No. 640] PARASITIC COPEPODS 



455 



attention to the control of these parasites, and has recom- 

 mended the following remedies in the state of Wisconsin. 

 These have also been found useful in other states where 

 the same type of parasitism has made its appearance. 



1. When the water supply is polluted, sand filters 

 should be installed at the mouth of the water stream as 

 it makes its way into the hatchery ponds. The sand 

 catches most of the free copepods before they enter the 

 hatchery, thereby preventing them from attacking the 

 fish. 



2. The young fry should be given salt baths quite often. 

 The salt solution kills the copepods, during the early 

 stages of attachment, ^t the same time this solution 

 makes the fish more resistant to the attacks of the 

 parasites. 



3. Since the adult fish are the ones most heavily para- 

 sitized, it is better to do away with these as soon as 

 possible and to keep only the younger fish for spawning 

 purposes. 



4. Inasmuch as the free-swimming stages of the cope- 

 pods are strongly attracted by intense light, powerful 

 arc lights should be erected at various points over the fish 

 ponds. By means of fine gauze bags towed over the illu- 

 minated regions, a large number of the copepods can be 

 gathered and removed. 



5. The introduction of certain types of minnows into 

 the hatchery ponds tends to keep the ]iarasitos down. 

 Tliese minnows feed on the free-living larv.-v of tlie cope- 



lio>t. " ' ' 



Anotli. r iiiran^ nf ovriv.milim' tl.i> sort of parasiti>m 

 \vlii<-li h;i. u\'\vu mi-uvM.mI itH^ir to tho wi-it.T is, thror-n 

 bree.lin-. to .l.'vclo]. a >train ainoii.o>t the ho>t^ which 

 would hr practically iiHinimo to the atta.'k^ of tlie jnira- 

 sites. Tills ajiru'ars to be possible wiicii one ronshh-rs the 

 fact that undov similar .'oii.lition^ the ho.f. >|,ou- varying 

 degrees of resistance to the parasitic organisms. Some 



