CONDREV, GOSSELINK, and BENNETT: SHRIMP DIETS 



The primary question raised by Forster and 

 Gabbott for our results is the reliability of Con- 

 over's ratio method. They were unable to ac- 

 count for 29 to 40 Cr of the ash, and were not 

 certain whether this was assimilated or lost to 

 solution. With the ratio method assimilation of 

 ash leads to underestimation of assimilation ef- 

 ficiency. For such a case the corrected assimila- 

 tion efficiency ( C/'correct) is given by the equation: 



t/'correct = U'/lOO + (An/A,) 



IE'(1—F')/F'il—E')] X 100 



where A„/Af is the fraction of ash assimilated. 

 Similarly for U'x the corrected value is found 

 by the same equation except that the second term 

 is also multiplied by Vn/ru From these equations 

 it can be seen that the error incurred by failure 

 to correct for assimilation of ash varies inversely 

 with the ash content of the food and directly with 

 the organic content of the feces. Thus errors are 

 magnified when U' is low. If we assume that the 

 upper limit of ash assimilation reported by 

 Forster and Gabbott applied to our studies, the 

 error in our U' values would be less than 10% 

 for all diets except AF-1, which would have been 

 in error by 35%. Similarly, high U'x values 

 would have small errors, low values relatively 

 large errors. 



We consider it likely that the high apparent 

 ash assimilation of Forster and Gabbott are re- 

 lated to the organism used and the experimental 

 conditions. They point out that loss of ash may 

 have occurred through regurgitation and excre- 

 tion. These parameters would be important 

 when shrimp are fed for a short period (15 min) 

 and feces collected subsequently over a long pe- 

 riod (20 hr). On the other hand in our tests 

 we observed no regurgitation, the shrimp fed 

 continuously, and feces were collected about 

 every 2 hr. These conditions should minimize 

 ash loss. 



ACKNOWLEDGMENTS 



This study was supported by funds from the 

 National Oceanic and Atmospheric Administra- 



tion through the Louisiana State University 

 (LSU) Ofl^ce of Sea Grant Development. We are 

 indebted to the encouragement and assistance 

 of the many members of the LSU faculty. In 

 particular, we wish to thank Dr. Samuel P. 

 Meyers and Dennis Butler, Department of Food 

 Science, LSU, for providing the formulated diets 

 and assisting in pelletizing the foods. We are 

 indebted to Dr. S. P. Meyers and Drs. R. Collins 

 and J. P. Woodring, Department of Zoology, 

 LSU, for their criticism of the test. The senior 

 author wishes to thank Jerry Broom and the 

 staff" of the Grande Terre Laboratory of the 

 Louisiana Wildlife and Fisheries Commission 

 for their aid and advice. It is a pleasure to 

 acknowledge the excellent technical assistance 

 of Kathy LeBlanc and Linda Lambert. 



LITERATURE CITED 



CONDREY, R. E. 



1971. Comparative assimilation efficiencies of pen- 

 aeids fed on natural and artificial diets. MS 

 Thesis, Louisiana State Univ., Baton Rouge, 

 45 p. 



COXOVER, R. J. 



1966a. Assimilation of organic matter by zooplank- 

 ton. Limnol. Oceanogr. 11:338-345. 



1966b. Factors affecting the assimilation of or- 

 ganic matter by zooplankton and the question of 

 superfluous feeding. Limnol. Oceanogr. 11:346- 

 354. 

 Corner, E. D. S., .and C. B. Covvey. 



1968. Biochemical studies on the production of ma- 

 rine zooplankton. Biol. Rev. (Camb.) 43:393- 

 426. 

 Corner, E. D. S., C. B. Cowey, and S. M. Marshall. 



1967. On the nutrition and metabolism of zooplank- 

 ton. V. Feeding efficiency of Calanus finmarchi- 

 ciis. J. Mar. Biol. Assoc. U.K. 47:259-270. 

 Ball, W. 



1965. Studies on the physiology of a shrimp, 

 Metapenaeiis sp. (Crustacea: Decapoda: Penae- 

 idae). IV. Carbohydrate metabolism. Aust. J. 

 Mar. Freshwater Res. 16:163-180. 



1967. The functional anatomy of the digestive tract 

 of a shrimp Metapenaeus bennettae Racek & Ball 

 (Crustacea: Becapoda: Penaeidae). Aust. J. 

 Zool. 15:699-714. 



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