BULLETIN OF THE UNITED STATES FISH COMMISSION. 441 



Perch are about the ouly fish that are dying; at least 95 per cent, of 

 tbem are perch. There are a few white bass, still fewer sackers, and 

 an occasional pike and sunfish. (E. A. Brigs, Professor of Zoology, 

 University of Wisconsin, Madison, Wis., July 28, 1884.) 



Mr. Dunn's Theory. — Elaving for years past followed the business 

 of a fisherman for a livlihood, I am frequently asked, What kills the 

 perch in Fourth Lake? My suspicion was not aroused to a great ex- 

 tent until 1 saw, day by day, an unaccountable increase in the death- 

 rate. A living parasite or worm exists in the lake that causes the 

 trouble. The color of this parasite on first being taken out of the water 

 is of a light gray, with *,reen stripes crosswise of the body, about one- 

 half au inch in length. It is generally found where the weeds and grass 

 are the thickest, adhering to the stems of the grass and weeds where it 

 is easily seen by the perch who frequent these places iu quest of food. 

 The perch immediately detach the parasites from their hold, and they 

 are at once forced towards the stomach for digestion, but on reaching 

 the walls of the throat they fasten themselves as they do to the grass 

 in the lake. All eflbrts on the part of the fish to remove them are use- 

 less, as their adhering powers aie similar to those of a blood sucker. 

 The parties hejctofore examining the fish have nut beeu able to detect 

 this parasite, consequently their verdict was that nothing could be found 

 as to the cause of the deaths. The fish on coming to the surface are 

 almost dead, with hardly life enough left to move about. On examining 

 these you will almost in every case find nothing. Now and then you 

 will find some specimens containing this i)arasite fastened to the wall 

 of the throat iu the region of the gills. Then we must look there for 

 the cause of trouble. The parasite attacks the throat and causes intlam- 

 mation by irritating that part of the body. The fish is finally overcome 

 and strangulation takes place. In order to test what I say, catch some 

 perch in the neighborhood where there seems to be the most in a dying 

 condition. Let your line down to the bottom and you will have no 

 trouble in catching the fish. You will, in every case, find three to ten 

 of these parasites working in the throat of each fish. While the fit>h 

 are dying they release themselves and return to tlieir natural abiding- 

 place on the grass and weeds. The writer verily believes that no other 

 fish existing in the lake will feed upon these parasites except the perch. 

 If any other did partake of them, the same result would follow. 



In regard to the whitetish dying: It is nothing unusual, as more or less 

 die, according to the temperature of the water, every year. The hotter 

 the summer season, tbe more dead whitetish will be seen floating on the 

 surface. They live iu the coolest water in the lake, which is the deepest. 

 The presence of any large fish drives them out of their favorite place, 

 and being naturally very tender, when they pass into water of a great 

 deal higher temperature, death ensues. Try this experiment: Take 

 minnows out of the lake in the summer season and place them in well- 

 water; death follows. Now, take minnows iu winter-time out of the lake 



