i^200 



2 4 6 8 10 12 14 16 18 20 22 24 26 28 



WEEK NUMBER 



Figure 2.— Inituil growth of populations. Dat;t are means for the three popidations at each diet level. 



were in ratios 1.00:1.79:2.52 as eoinparcd with 



iho 1 :2::; i-atius n( ilie diet lexels. 



Axeracre luiinhers „f fish fell even fartlier iVoin 



tlie ratios of the diet levels than did the avera.i-e 

 weights. For weeks 21 to 28 they were 110, 145, 

 and 149 in ratios 1.00:1..32 :1.35. Comparison of 

 lliese ratios with those for average weights indi- 

 cated that the individual fish averaged larger at 

 file higher diet levels. Weights of indivi.lual fish 

 averaged 0.1.32, 0.179. and 0.246 g., respe.-livelv. 

 Ml populations at diet levels 0.5, 1.0, and 1.5. 



These results indicate that the greater biomass 

 at the higher diet levels than at the lowest level 

 was caused by both better survival and more 

 rapid growth of individuals. Growth was the more 

 "n|<-rtant factor. The results indicate also some- 



430 



what less efficient food use at the higher diet 

 levels than at the lowest, in the sense of the 

 amoimt of biomass supported by a given atnouiu 

 of food. Thus, the 2.,S5 g. of food consumed i)er 

 week (totals for Daphnia and dry food from table 

 1, plus 6 times 'A of 0.000125 g. for Art^mia), at 

 the 0.5 diet level supjjorted a biomass of 14.5 g., 

 or 5.1 g. per gram of weekly consumption, whereas 

 at the 1.5 diet level the comparable figures are 

 8.55 g., 36.6 g., and 4.3 g. This loss of efficiency 

 may have been the result of crowding the larger 

 biomass at the higher diet levels into the same 

 amount of space as occupied by the biomass at 

 the lowest diet level. Altermilivcly, it is po.ssible 

 that such efficiency may simply be a deelining 

 fimction of .size in stabilized j)opulations. 



U.S. FISH .\ND WILDLIFE SERVICE 



