). Tukey’s test was used to compare the means of their interactions. The results of the Tukey’s test obtained are as in the appendix 5.

Table 2: Average total length (mm) (Mean ± Standard error) of larvae and postlarvae development stages.

Temperature Salinity PZ1-length (mm) M1- length (mm) PL1- length (mm) PL5- length (mm)

27 30 0.38 ± 0.01 1.04 ± 0.02 2.75 ± 0.02 4.87 ± 0.06

35 0.37 ± 0.01 1.31 ± 0.16 3.96 ± 0.16 5.7 ± 0.17

40 0.39 ± 0.01 1.76 ± 0.16 4.67 ± 0.09 7.05 ± 0.06

31 30 0.45 ± 0.02 1.19 ± 0.03 2.92 ± 0.02 5.24 ± 0.13

35 0.43 ± 0.01 1.56 ± 0.09 4.14 ± 0.08 6.2 ± 2.03

40 0.46 ± 0.01 1.77 ± 0.02 5.02 ± 0.02 7.89 ± 0.03

35 30 0.43 ± 0.00 1.4 ± 0.04 3.13 ± 0.04 5.89 ± 0.06

35 0.46 ± 0.01 2.02 ± 0.05 4.68 ± 0.05 6.86 ± 0.06

40 0.48 ± 0.01 2.22 ± 0.02 4.16 ± 0.05 6.64 ± 0.13

Figure 7: Average cumulative duration (days) of development of P. monodon larvae and postlarvae in different temperature and salinity combinations. Error bars refers to standard error.

The growth rate of early developmental stages of P. monodon was investigated at protozoeal stage 1 (PZ1) when nauplius larval survival was first determined to termination of each experiment at postlarval stage 5 (PL5). The result from the study indicated low mean growth rate at temperature 270C and 30ppt 0.29mm/day and high rate was 0.46mm/day in salinity 40ppt. Temperature 310C had low mean growth rate in 30ppt 0.33mm/day, but high in 40ppt (0.57mm/day). Furthermore, in temperature 350C 0.44mm/day had low mean growth rate in 30ppt and high in 35ppt. To the termination of all experiment, the mean highest mean growth rate was found in 310C and 40ppt while the lowest in 270C and 30ppt (Figure 8). Analysis by two-way ANOVA indicated significant difference growth rate from protozoea 1 to postlarvae in both temperature and salinity (P < 0.05). The interactions between the two on growth rate was also significant (P < 0.05). Tukey’s test performed to compare the means indicated the significant different among means in all temperature (P ; 0.05). Also, when comparison of means was done in salinities, Tukey’s test indicated significant different among all salinities (P < 0.05). The means in temperature and salinity were also compared with Tukey’s test (Appendix 5).

Figure 8: Interaction effect of temperature and salinity on growth rate of P. monodon larvae and postlarval (PZ1-PL5).

4.6.6 Performance index (PI)

The performance index of temperature and salinity was calculated to determine the integrative responses of both growth and survival on P. monodon at early developmental stages. The high mean performance index was in temperature 310C and salinity of 30ppt (14.75 ± 0.92), temperature 270C and 35ppt (14.49 ± 0.82), temperature 310C and salinity 30ppt (13.15 ± 0.68). Low performance index calculated was in temperature 350C and 40ppt (2.97 ± 0.3), temperature 270C and salinity 40ppt (6.48 ± 0.67) and temperature 310C and 40ppt (7.33 ± 0.83). The temperature-salinity combinations had moderate performance index (Figure 5).

Figure 5: Performance index of Penaeus monodon larval and postlarval developmental stages in different temperature and salinity combinations. Error bars refers to standard error.

Statistical analysis indicated that performance index in growth and survival were significantly influenced by both temperature and salinity interaction between the two factors over integration of both responses were also significant (P ; 0.05). Tukey’s pairwise comparison test was used to compare the means of performance index. The result of the test among temperatures indicated that the significant difference existed among all temperatures (P < 0.05). The difference among the means in salinities was not significant between salinity 30ppt and 35ppt (P = 0.4), but significant in 30ppt versus 40ppt and 35ppt versus 40ppt (P < 0.05). Tukey’s test result of mean interactions as in appendix 4.