FOOD AND PARASITES OF SOME FRESH- WATER FISHES. 



521 



The 39 perch in which insect larvae were found contained, as far as 

 we could determine, phryganid larvjB in but 1 and dragon-fly larvie in 

 9 fish. Thirt^^-six of the entire number contained but a single kind of 

 food, 15 had 2 kinds, 2 had 3 kinds, and 3 were found with •! kinds of 

 food. In nearly every perch in which more than one kind of food was 

 present, insect larva? were found. Forbes {]>) gives the food of the 

 perch he examined and we note a great similarity to what we recorded. 

 He found that a number of fish were eaten by the perch he examined 

 from Lake Michigan, due, no doubt, to the smaller amount of insects, 

 Crustacea, and moll asks present in the large lake. 



The following table will show the kinds of parasites found and the 

 abundance and distribution of each kind in their hosts: 



Trematodes 



Cestodes 



Nematodes 



Acantliocephala 



Stomach, 



Ccecal 

 tubes. 



Intestine. 



Gall 

 blad- 

 der. 



Clinudoiiium fitJerostoinum <m gill?, S; copepod [Ergasihis) on gills, 9; eestode and nematode liver 

 cysts, 39; cysts in mesentery, 6; cysts in wall of stomach, 2. 



The trematodes were nearly all Dhtomuni nodnlosiim^ which was by 

 far the most prevalent parasite. The number of times trematodes 

 were found in the gall-bladder was far greater than given in the table, 

 many fish having been examined without being recorded. In late 

 July and early August perch were found with a small immature 

 fluke present in considerable nund^ers in the gall-bladder, more than 

 half the specimens examined being so infected. It occurred to us that 

 this might be the young form of D. nodulosiim^ which is probable, 

 although, the specimens in the gall bladder being immature, it was 

 impossible to make a direct comparison. In more than half of the 

 perch examined the liver contained cysts; many of these we opened 

 and found that the}" inclosed either a j^oung eestode or a 3'oung nema- 

 tode. The nematode C3'sts were generally smaller and firmer than 

 those containing the cestodes, but it Avas impossible, unless every one 

 was opened, to be sure of the contents. There was undoubtedly Init 

 a single species each of eestode and nematode forming the cy^sts. 



The 16 perch caught during February through the ice were taken 

 much farther from shore than any of the others we examined. Four- 

 teen of these had fed exclusivel}' upon plankton. They contained as 

 large a proportion of encysted parasites as any of the other perch, 



