SAN'DIFER: LARVAL DEVELOPMENT OF GRASS SHRLMP 



Table 1. — Analysis of variance for differences in survival of Palaemo- 

 netes vulgaris larvae through metamorphosis under different conditions 

 of temperature and salinity. 



Table 2. — Summary of Student-Newman-Keuls' multiple 

 range tests to explain differences in survival of Palae- 

 monetes vulgaris larvae at different temperature and 

 salinity conditions. 



20 "C 



r 

 10 15 20 



SALINITY (%o) 



25 



30 



Figure 1. — Comparison of survival to postlarvae for 

 Palaemonetes vulgaris zoeae reared at different temper- 

 atures and salinities. 



RATE OF DEVELOPMENT 



The effects of temperature and salinity (ex- 

 cluding h'/(c) on the rate of larval development 

 are shown in Figure 2. The effect of temper- 

 ature was pronounced; development at 20°C was 

 much slower than at 25° or 30°C. Mean dur- 

 ation of development (days) ±: one standard de- 

 viation was 30.2 ± 3.8 (range, 23 to 39) at 20°C, 

 16.6 ± 2.7 (range, 14 to 25) at 25°C, and 15.7 

 ± 1.8 (range, 13 to 21) at 30°C. Salinity in- 

 fluenced the rate of development much less than 

 did temperature. Survival in h'/ic salinity oc- 

 curred only at 25°C, where the larvae in ^%, gen- 

 erally required about 1 to 4 more days to pass 

 a given stage than did larvae in higher salinities 

 at the same temperature. Development in lO'/ic 



also tended to be slightly slower than in higher 

 salinities, regardless of the temperature (Fig- 

 ure 2). There was little apparent difference 

 among developmental rates in 15 to Z0'/,(. In 

 general, a Qio (20° and 30°C) of about 1.8 was 

 typical of larval development. 



Mean duration of instars (Table 3) was in- 

 versely related to temperature, reflecting devel- 

 opmental rate. Duration of successive instars 

 tended to increase slightly at 20°C. The second 

 instar was markedly short at 25° and 30°C, 

 and the final instar was of longest duration at 

 all temperatures. Overall mean instar duration 

 (days) ± one standard deviation for animals 

 which completed development was 3.6 ±: 0.8 

 (range, 3 to 7) at 20°C, 2.2 ± 0.7 (range, 1 to 7) 

 at 25 °C, and 1.9 ± 0.6 (range, 1 to 4) at 30 °C. 



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