FISHERY BULLETIN: VOL. 70, NO. 4 



vealed that in the foods 75 to 85% of organic 

 weight was accounted for. These results were 

 consistent, indicating the presence of organic 

 components which are not detected by any of 

 the three methods. Recovery of organic frac- 

 tions from fecal material was, with the excep- 

 tion of the detritus diet, lower than with foods, 

 ranging from 60 to 749 of organic weight of 

 the feces. The implication is that the unaccount- 

 ed organic components of the food are also poorly 

 assimilated by shrimp and accumulate in the 

 feces. We have not been able to identify the 

 chemical nature of these components. 



DEFINED DIETS 



Net Assimilation Efficiency of Total Organic 

 "Weight and of Organic Moieties 



Tables 2 and 3 show results of chemical anal- 

 yses of the defined diets and of the feces of 

 shrimp fed on these diets. Data are presented 

 not as amounts, but as percentages for incor- 

 poration into the ratio equations. 



Assimilation efficiencies calculated from these 

 data (Table 4) revealed that the organic matter 

 of three of the diets was assimilated with a high 

 degree of efficiency. These diets were the diatom, 

 87 9f; the detritus, 85 S^; and the Chow, 80 Sr. 

 The similarity in overall digestibility suggests 

 an adaptive trituration and enzymatic apparatus 

 operating as efficiently against diatom frustules 

 as against bacterial cell walls. The ability to 

 assimilate effectively varied diets of animal, 

 vascular plant, and algal origin denotes the true 

 omnivorous habit of the shrimp. 



Table 4. — Net assimilation efficiencies of total organic 

 matter, protein, lipids, and carbohydrates for shrimp fed 

 on defined diets. 



Dieti 



Total 



organic wt 



U' 



Proteins 

 V' 



Lipids 

 U', 



Carbohydrates 

 ^'CH.0 



1 Diatom and Chow diets were fed to white shrimp, and detritus and 

 AF-1 diets were fed to white and brown shrimp. 



Although the two artificial diets were com- 

 parable in chemical analyses, the overall digest- 

 ibility of AF-1 (55*^^^ ) was low compared with 

 the Chow. According to Brazka (in Edmondson 

 and Winberg, 1971) , this indicates either a "spe- 

 cific barrier" in digestion of the diet or super- 

 fluous feeding. Of the components of AF-1, the 

 shrimp meal, because of its high chitin content, 

 may be the cause of the inefficiency of assimila- 

 tion. 



In general, lipids and proteins were digested 

 with a higher efficiency than total organic assim- 

 ilation while carbohydrate assimilation lagged. 

 The main exception to these generalizations was 

 the detritus protein, which was assimilated with 

 an efficiency of 75 9f compared to 85 9f for U'. 

 Bacterial cell walls reportedly account for from 

 10 to 40 "^r of the dry weight of the cells and are 

 composed of as much as 75 "^r protein (Pelczar 

 and Reid, 1965). The lower digestibility of 

 detritus protein may be due to an enzymatic 

 inability to attack the compacted cell wall pro- 

 tein. However, the results for this diet are not 

 clear since the assimilation efficiencies for the 

 specific organic moieties are all equal to or lower 

 than U'. This implies either that (1) the cor- 

 rection factors and standards employed were not 

 representative of the organic moieties present 

 in the samples or that (2) an unmeasured frac- 

 tion of the total organic weight was assimilated 

 with a higher efficiency than the total organic 

 matter. These difficulties are inherent in any 

 general analysis of this type and indicate the 

 necessity for care in interpretation of results. 



For protein digestibility our results are con- 

 siderably higher than those of Nose (1964), 

 who used a chromium oxide tracer to study as- 

 similation of protein by Penaens japoniciis. On 

 a diatom diet he found a U'p of 62.5 ''r ; on Ulva, 

 a green alga, a maximum of 30 '^r. The experi- 

 ments are difficult to compare with ours because 

 Nose also found a direct proportionality between 

 nitrogen content of the diet and U'p. Assimila- 

 tion efficiency of protein increased with diet 

 nitrogen. His diatom and Ulva diets were 1.36 

 and 1.649^ nitrogen, respectively, compared to 

 our analyses of 7.6*^^ in Cylindrotheca fusifor- 

 mis. At the diet nitrogen concentration we mea- 

 sured one would expect, using the proportional- 



1286 



