BISHOF ET AL. OXYGEN CONSUMPTION OF BROWN SHRIMP 



A closed, continuously flowing, differential res- 

 pirometer was used to measure the oxygen con- 

 sumption rates. Its basic design was modified from 

 the apparatus employed by Keys (1930) and con- 

 sisted of a test chamber positioned between two 

 oxygen polarographs through which a known vol- 

 ume of water flowed from a supply to a catchment 

 reservoir (Bishop 1976). Hourly flow rates varied 

 between 1.934 and 2.519 1 depending on salinity- 

 temperature combinations. 



Prior to a test, polarograph readings were 

 checked for identical response, shrimp were placed 

 in the chamber, the chamber voided of air and 

 sealed, and the water switched to flow through the 

 test chamber. At the end of a test, water flow was 

 again shunted past the chamber, and probe read- 

 ings were rechecked to ensure similar readings. 

 Probes were read to the nearest 0.05 ppm. If probe 

 drift occurred and exceeded 0.15 ppm the test was 

 discontinued and disregarded. If drift occurred, 

 but was <0.15 ppm, it was assumed to have oc- 

 curred at a constant rate, and data were corrected 

 accordingly. After a test the shrimp were mea- 

 sured, sexed, and weighed individually. Except for 

 diurnal experiments, all tests lasted 2 h. Mean live 

 mass (m ) of test shrimp is used to denote the size 

 class of shrimp being discussed. Hourly rates of 

 oxygen consumption are expressed on a per 

 gram live mass basis, i.e., mg O^ -g wet m~' h'K 

 Statistical designs and arrangements were from 

 Cochran and Cox (1957) and Steel and Torrie 

 (1960), and significant differences were tested at a 

 = 0.05 or 0.01. 



Experiments 



Diurnal Effects 



Light; Reduced-Light Effects 



Four 6.7 g shrimp were individually tested 

 while exposed to laboratory light ( 193 Im m"^ ). Test 

 salinity and temperature were 20%o and 25° C, and 

 tests lasted 2 h. An inverted, bottomless, opaque 

 plastic bucket was placed over the test chamber to 

 preclude visual disturbances. The next day each 

 shrimp was again tested in the same sequence, but 

 the light was reduced ( <10 Im m") by placing an 

 intact plastic bucket over the test chamber. Two 

 days of similar tests were repeated with three dif- 

 ferent 6.7 g shrimp except that the shrimp were 

 first tested in reduced light. An ANOVA in a cross- 

 over design was computed on the average oxygen 

 consumption rates of the last two 15-min periods. 



Disturbance Effects 



Four 6.7 g shrimp were tested singly for oxygen 

 consumption after disturbance. Test salinity and 

 temperature were 20%o and 25° C, and ambient 

 oxygen concentration was 7.4 ppm. Shrimp were 

 placed in the test chamber, and the chamber was 

 shaken by hand for approximately 5 min. The 

 highest oxygen consumption rate during the fol- 

 lowing 15 min was considered to approach that for 

 active shrimp. 



The lowest oxygen consumption rate of shrimp 

 from four randomly selected diurnal experiments 

 was obtained to estimate standard respiration. 

 Because both disturbance and diurnal tests were 

 conducted at the same salinity and temperature, 

 oxygen consumption differences between these 

 two test conditions should result primarily from 

 increased metabolic activity. We used f-tests com- 

 paring two sample means to test for significant 

 differences between the shrimp's resting and ac- 

 tive oxygen consumption rates. 



Five 6.7 g shrimp were tested individually for 24 

 h under a 12:12 LD photoperiod. Test salinity and 

 temperature was 20%o and 25° C, respectively. 

 Shrimp were allowed to acclimate to the test 

 chamber during the first 1.5 h. Except for the ini- 

 tial 1.5 h and 1 h following each probe check, oxy- 

 gen consumption data were averaged for each 

 15-min period and grouped into eight 3-h intervals 

 (0630-0930, 0930-1230, ..., 0330-0630 h). An 

 analysis of variance (ANOVA) employing a ran- 

 domized block design was computed on the aver- 

 age oxygen consumption for each shrimp (block) 

 during the eight 3-h intervals (treatments). 



Crowding Effects 



The effects of crowding on the oxygen consump- 

 tion of 3.7 and 6.7 g shrimp were investigated. 

 Area of the test-chamber floor was 103.9 cm^, and 

 chamber volume was 240 ml. Shrimp were tested 

 at 20%o S (salinity ) and 25° C. Light was reduced to 

 <10 Im m~2 during the tests by placing an in- 

 verted, opaque plastic bucket over the test 

 chamber. Eight replicates were obtained for 3.7 g 

 shrimp tested in groups of one and two, and a ^-test 

 involving two sample means was employed to test 

 for significant differences. Eight replicates of 6.7 g 



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