FISHERY BULLETIN: VOL, 71, NO. I 



20 •€ 



25 'C 



30* C 



40-1 



38- 



36 



34- 



32- 



30- 



28- 



26- 



24- 



22 



20 



I8i 



16 



14 H 



12 



15 16 



— 1 1 — I 1 r 



10 15 20 25 30 



'M} 



r4 '* \t 



— I — I — I — I — I 



10 15 20 25 30 

 SALINITY (%.) 



I 



ttl 



■J^-+- 



 I r I l|^ 



10 15 20 25 30 



Figure 2. — Mean ± one standard deviation and range 

 of days required for Palae-monetes vulgaris larvae to 

 reach the postlarval stage at different temperatures and 

 salinities {5%o excluded) (numbers at the lower end of 

 each range line indicate the number of animals which 

 reached the postlarval stage at those conditions of tem- 

 perature and salinity). 



Table 3. — Mean duration (days) of Palaemonetes vul- 

 garis larval instars at different temperatures. Final in- 

 star treated separately. 



Temperature {°C) 



^ Based on five or fewer larvae. 



VARIATION IN NUMBER OF 

 INSTARS 



Most larvae metamorphosed at the 7th, 8th, 

 or 9th molt, but there was much variation in 

 number of instars. Metamorphosis occurred at 

 the 5th through the 12th molts, and one zoea 

 passed through 12 zoeal instars but never 

 reached the postlarval stage. 



The effects of temperature and salinity (ex- 

 cluding 5/^f because only two postlarvae were 

 obtained there) on the number of larval stages 

 are shown in Figures 3 and 4. Sample sizes were 

 unequal, so an approximate method, the analysis 

 of unweighted means (Snedecor, 1956) was em- 

 ployed to indicate significant effects (Table 4). 

 The effect of salinity was not significant, al- 

 though there appeared to be a slight tendency 



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 O 



a. 



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h- 



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z 



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o 

 q: 



UJ 

 Q. 



Figure 3. — Percentage of animals molting to postlarva 

 at each molt under different conditions of temperature 

 and salinity. 



118 



