PROGRESS IN BIOLOGICAL INQUIRIES, 1922. 11 



42; carp, 40; buffalofish (Ictiohus cyprinella), 36; log perch, 35; 

 blunt-nosed minnow, 32; top minnow, 32; yellow perch, 31; shiner 

 (Notropis heterodon) ^ 30; Johnny darter, 30; black crappie, 27; 

 shiner (A^. atherinoides) ^ 14; bream, 11; shiner {N. hudsonius), 11. 

 In general, the fishes that frequent vegetation show the highest in- 

 fection with parasites; those that frequent the bottom and open 

 water are intermediate; and the small fishes that live in shallow 

 water have fewest parasites. 



The susceptibility of the host is an important factor in determin- 

 ing the degree and frequency of parasitic infection. Fish parasites 

 may show considerable specificity for certain hosts, and hosts may 

 possess a varying degree of immunity. The black bass, for example, 

 appears to be susceptible to many parasites that do not often attack 

 other Centrarchidae. Although the large-mouth and small-mouth 

 black bass are closely related, the latter always carried more para- 

 sites. Pumpkinseed were always more heavily infected than blue- 

 gill. Some of these differences may be due to differences in habitat ; 

 some are undoubtedly due to susceptibility. A general similarity be- 

 tween parasites of the Silurida? and certain of the Percidse is noted. 



Seasonal changes doubtless have a marked effect on certain para- 

 sites, but the observations are not conclusive. A previous investi- 

 gator has suggested that perch had few parasites when little food 

 was eaten on account of low temperature. In this investigation 

 perch were found to have more parasites in winter than in autumn 

 or summer, but it was the investigator's experience that perch did 

 not refrain from eating during winter. 



The size of the lake did not appear to be correlated with the degree 

 of parasitic infection of its fishes. The density of the population 

 may sometimes be of importance, but in general no direct relation 

 was observed between number of fishes and number of parasites. 

 On the whole, infection was found to be greater in shallow water, 

 probably because there is there a greater variety of habitats and of 

 secondary hosts. 



The conclusions from this investigation are not stated as definitive 

 or universal of application, but the results point to the need of more 

 studies of the ecology of fish parasitism.* 



During the last 8 or 10 years there has been noticed among winter- 

 fed yearling terrapins at Beaufort, N. C, two pathological condi- 

 tions, both of which lead to the death of the nonhibernating animals. 

 It has been observed also that among those yearling terrapins that 

 have been allowed to hibernate normally there was rarely found 

 any symptom of disease; the only exception would be an occasional 

 case of " soft shell." This condition, relatively common among dis- 

 eased winter-fed yearling??, is due apparently to faulty absorption 

 of the yolk sac after birth. The other death-producing condition is 

 a disease that generally attacks the tail at its veiy tip and causes its 

 rotting back to the body proper, where the disease destroys the 

 rectum and seriously affects the spinal cord, paralysis of the hind 

 limbs occurring and death following shortly. Often the flippers, 

 neck, and eyes of the terrapins become affected, and this condition 

 may result in preventing the terrapin from feeding. 



*The results will be published in the next volume (21) of the Transactions of the 

 Wisconsin Academy of Sciences, Arts, and Letters. 



