Boggs: Bioenergetics and growth of Engrauhs mordax 



559 



Evacuation of the food from the stomach was slow 

 (Fig. 3). The absence of an immediate decline in stom- 

 ach contents after feeding suggested a gastric pause 

 or coprophagy, although this result may be due to sam- 

 pling errors. The following regression (using a semilog 

 transformation) of mean stomach contents (Y in grams 

 food/gram fish) versus elapsed time (T in hours after 

 feeding stopped) describes the data from eight hourly 

 samples (Table 2, Fig. 3): 



log e Y = -2.995 - 0.106 T (N 8, r 2 0.81). (2) 



Taking the antilog 



Y = 0.05 e-°- 106 T g food / g fish, (3) 



the actual amount of food consumed (C T ) between the 

 initiation and cessation of feeding was estimated 

 (Elliott and Persson 1978) as 



r [S T - (S e-dT) ]rT 



u T = - — — - g food, 



-dT 



(4) 



where S T was the amount of food found in stomachs 

 at the cessation of feeding, and d = 0.106 (from Equa- 

 tion 3). No food was in the stomachs at the initiation 

 of feeding (S = 0). For 1 hour of feeding, C T equaled 

 1.054 St, and for 0.5 hour of feeding, C T equaled 

 1.027 S T . Thus, only a slight correction of mean stom- 

 ach content estimates was needed to calculate the 

 rations (Table 1). 



The water content of food (euphausiids) averaged 

 78.4% (N 9, SD 1.7%); therefore, dry mass averaged 

 21.6% of wet mass. The fat content of the food aver- 

 aged 21.8% of dry mass (N 3, SD 3.6). S. Kaupp 

 (NMFS Southwest Fish. Sci. Cent., P.O. Box 271, La 

 Jolla, CA 92037, pers. commun., March 1984) found 

 that the average protein content of euphausiids (species 

 not identified) was 43.5% of dry mass (N 25, SD 0.20). 

 The remaining dry mass (24.7%) was estimated to con- 

 sist of ash and chitin in roughly equal amounts, since 

 Lasker (1966) found that molts and ash each made up 

 about 10% of dry mass in Enphausia pacifica. Assum- 

 ing 9.2kcal/g for fat, 5.65kcal/g for protein, and 4.1 

 kcal/g for carbohydrate (Brett and Groves 1979), the 

 total caloric content of the food was 



21.8 „ „ kcal 

 92 



100 "' g dry 



43.5 kcal 



- 5.65 - 

 100 g dry 



12.4 

 100 



4.1 



kcal 

 gdry 



= 5.09 



kcal 



g dry food 



