FISHERY BULLETIN: VOL. 78, NO. 3 



shrimp in groups of one, two, and three, and four 

 replicates of 6.7 g shrimp in groups of four were 

 also tested. An ANOVA in a completely ran- 

 domized design was computed for the average oxy- 

 gen consumption of the last two 15-min periods of 

 each test. 



Size, Salinity, and Temperature Effects 



The influence of salinity and temperature was 

 tested on the oxygen consumption and osmoregu- 

 lation of two sizes of P. aztecus. Three test 

 salinities (10, 20, 30%o) and four temperatures ( 18°, 

 23°, 28°, 33° C) were selected to represent ranges 

 that shrimp may experience in estuaries. 



Shrimp were caught and maintained in 

 salinities approximating 20%o; after acclimation 

 to room temperature (23°-25° C) in the laboratory, 

 shrimp of each size class were distributed equally 

 among tanks of 10, 20, and 30%o S. Transferred 

 shrimp experienced no difficulties adjusting to a 

 10%o S change at 23°-25° C. Ambient laboratory 

 temperature was lowered to 18° C and maintained 

 for a week. After oxygen consumption or hemo- 

 lymph data were obtained from acclimated 

 shrimp, ambient temperature was gradually 

 raised for the next test and the procedure re- 

 peated. Four to five days appeared to be necessary 

 to raise the temperature from 28° to 33° C; shrimp 

 mortality increased with faster acclimation rates. 



Shrimp were tested in pairs because two shrimp 

 of the smaller size were necessary to cause approx- 

 imately a 1 ppm oxygen concentration dif- 

 ference between the probes at the tested flow 

 rates. A 1 ppm difference minimized percent- 

 age error caused by translating data from the 

 strip-chart recorder and permitted enough flow 

 through the test chamber to avoid oxygen deple- 

 tion and excreta buildup. An inverted plastic 

 bucket was placed over the chamber during tests 

 to preclude visual disturbances and to reduce light 

 (<10 1mm-2). 



Each of the 24 treatment combinations (2 sizes 

 X 3 salinities x 4 temperatures) was replicated 

 seven or eight times, and each test lasted 2 h. 

 Acclimated shrimp were selected completely at 

 random without replacement for each test. There- 

 fore the oxygen consumption of a minimum of 

 seven pairs of different shrimp was obtained for 

 each treatment combination. To allow shrimp 

 time to acclimate to the test chamber, data ob- 

 tained during the first hour were disregarded. 

 Data collected during the second hour were divid- 



ed into four 15-min periods and the average oxygen 

 consumption for each period was calculated. An 

 ANOVA employing a split plot in a completely 

 randomized design with a 2 x 3 x 4 factorial 

 arrangement as the whole plots and period as the 

 subfactor was computed on the data. The effects of 

 the treatments (size, salinity, temperature), the 

 periods, and the interactions on the oxygen con- 

 sumption rates were evaluated. If a significant 

 difference was found, then orthogonal compari- 

 sons (Snedecor and Cochran 1967) were made to 

 explain more specifically the differences among 

 the treatments, periods, and their interactions. 

 Data plotted in the graphs are the average oxygen 

 consumption during the last Va h (the third and 

 fourth periods) only. 



Shrimp for the osmoregulation studies were 

 caught between 20 March and 20 April 1974 at 

 Airplane Lake. After shrimp were acclimated in 

 the laboratory, hemolymph samples were obtained 

 by puncturing the dorsal arthroidal membrane 

 (just anterior to the first abdominal segment) and 

 bleeding no less than 0.2 ml directly into cuvettes. 

 Cuvettes were sealed with Parafilm to prevent 

 evaporation. The least amount of hemolymph 

 necessary for accurate osmolality determination 

 was 0.2 ml and was obtained from each 6.7 g 

 shrimp; however, two 3.7 g shrimp were needed to 

 collect the minimum volume. Osmolality was 

 measured within 1.5 h with an Osmette. Five sam- 

 ples were tested for each treatment combination 

 except for the following instances: 6.7 g shrimp at 

 18° C and 10%o S— three samples; 3.7 g shrimp at 

 33° C and 10, 20, 30%o S— four samples; and 6.7 g 

 shrimp at 18° and 28° C and 30%o S— four samples. 

 Hemolymph was not centrifuged, and little diffi- 

 culty was experienced in obtaining repeatable 

 readings with the Osmette. 



Data were analyzed by an ANOVA employing a 

 2x3x4 factorial arrangement in a completely 

 randomized design, and orthogonal comparisons 

 were made on treatment combinations with sig- 

 nificant differences. Correlations between 

 hemolymph concentration and oxygen consump- 

 tion data at corresponding size, salinity, and 

 temperature combinations were made. 



RESULTS 



Diurnal Effects 



Mean oxygen consumption rates ranged from 

 0.18 to 0.30 mgOag wet m~^ h"^ among the eight 



744 



