were more favorable toward the high salinities (36 and 45°/ooS) than 

 the smaller ones (60 mm) and vice versa. O'Driscoll (1975 unpub- 

 lished data) found a narrower salinity tolerance range in adults of 

 140 mm mean length than in the adults of 110 mm mean length. 



The evidence indicates that wide salinity tolerance range is 

 important for the survival of the species when they are young; it 

 becomes narrower in later life. In young shrimp this ability pro- 

 motes a wider dispersal in the estuaries and bayous. In adults that 

 are about to emigrate offshore, tolerance to low salinities has no 

 obvious survival value. 



The shrimp (95 mm) in our present experiments were about to 

 emigrate to the open sea. As such, the size factor has another im- 

 plication concerning the temperature requirements. Offshore tem- 

 peratures are normally lower than the summer and fall temperatures 

 in coastal waters. It was shown in the earlier part of the discus- 

 sion that the shrimp acclimated to 18°C were faster in salinity 

 adaptation than those acclimated to 32°C if not at 25°C. In view 

 of the impending offshore emigration it is likely that the shrimp 

 are undergoing a sort of physiological preparation to meet the low 

 temperature and high-salinity conditions. Such preparation may 

 occur on a seasonal cyclic basis in brown shrimp. This possibility 

 was shown below on the basis of rates from an earlier study by 

 Venkataramiah et al. (1974). 



Prior to the experiments the juvenile brown shrimp (70 mm) 

 were acclimated to 8.5, 17.0, 25.5, and 34.0°/ooS and 21°, 26°, 

 and 31 °C combinations for more than three weeks. Then they were 

 tested in the same conditions as their acclimation. The respira- 

 tory rates were lower in low salinity (8.5 and 17.0°/oo) and warm 

 temperature (26° and 31°C) and high salinity (25.5 and 34.0°/oo) 

 and low temperature (21 °C) combinations than in others. The low 



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