CONDREY, GOSSELINK. and BENNETT: SHRIMP DIETS 



ilar in organic content but differing in ash con- 

 centration. 



NET ASSIMILATION RATE 



Where either the ingestion or egestion rate is 

 determined, Equation 2 can be readily adapted 

 to yield the net assimilation rate. For the latter 

 case, the organic weight egested (N) is defined 

 as the product of the ratio of organic matter 

 to dry weight egested (£") and dry weight eges- 

 ted (E). Net assimilation, in terms of egested 

 material, is 



/, = rj = r,{FF'), 



(6) 



A = 



(E)(E')(U') 

 (100 — U') 



(4) 



where (100 — U') is the percentage of ingested 

 organic food that is egested. When E is reported 

 in terms of dry weight of feces deposited per 

 unit time. Equation 4 yields the rate at which 

 net assimilation of organic matter proceeds. 



ASSIMILATION PARAMETERS FOR 

 SPECIFIC ORGANIC MOIETIES 



NET ASSIMILATION AND FEEDING 

 EFFICIENCIES OF AN ORGANIC MOIETY 



The determination of the net assimilation 

 efficiency of an organic moiety (U'x) indepen- 

 dent of U' is not possible by direct substitution 

 in Conover's equation (Equation 2). This be- 

 comes clear if one considers the equation for net 

 assimilation efficiency of a specific organic 

 moiety. 



t/'. 



/x — N. 



X 100 



(5) 



where h is the amount of the moiety ingested 

 and Nx the amount of the moiety egested. Con- 

 over was able to derive Equation 2 from Equa- 

 tion 1 by setting / equal to total particulate mat- 

 ter egested minus its ash. Clearly this relation- 

 ship does not hold for Ix and Nx in Equation 5. 

 Let n and r„ be ratios of the weight of the 

 organic moiety of interest to the total organic 

 weight of the food and feces respectively. Then 



and 



Nx = TnN = rniFF'){l — t/7100). (7) 



Substituting in Equation 5: 



U'x 



n — r„ (1 — 177100) 



n 



X 100. (8) 



From Equations 6 and 7 the feeding efficiency of 

 an organic moiety is: 



Ax/F = F' [n — r„ (1 — U'/lOO)]. (9) 



NET ASSIMILATION RATE OF 

 AN ORGANIC MOIETY 



The amount of a particular organic moiety 

 egested can be defined as 



Nx = {E)iE'){r„). 



(10) 



Similarly, 



/x = 



(E) (E') (^n) 



(1_[7V100) 



(11) 



When E is defined as the amount of feces de- 

 posited per unit time, Equations 10 and 11 be- 

 come rate equations for determining the amount 

 of a moiety ingested and egested per unit time. 

 The assimilation rate of the moiety is the dif- 

 ference between the values of Ix and Nx. 



EXPERIMENTAL TECHNIQUES 



FEEDING 



Juvenile shrimp, Penaeus setiferus and P. 

 aztecus, 24 to 83 mm long, were collected from 

 Barataria Bay, La., and maintained in aerated 

 aquaria containing acid-washed quartz sand, 

 filled with membrane-filtered bay water at 20°- 

 23°C. 



Test foods were given to shrimp which had 

 been starved for 12 hr, in groups of 10 to 14, 

 unless otherwise noted. Animals were allowed 

 to feed ad lib. for 12 to 36 hr. Fecal material 



1283 



