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20. ABSTRACT (Continued). 



and temperatures were 18°, 25° and 32°C. The duration of the tests was for one 

 week (168 hours). The behavior of the experimental shrimp was influenced at 

 25°C, which was their normal habitat temperature, primarily by salinity changes. 

 At other temperatures the behavior was affected by the interaction of salinity 

 and temperature. The blood osmotic and chloride ion regulation was hyperos- 

 motic below and hyposmotic above the control salinity level. The rate of sa- 

 linity adaptation was determined on the basis of steady-state levels in oxygen 

 uptake and in blood osmotic or chloride concentration levels. At 25°C there 

 was a positive interaction in the various phases of adaptation between the res- 

 piratory rates on the one hand and the osmotic and chloride ion gradients on 

 the other hand in the respective salinities. This interaction was not consis- 

 tent at other test temperatures. On the basis of osmotic and chloride ion 

 steady-state levels, salinity adaptation was faster at 25°C than at either 18° 

 or 32°C; also salinity adaptation occurred in a wider range of 2 to 36°/oc>S 

 within a week. The salinity range of adaptation decreased from 5 to 25°/oo at 

 18°C and from 10 to 25°/ooS at 32°C. Within those salinity ranges the rate of 

 mortality was usually low. Next to 25°C the salinity adaptation and survival 

 rates were more favorable in 18°C than in 32°C. However, at 18° and 32°C the 

 steady-state levels in the respiratory rates and in the blood osmotic (or 

 chloride ion) concentrations appeared at different periods after the transfer 

 was made. Consequently there was no synchrony between these responses at 18° 

 or 32°C as opposed to 25°C test conditions. The respiratory rates at 18°C 

 reached steady-state levels faster than the osmotic or chloride ion concentra- 

 tions. On the contrary, at 32°C the steady-state levels appeared in the blood 

 salt levels faster than in the respiratory rates. These discrepancies might 

 have occurred partly due to the temperature-related differences in the be- 

 havioral pattern of shrimp. Normally the shrimp exhibited prolonged hyper- 

 activity at 32°C and inactivity at 18°C which naturally influenced the 

 respiratory rates both quantitatively and in relation to the time scale. In 

 this report the implications of deriving conclusions on the state of salinity 

 or temperature adaptation by taking individual physiological responses (i.e. 

 respiratory rates) as an exclusive criterion are discussed. In brown shrimp, 

 salinity and temperature requirements are shown to be size-dependent. The 

 optima for subadult shrimp (95 mm mean length) seem to exist above 10°/ooS, 

 preferably between 15 and 25°/ooS, and below 25°C. In contrast the juveniles 

 (70 mm mean length) of our previous studies have shown preference to salini- 

 ties lower than 17°/oo and to temperatures slightly higher than 26°C. The 

 possible existence of seasonal salinity and temperature optimal rhythms is 

 discussed in relation to the life cycle of brown shrimp. Magnesium, calcium 

 and potassium levels of the blood increased with salinity increases. Changes 

 in test temperatures (18° or 32°C) affected the normal regulation pattern of 

 these ions exhibited at 25°C. The physiological or behavioral responses were 

 not significantly affected when minor changes occurred in these ionic ratios. 

 Major changes, however, produced some physical abnormalities and high death 

 rates. The effects became greater at temperatures higher than 18°C. Below 

 35 percent of the normal calcium levels the shrimp started dying; death rates 

 increased with decreased calcium and increased temperature. Complete removal 

 of magnesium from the test salinity was relatively less harmful than the re- 

 duced calcium levels. Reduced potassium killed even fewer shrimp, but pro- 

 duced a high incidence of abdominal (tail) cramps in shrimp. Low blood 

 potassium levels and low temperature combinations seemed to cause the cramping 

 in shrimp. 



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