FISHERY BULLETIN: VOL. 75, NO. 3 



carbohydrates, and proteins (Swift and French 

 1954). Active metabolism (Q) was derived by 

 multiplying standard metabolism (Q s ) measured 

 in the oxygen consumption experiments by 2.5. 

 Fry (1947) showed that the active metabolism in 

 small fishes was about twice the standard rate. 

 More recently, however, Ware (1975) demon- 

 strated in a re-analysis of Ivlev's (1961b) data 

 that active metabolism calculated for a variety of 

 growth rates and feeding densities could vary 

 between 2 and 3 times the standard rate. Recog- 

 nizing that active metabolism is a dynamic factor, 

 it is not unrealistic to assume a multiplier of 2.5 

 times standard metabolism for an estimate of 

 active metabolism. 



7. The number of hours (a) a larva of given 

 weight needed to feed to attain a given growth 

 rate at a given temperature and plankton concen- 

 tration was computed from Equation (9). 



8. Since winter flounder larvae were observed 

 in experiments to be visual feeders, the plankton 

 densities for each weight which predicted 12.0 h 

 feeding time (a) were identified. These were con- 

 sidered critical densities because feeding times 

 longer than this were ecologically impossible due 

 to unsuitable photoperiod. 



9. Food intake in calories was computed from 

 Equation (7). 



10. Metabolism or energy expenditure was com- 

 puted from Equation (5). 



11. Nonassimilated energy was computed by 



f 19. D- 



o.o too.o too. o loo.o too.o soo.o (oo.o roo.o 100.0 900. 1000. uoo.o 



OH* WIGHT (UG) 



FIGURE 6. — Number of daily feeding hours required by winter 

 flounder larvae to obtain energy for calculated growth and 

 metabolism as influenced by larval dry weight and planktonic 

 prey concentration at 8°C. Numbers for each simulated line 

 indicate prey concentration in calories per liter. 



536 



subtracting the energies of growth (Q') and me- 

 tabolism {Q (from the energy of food intake (Q + ). 

 12. Gross growth efficiency was calculated from 

 the formula: 



K, 



01 



where K 1 = gross growth efficiency and Q ' and Q + 

 are as previously defined. 



13. The percent body weight eaten per day was 

 calculated by dividing the caloric value of food 

 intake (Q + ) by the caloric value of the given body 

 weight. 



14. The number of naupliar or adult copepods 

 consumed per day at the given parameters was 

 calculated by dividing the caloric value of the 

 food intake (Q + ) by the previously defined aver- 

 age caloric value for nauplii or adults. 



MODEL SIMULATION RESULTS 



Daily Feeding Time and 

 Critical Prey Densities 



The number of daily feeding hours required to 

 meet growth and metabolism (a, Equation (9)) in 

 relation to larval dry weight and at plankton den- 

 sities which allowed feeding at some time within 

 the limits of the 12-h day length simulated by the 

 model is plotted in Figure 6. Feeding time at all 

 plankton densities was initially high for the 

 younger, smaller fish which later decreased before 

 increasing again to a peak around 500 /xg dry 

 weight, or when metamorphosis starts to take 

 place. A gradual decrease occurred during the 

 metamorphosis period (500-1,000 /xg larval dry 

 weight). As was expected, required daily feeding 

 times decreased with increasing prey density. 



The critical, minimal prey densities below 

 which longer than 12 h would have been required 

 to obtain energy to meet growth and metabolism 

 over the range of weights showed the highest 

 critical densities during the period corresponding 

 to first feeding with a decrease to a minimum 

 shortly after (10-75 fxg larval dry weight, Figure 

 7). An increase was then noted until the beginning 

 of metamorphosis (500 /xg) after which the critical 

 prey density gradually decreased to complete 

 metamorphosis (1,000 /xg). The range of critical, 

 minimum densities for the whole period was from 

 2.1 to 5.7 cal/liter, or approximately 0.3 to 0.8 

 nauplius/ml. 



