FISHERY BULLETIN: VOL. 78, NO. 3 



Table 2. — Analysis of variance of the effects of size, salinity, 

 temperature, and period on the mean oxygen consumption rates 

 ofPenaeus aztecus. 



Table 4.- 



-Mean oxygen consumption rates of Penaeus aztecus 

 for each test temperature; m = mass. 



Source of variation 



df 



Mean square' 



'• = P<0.05;"P<0.01. 



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



Table 3. — Mean oxygen consumption rates ofPenaeus aztecus 

 for the salinity-size interactions; m = mass. 



The average oxygen consumption rate increased 

 significantly with increasing temperature, from 

 0.29 mg 02-g wet m^i h'' at 18° C to 0.55 mg 

 Oag wet m-i-h-i at 33° C (Table 4). At each 

 salinity oxygen consumption increased linearly 

 with temperature, except at 30%o, where oxygen 

 consumption peaked at 28° C and decreased signi- 

 ficantly at 33° C (Figure 1, Table 2). 



Oxygen consumption rates differed significant- 

 ly among periods (Table 2). Rates during the first 

 15-min period averaged 0.44 mg O2 g wet m'^ h"^ 

 and decreased to an average of 0.40 mg O2 -g wet 

 m~i h"^ during the fourth 15-min period (Table 

 5). Significant differences of oxygen consumption 



Table 5. — Mean oxygen consumption rate of Penaeus aztecus 

 during four consecutive 15-min periods after 1 h acclimation in 

 respirometer chamber; m = mass. 



rates among period interactions were not found 

 (Table 2). 



When hemolymph osmolality was analyzed for 

 shrimp acclimated to the same conditions as previ- 

 ously described, size and salinity were significant 

 main effects; and salinity-size, temperature-size, 

 and salinity-temperature effects were signifi- 

 cant interactions (Figure 2, Table 6). The mean 

 hemolymph osmolality of 3.7 g shrimp was sig- 

 nificantly higher than that of 6.7 g shrimp (Tables 

 6, 7), but this difference was found only in combi- 

 nations that included 30%o S or 33° C. In 30%o S the 

 smaller shrimp's hemolymph osmolality averaged 

 over all temperatures was 796 mOsm (millios- 

 moles) compared with 753 for the larger shrimp. 

 At 33° C the same comparison averaged over all 

 salinities was 734 and 678 mOsm (Figure 2). 



The mean hemolymph osmolality increased 

 with increasing salinity (616, 696, and 774 mOsm 

 at 10, 20, and 30%o, respectively; Table 7). At each 

 salinity, the effect of increasing temperature on 

 the shrimp's hemolymph osmolality was tested. 

 Significant linear responses were obtained at 10 

 and 30%o (Table 6, Figure 3). Significant correla- 

 tions were not found between hemolymph osmolal- 

 ity and oxygen consumption rates. 



DISCUSSION 



Sources of Variability 



Many complicating variables must be consid- 

 ered in attempting to obtain the standard 

 metabolism of penaeid shrimp. Physiological 

 rhythms, stage of the molt cycle, and lunar phases 



746 



