Table 10. Percentage survival of sucmer postlarvae of brown and white shrimp exposed to various 



combinations of salinity and temperature 



■"■ No tests made at combinations indicated by dashes. 



^ j WHITE SHRIMP 



^} enowN SHniHP 



5 10 13 20 



TIME (DAYS) 



25 30 



Figure 39. 



-Growth of brown and white shrimp postlarvae 

 at 77° and 92.5° F. 



at these two temperatures were almost iden- 

 tical both in length and weight. 



At a single temperature, however, salinity 

 did not seem to affect growth in either species. 

 Once again it seems that growth may be af- 

 fected more by the temperature than by the 

 salinity of the environment. Furthermore, 

 the data cited above confirm our earlier work 

 which indicated that combinations of low 

 salinity and low temperature were detrimental 

 to the growth and survival of postlarval 

 brown shrimp. 



Since the growth of postlarval brown shrimp 

 seemed to be influenced far more by tempera- 



ture than by salinity, we made a more ex- 

 haustive study of the effects of temperature 

 upon growth in this species. The effects of 

 early spring temperatures (59° to 77° F.) 

 were reported last year. Animals held at 77° F. 

 for 30 days were almost twice as heavy as 

 those held at 72.5° F. and almost 10 times 

 as heavy as those held at 63.5° F. Because 

 postlarvae arriving in the bays in late spring 

 spend most of their lives at temperatures 

 considerably higher than 77° F., our second 

 study during the summer of 1964 tested the 

 effects of tennperatures of 77° F. through 95° 

 F. The study yielded two notable results: 

 survival was markedly reduced at 95° F., and 

 all experimental animals died within 15 days. 

 In contrast to the early spring study, which 

 indicated a continuous increase in growth as 

 temperature increased up to 77° F., tenn- 

 peratures above 77° had much less effect in 

 increasing growth of brown shrimppostlarvae. 

 This effect of high temperatures on growth 

 in brown shrimp is also suggested by the 

 salinity and temperature study illustrated in 

 figure 39. 



Ecologically, the differences in temperature 

 and salinity tolerance between postlarval brown 

 and white shrimp fit well with the environ- 

 mental conditions actually encountered by 

 most members of each species. Postlarval 

 brown shrimp entering the bays in early 

 spring are subjected to far lower temperatures 

 than those encountered later by the whites. 

 Furthermore, the brown shrimp appear less 

 well adapted to survive the high temperatures 

 of midsumnner in areas at the edges of the 

 bays. The postlarval white shrimp, however, 

 appear to do less well at low temperatures. 

 White shrimp apparently grow better at tem- 

 peratures above 77° F. At late spring and 

 summer temperatures, both species tolerate 

 a wide range of salinities--a factor which 

 may fluctuate in the bays during all seasons. 



Possible chemical differences between the 

 two species are also being studied, for we 



42 



