562 



Fishery Bulletin 89(4). 1991 



Figure 4 



Estimated rates of changes in fish energy content. Slopes were 

 converted into mass-specific rates of caloric growth at the 

 high-ration level for (A) slow-swimming and (B) fast-swimming 

 speeds and at the low-ration level for (C) slow-swimming and 

 (D) fast-swimming speeds. Negative slopes from the zero- 

 ration treatments were converted into mass-specific rates of 

 energy loss for (E) slow-swimming and (F) fast-swimming 

 speeds. 



feeding levels, caloric growth was greater in the slow- 

 speed than in the fast-speed treatments. In each treat- 

 ment, energy utilization (in cal • g _1 • day -1 ) not ac- 

 counted for by maintenance metabolism (Q M ) and 

 caloric growth (B + F) was a relatively constant frac- 

 tion of the energy consumed: 



About 35% of the food energy was lost through excre- 

 tion (X), digestive losses (I), and SDA, so the energy 

 budget Equation (5) may be simplified as 



R = (B + F + Q M ) / 0.65 cal • g" 1 • day 1 . (6) 



Observed gross conversion efficiency (K) was calcu- 

 lated by dividing caloric growth (B + F) by ration (R). 

 Gross conversion efficiency predicted by the energy 

 budget approximation (Equation 6) was 



K = - — (dimensionless). 



R 



(7) 



The model closely matched the observed gross conver- 

 sion efficiencies: 



Gross conversion 

 efficiency (%) 



High ration, slow speed: 

 High ration, fast speed: 

 Low ration, slow speed: 

 Low ration, fast speed: 



These results indicate that a simple energy budget 

 model, assuming a loss of 35% of the food energy due 

 to X, I, and SDA, explains increased growth with in- 

 creased ration and decreased growth with increased 

 activity. 



Discussion 



Gross conversion efficiencies 



The energy budget approximation (Equation 7) implies 

 that gross conversion efficiency is reduced by low ra- 

 tion and high activity. This was supported by the lower 



Ration - Growth - Maintenance = Excretion + Digestive losses + SDA 



(R) (B + F) (Q M ) 



High ration, slow speed: 55.7 - 21.5 - 0.9(17.6) = 



High ration, fast speed: 52.0 - 8.1 - 0.9(28.2) = 



Low ration, slow speed: 37.6 - 7.5 - 0.9(17.6) = 



Low ration, fast speed: 37.2 - 0.3 - 0.9(28.2) = 



(X) 



(I) 



