FISHERY BULLETIN: VOL. 78, NO. 3 



Table 6. — Analysis of variance of the effects of size, salinity, 

 and temperature on the osmolality of Penaeus aztecus 

 hemolymph. 



'- = P<0.05;-- =P<0.01 

 ^Subscripts: I = linear; q = quadratic; c 



cubic. 



Table 7. — Mean hemolymph osmolality of Penaeus aztecus in 

 relation to size and salinity of acclimation water. 



850 



800 



S 750 



o 



E 



S 700 



>- 

 — I 



o 



5 



LU 



X 650 



600 



550 



S=10%o 



23 28 



TEMPERATURE (X] 



33 



Figure 3. — Mean hemolymph osmolality ofPenaeus aztecus vs. 

 temperature at salinities of 10, 20, and 30%o. 



Although no significant time-of-day differences 

 were found (Table 1), efforts were made to test 

 equal numbers of shrimp in the morning and af- 

 ternoon at each treatment combination. Evidence 

 indicates that shrimp are influenced by lunar cy- 

 cles (Wheeler 1937; Racek 1959; Aaron and Msby 

 1964; Wickham 1967; Hughes 1972; Bishop and 

 Herrnkind 1976), but in the present studies, we 

 assumed that lunar influences on the oxygen con- 

 sumption were negligible because of acclimation 

 periods. Subrahmanyam (1976) obtained results 

 indicating the presence of an oxygen consumption 

 rhythm in pink shrimp that coincided with the 

 tidal cycle, but this rhythm waned after the 

 shrimp were maintained for a week in captivity. 



Because of the absence of standardized 

 techniques for measuring routine oxygen con- 

 sumption of poikilotherms, many of the previous 

 studies on the oxygen consumption of penaeid 

 shrimp are of limited usefulness. Frequently per- 

 tinent circumstances relating to acclimation time 

 and (or) test conditions were not reported (Sub- 

 rahmanyam 1962; Zein-Eldin and Klima 1965; 

 Weerasinghe and Arudpragasam 1967; Steed and 

 Copeland 1967), and closed chambers were used in 

 most published studies. Consequently, test ani- 

 mals could not acclimate to test chamber condi- 

 tions and probably exhibited increased activity. 



In our studies, the shrimp's activity was 

 minimized by several methods: first, the test ani- 

 mals were acclimated to a specific test salinity- 

 temperature combination for at least a week prior 

 to testing; second, the shrimp were allowed to ac- 

 climate to the test chamber for an hour before data 

 were collected; and third, an inverted opaque plas- 

 tic bucket was placed over the test chamber to 

 reduce the light and to prevent disturbances from 

 human activity in the laboratory. 



Reducing the light to the test chamber reduced 

 the mean oxygen consumption (0.25 vs. 0.17 mg 

 02g wet m~' h"') although the effect was not 

 statistically significant. The hour acclimation 

 prior to taking data was not enough time to allow 

 the shrimp to adjust to the test chamber because 

 the oxygen consumption rate for each 15-min 

 period continued to decline throughout the second 

 hour (Tables 2, 5). Although the average oxygen 

 consumption rate decreased significantly during 

 each subsequent 15-min period of the second hour 

 of testing, the overall rate change was small, an 

 11% decrease between the first and last period. The 

 rate change was consistent across all treatments 

 and unrelated to the treatment effects because no 



748 



