Here again, results show a broad range of salinity tolerance for 

 postlarvae at Z5" or 30° C. (See accompanying table.) As temperature was 

 lowered, however, the tolerance range was progressively reduced. At 35", 

 some mortality occurred at all five salinity levels, suggesting that this tenn- 

 perature is very near the upper absolute limiting level for postlarvae of this 

 species. 



Number of postlarval brown shrimp surviving various 

 temperature -salinity conditions. Pooled results of two 

 experiments. (10 = 100 percent survival.) 



Temperature (° C.) 



A similar experiment on juvenile brown shrimp showed only 4 per- 

 cent mortality at 13° C. (including all salinity levels) and 8 percent mortality 

 at 35°. Comparison of these figures with those for postlarvae (24 percent at 

 15° and 48 percent at 35°) suggests that juveniles tolerate a broader range of 

 temperature. Increased tolerance to temperature changes might have con- 

 siderable adaptive significance for shrimp of this size, since they are nat- 

 urally exposed to the changeable conditions characteristic of estuarine 

 environments. 



Much additional work of this type is needed, e. g. , (1) repetition of 

 above experiments, (2) testing of salinity and temperature levels which will 

 more closely define limiting levels, (3) tolerance comparisons between species, 

 and (4) testing for acclimation effects. 



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