AGE AND GROWTH OF THE CISCO 
309 
“space-factor”, whereby crowding alone impedes growth independently of the abun- 
dance of food. 
24. Since, with the exception of a reversal of the positions of the closely similar 
Muskellunge Lake and Silver Lake populations, the four lakes arrange themselves in 
the same order with respect to the density of their cisco populations and with respect 
to the concentration of bound C0 2 in their waters, it was suggested that differences 
(traceable to the concentration of bound C0 2 ) in the kind and abundance of plankton 
available to newly hatched ciscoes may account for the observed differences in the 
densities of the four cisco populations. 
25. Although the relationship between parasite infestation and growth rate has 
not been thoroughly investigated in the cisco it is known that the Clear Lake cisco, 
which has by far the best growth of any of the four populations, is practically free 
of parasites (96 percent negative), while the slower-growing populations from Silver, 
Muskellunge, and Trout Lakes have a heavy infestation of intestinal parasites 
(80 percent, or more, positive). 
26. The best growth of the cisco occurs in Clear Lake with the smallest amount 
of organic matter in the surface plankton, but Muskellunge Lake, with the greatest 
amount of organic matter in the surface plankton does not have the slowest-growing 
cisco population. 
27. The order of the four lakes with respect to the value of the sex ratio (females 
per 100 males) is the reverse of their order with respect to the rate of growth (in weight). 
It was suggested that the same factors that determine the rates of growth may cause 
the differential mortality rate of the less viable males to be greater in the slower- 
growing populations. 
28. The Clear Lake cisco with the most rapid growth is in the best average con- 
dition (highest average value of K) and shows the most rapid improvement of con- 
dition with increase in length, but the Muskellunge Lake cisco with the poorest average 
condition and the most rapid loss of condition with increase in length is not the popula- 
tion with the slowest growth. 
29. The at least partial independence of the factors that determine growth rate 
and the factors that, determine condition may be construed as a strong argument for 
the operation of the “space-factor” in the determination of growth rate. 
30. The order of the four lakes with respect to the average condition of their 
cisco populations and the rate of change of condition with increase in length is the 
reverse of their order with respect to the abundance of organic matter in the surface 
plankton. Thus it appears that the poorest condition is found in the most eu trophic 
environment and the best condition in the most oligo trophic environment. 
31. Longevity and condition appear to be correlated. The average life span 
of the cisco is shortest in Muskellunge Lake where the average condition ( K ) is 
poorest and increase in length is accompanied by a rapid loss of condition, and the 
longest in Clear Lake where the average condition is best and condition improves as 
length increases. 
32. In a general review and summary of the growth relationships of the cisco, 
it was brought out that some of these relationships fail to conform to generally 
accepted theories. The need was mentioned for a broaderlknowledge of the biology 
of the cisco based on observations in a great diversity of habitats. Attention was 
called to the danger of premature generalizations concerning the growth relationships 
and the biology of this very plastic species. 
