1918 Fasten; on Fish Lice 75 



flesh to swell and develop a large amount of scar tissue (Fig. 2), which 

 interferes considerably with respiration. Bacteria and other organisms 

 may make their way into the injured portions of the trout and cause 

 infections of a serious nature. Taking all these facts into consideration, 

 there is little wonder that fish succumb under the attacks of these para- 

 sites, particularly in hatchery ponds where conditions are just right for 

 parasitism. In one Wisconsin hatchery the author found that in a single 

 year about 12,000 adult trout out of 14,000 kept in outdoor ponds died 

 from the attacks of these copepods. 



Many states have had this trouble for years, with very serious losses. 

 The writer has devoted 'considerable attention to the control of these para- 

 sites, and has recommended the following remedies in the state of Wis- 

 consin. These may also be found of use in our own hatcheries. 



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. 



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

 the adult copepods during the early stages of attachment. At the same 

 time the salt makes the fish more resistant. 



3. Since the adult trout are the ones most heavily parasitized, it is 

 better to keep only the younger fish for spawning purposes. 



4. Since the free-swimming stages of the copepods 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 

 illuminated regions, the copepods can be gathered and removed. 



5. 'The introduction of certain types of minnows into the hatchery 

 ponds tends to keep the parasites down. These minnows feed on the free- 

 living larvae of the copepods and thereby destroy many of them before 

 they have the opportunit}' of coming in contact with the proper host. 



Although these remedies are not absolute, they may nevertheless tend 

 to reduce the loss from the parasitic organisms enormously. There is no 

 absolute cure known. A most desirable remedy would be one which would 

 destroy the adult copepods while they are attached to the fish, without in 

 any way harming the host ; but all attempts in this direction have thus 

 far been without success. Trout are so delicately constituted that they 

 can withstand only a very slight change in their environmental medium. 

 The adult copepods, on the other hand, can resist powerful chemical solu- 

 tions by virtue of their resistant body walls. One must catch the organisms 

 as they break out of the egg cases of the mother, and kill them before 



