FISHERY BULLETIN: VOL. 71, NO. 1 



after which the meat and shell matrix were re- 

 moved, rinsed with distilled water, blotted, and 

 dried. The majority of organisms and molluscs 

 meats were dried in a lyophilizer and ground to 

 pass through a 40-mesh sieve. Samples collected 

 during 1968 were dried at 60°C in an oven; no 

 attempt was made to compare the results of 

 caloric measurements on freeze-dried and oven- 

 dried samples. 



Caloric determinations were made with a 

 Phillipson type oxygen microbomb calorimeter 

 (Gentry Wiegert Instruments) .' Three to eight 

 pellet replicates, weighing from 5 to 25 mg dry 

 weight each, were run for each sample. After 

 each combustion a nitric acid determination and 

 correction was made (Parr Instrument Co., 

 1960). In addition, sulfur content of each sam- 

 ple was determined (American Public Health 

 Association, 1965) and a sulfur correction was 

 made on each replicate. Subsamples of each 

 material were ashed in a muffle furnace at 500°C 

 for 36 hr. Caloric content on a dry weight and 

 an ash-free dry weight basis were calculated 

 according to the Parr Manual (Parr Instrument 

 Co., 1960) and Phillipson (1964). 



RESULTS AND DISCUSSION 



We combusted 425 pellets of 93 samples repre- 

 senting 51 species-populations collected from the 

 estuarine system near Beaufort. The values we 

 obtained for ash content, percent dry weight, 

 and caloric content based on dry weight, ash- 

 free dry weight, and live weight are presented 

 in Appendix Table 1. Some general conclusions 

 have emerged from calorimetric studies, with 

 which our data agree, but specific values and 

 relations for an estuarine system have not been 

 presented before. 



We observed a statistically significant rela- 

 tion between energy content per gram dry weight 

 and the percent of organic matter in the sample 

 (r = 0.857; d.f. = 91) (Figure 1). The least 

 squares regression equation was 



y = 0.0604X — 0.420, 



where Y is kilocalorie per gram dry weight and 

 X is the percent organic matter (ash-free dry 

 weight) in the sample. This equation is similar 

 to those obtained by chemical comi30sition tech- 

 niques (Ostaypenya and Sergeev, 1963) for ma- 

 rine and freshwater organisms: 



Y = 0.0616Z 



0.286 



and for marine crustaceans and molluscs: 



Y = 0.0617X 



0.581. 



The similarity of the three regression equa- 

 tions suggests a general relation between the 

 caloric content and the percent dry matter of all 

 aquatic organisms. We are continuing to col- 

 lect and analyze samples, however, to determine 

 whether there are seasonal differences. 



The linear regression suggests that if there 

 are changes in chemical composition of the or- 

 ganic matter, primarily differences in the per- 

 cent lipid material, they are obscured in this 

 relation by relatively large amounts of inorganic 

 substances in the dry tissues of the organisms. 

 We therefore analyzed the correlation between 

 energy content per gram organic matter and the 

 percent organic matter in the samples. Where 

 applicable, corrections for endothermy (Paine, 

 1964, 1966) were applied. The resulting cor- 

 relation, although significant, was low (r = 

 0.333; d.f. = 91) indicating great scatter about 

 the regression line. The least squares regression 

 equation was: 



K 



0.0183X + 3.991, 



* Reference to trade names in the publication does not 

 imply endorsement of commercial products by the Na- 

 tional Marine Fisheries Service. NOAA. 



where K is kilocalorie per gram organic mat- 

 ter and X is the percent organic matter. The 

 slope of this line is significantly greater than 

 zero, indicating that the organic matter of the 

 species tested did not have a constant propor- 

 tion of lipid, protein, and carbohydrate materials. 

 These chemical differences were not obvious 

 from the regression analysis of energy per gram 

 dry weight because they were masked by inor- 

 ganic substances. 



It is possible that acid digestion of molluscs 

 may have altered their caloric content. Paine 



290 



