BISHOP ET AI,.: OXYGEN CONSUMPTION OF BROWN SHRIMP 



4,686, or 4,500 cal, respectively (Giese 1968). The 

 caloric value of each of these sources varies <67( 

 from the mean. Therefore, for every milligram of 

 oxygen consumed, about 3.31 cal will be liberated. 

 A 6.7 gP. aztecus utilizes 0.87 and 3.75 mg 0^ h'^ at 

 rest and during activity at 25° C, which translates 

 to 2.88 and 12.41 cal h"V (The caloric expenditure 

 during activity is calculated from the maximum 

 oxygen consumption over a 15-min period.) Other 

 average energy expenditures of P. aztecus at 

 selected conditions are presented in Table 11. 



T.\BLE 11. — Mean rates of oxygen consumption and energy ex- 

 penditures ofPenaeus aztecus at each test temperature averaged 

 over all test salinities; m = mass. 



Q 



About 80% of a penaeid shrimp's mass is water, 

 so the dry mass of a 3.7 and a 6.7 g shrimp ap- 

 proaches 0.74 and 1.34 g, respectively. A gram of 

 dried whole Metapenaeus monoceros yields 3,066 

 cal upon combustion (Qasim and Easterson 1974); 

 thus the energy content of a 3.7 g P. aztecus is 

 about 2,269 cal and that of a 6.7 g shrimp, about 

 4,108. 



If a 6.7 g shrimp maintains a resting state for 24 

 h at 25° C, then a minimum of 69 cal will be 

 utilized just for maintenance. This is about 1.7'7f of 

 its total caloric content or 0.11 g wet mass equiva- 

 lent. Therefore, a 6.7 g shrimp must daily assimi- 

 late a minimum of 1.7*7^ of its body wet mass of 

 equal caloric value food to maintain itself at rest. 

 If a maximum state of activity were continued for 

 24 h (oxygen consumption = 0.56 mg Og g wet 

 m"'h"', then approximately 298 cal would be 

 expended. This is more than 7.27c of the 6.7 g 

 shrimp's total caloric content. Shrimp obviously do 

 not maintain a continuous state of maximum ac- 

 tivity, and their mean daily energy expenditure is 

 probably 3-4% of body caloric content. 



Oxygen consumption averaged over all test 

 salinities and at 23° and 28° C during the fourth 

 15-min test period was 0.40 and 0.37 mg O2 g wet 



*H. C. Loesch, marine biologist, 1232 Dahlia St., Baton Rouge, 

 LA 70808, unpubl. data 13 November 1974. 



m'h' for 3.7 and 6.7 g shrimp (Bishop 1974). 

 These two shrimp sizes and water temperatures 

 are characteristic of Barataria Bay, La. during 

 May (St. Amant et al. 1966), and an average oxy- 

 gen consumption rate of 0.38 mg Ogg wet 

 m~ih~i should be a conservative estimate of 

 routine oxygen consumption for inshore shrimp 

 during this time period. Because P. aztecus buries 

 itself in the substrate during the day (Williams 

 1965), we calculated daily caloric expenditures 

 based on a routine state of metabolism for 12 h and 

 a resting state for 12 h. Using the average value of 

 0.38 mg O^g wet m~*h~^ for routine oxygen 

 consumption and 0.13 mg Og -g wet m~' h"! for 

 standard metabolism for 5.2 g P. aztecus (average 

 of 3.7 and 6.7 g shrimp), a daily caloric expendi- 

 ture of 105 cal is obtained. This is about 3.3% of a 

 5.2 g shrimp's caloric content and supports the 

 assumption of a 3-4% expenditure of their body 

 wet mass per 24 h. 



St. Amant et al. ( 1966) estimated that P. aztecus 

 grew an average of 1 mm d ' while in the es- 

 tuaries, which represents a daily gain in wet mass 

 of 0.18 g (Fontaine and Neal 1971) or 110 cal in 

 potential energy. 



Because shrimp feed on a variety of materials in 

 the estuary (Williams 1955; Dall 1968; George 

 1974), assimilation rates probably vary widely de- 

 pending on the food ingested and its chemical 

 composition. Assimilation efficiency calculated on 

 a mass basis may differ from that based on 

 calories, and a range of efficiencies would be ex- 

 pected in natural conditions. As assimilation effi- 

 ciency decreases, maintenance energy increases, 

 but the point of diminishing returns is not known. 

 Condrey et al. (1972) determined from laboratory 

 experiments that shrimp of the genus Penaeus 

 assimilated 33-74% of the ingested food mass, and 

 Jones (1973) reported 25-40% assimilation rates 

 from shrimp feeding naturally in Airplane Lake. 

 Using extremes of these percentages and assum- 

 ing that assimilation rates for mass and calories 

 are similar and ihaXP. aztecus is primarily a detri- 

 tal consumer in Louisiana estuaries, first order 

 approximations are possible for daily ingestion 

 rates (Table 12). 



Assimilation (A ) of food energy must equal the 

 sum of that for respiration {R), stored energy 

 (growth G), and excretion iE) (see Table 12). As- 

 similated food is derived from food ingested (/). If 

 the energy assimilation efficiency (A// x 100) is 

 assumed to be 34% , a 5.2 g shrimp must consume 

 about 638 cal d" at observed growth rates [G + 



753 



