COMPARISON OF THE ASSIMILATION OF DIFFERENT DIETS BY 

 PENAEUS SETIFERUS AND P. AZTECUS 



Richard E. Condrey,' James G. Gosselink^ and Harry J. Bennett= 



ABSTRACT 



Juvenile penaeid shrimp showed high and comparable assimilation- efficiencies (80-85%) 

 on a variety of plant and animal diets. In general assimilation efficiencies for proteins 

 and lipids were consistently high; for carbohydrates, low. Organic assimilation per 

 gram organic weight of white shrimp, Penaeus setiferus, proceeded at 3.7 mg hr~i on 

 an axenic diatom and 8.4 mg hr~i on an artificial diet. The assimilation efficiency was 

 lower for shrimp feeding on the algal mat coating Spartina alterniflora than on two 

 components of the mat. Feeding mechanisms and probable natural diets are discussed 

 as a basis for further study. 



In tidal estuaries where consumers are heavily 

 dependent on an input of autochthonous and al- 

 lochthonous detritus, the trophic structure is ob- 

 scured by the seemingly omnivorous habit of 

 many of the residents. Historically, the feeding 

 habits of these omnivores have been investigated 

 by examination of gut contents, correlation of 

 numbers of omnivores with type of benthic com- 

 munity, and comparison of the types of foods 

 available in different areas with the species com- 

 position of consumers (Darnell, 1964; Corner 

 and Cowey, 1968; Edmondson and Winberg, 

 1971 ) . While these investigations have been val- 

 uable and are the bases of our present under- 

 standing of estuarine communities, it should be 

 noted that a large percentage of the foregut con- 

 tents of many estuarine species is unidentifiable 

 (Darnell, 1964). 



In Louisiana estuaries shrimp is seasonally 

 one of the dominant organisms and commercially 

 the most important one. Although speculation 

 about the diet of juvenile shrimp in inland 

 waters has been widespread, the datum base in 

 the literature for these speculations is not con- 

 vincing. Studies of shrimp gut contents (Flint, 



' Louisiana State University, Baton Rouge, La. ; 

 present address: College of Fisheries, University of 

 Washington, Seattle, V^A 98195. 



- Louisiana State University, Baton Rouge, LA 70803. 



Manuscript accepted April 1972. 



FISHERY BULLETIN: VOL. 70, NO. 4, 1972. 



1956; Darnell, 1964) seem to indicate that the 

 organism ingests the dominant materials in the 

 sediments. In Lake Ponchartrain, for instance, 

 Darnell (1961) found that 58^/c of the stomach 

 contents of adult white shrimp was unidentifiable 

 detritus. Little is known, however, about the 

 ability of shrimp to digest difl'erent food sources. 

 Nose (1964), working with Penaeus japonicus, 

 reported a higher assimilation efficiency of ani- 

 mal than of plant proteins. Fujii et al, (1963) 

 and Dall (1965) have studied the activity of 

 digestive enzymes of several species of shrimp. 

 This study concerns the assimilation by the 

 white shrimp, Penaeus setiferus, and the brown 

 shrimp, P. aztecus, of the organic components 

 of four diflferent defined diets and a natural sub- 

 strate. Except for the rates reported, the as- 

 similation parameters were measured by a mod- 

 ification of the ratio method of Conover (1966a) . 

 Therefore, quantitative recovery of food or feces 

 was not required. 



METHODS AND MATERIALS 



CALCULATION OF ASSIMILATION 

 PARAMETERS OF ORGANIC MATERIAL 



Direct calculation of net assimilation is dif- 

 ficult in aquatic environments because of the 

 need to measure quantitatively both ingestion 



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