AGE AND GROWTH OF THE CISCO 
289 
It is possible that an explanation of the differences in the lengths of the growing 
season may be found in the study of the plankton cycles in the four lakes. Particular 
attention should be given to the abundance at all times of the season, and in the strata 
actually inhabited by the cisco, of the plankton forms most commonly taken by that 
species. 
A second possible explanation of the differences in the length of the cisco’s growing 
season in the various lakes is suggested by the fact that in fishes in general the termi- 
nation of the season’s growth in adult fish is coincident with the onset of the develop- 
ment of the gonads preliminary to spawning. (The determination of the length of the 
growing season in the four cisco populations was based almost entirely on mature and 
maturing individuals.) Since the average size (weight) of the spawning individuals 
of the four populations follows the same order as their growth rates and the lengths of 
their growing season, it is suggested that the development of the gonads in small 
spawners may begin earlier in the season than in large spawners, and that the slowness 
of growth of a slow-growing population may be thereby accentuated. 
PARASITIZATION 
The only published data on the incidence and severity of parasitization in the 
cisco populations of Trout, Muskellunge, Silver, and Clear Lakes are those presented 
by Dr. Chancey Juday in the Bureau of Fisheries’ report on Progress in Biological 
Inquiries 1931 (Higgins, 1932). Juday summarized the data then available as 
follows: 
Thirty ciscoes from Silver Lake were examined for parasites, and cestodes were found in the 
intestines of all of them; 80 percent of them also had Acanthocephala. In Muskellunge Lake 80 
percent of the ciscoes contained cestodes and 20 percent were free of visceral parasites. In Trout 
Lake 16 percent were negative, 82 percent had cestodes in their intestines, and 10 percent also had 
Acanthocephala. The ciscoes from Clear Lake, on the other hand, were 96 percent negative; only 
2 specimens out of 60 examined yielded any parasites. These fish were found to be feeding almost 
exclusively on Daphnia, and this may be partly responsible for the very small parasite infestation. 
Clear Lake also has very soft water, and the snail population, as a result, is relatively small, so that 
the danger of parasite infestation from this source is correspondingly small. 
Although the above data show that the Clear Lake cisco with the fastest growth 
rate has the lightest parasite infestation, the relationship between parasite infestation 
and growth rate in the remaining three populations is not clear. The solution of the 
problem concerning the relationship between growth rate and parasite infestation in 
the cisco awaits the examination, within each population, of the effect of individual 
parasitization on individual growth rate. 
CONDITION 
In the section that dealt with condition and the relationship between length and 
weight it was pointed out that the order of the four lakes with respect to the average 
condition of their cisco populations, from poorest to best, is: Muskellunge, Trout, 
Silver, Clear. While this arrangement does describe the order of the lakes with 
respect to condition as based on the samples taken, it is open to the criticism that 
because of the variation of K with length, additional samples taken in yet other years 
and showing different length distributions of the fish might possibly bring about a 
change in the arrangement. The determination of an average value of K within a 
population depends, first, on the manner of change of K with length and, second, on 
the length distribution of the fish used . 
