26 



U. S. BUREAU OF FISHERIES. 



place through invading cells, but is not always successfully accom- 

 plished; it apparently makes a demand upon the body of the fish, 

 which, if excessive, may lead to death. 



DISEASE OF RESCUED FISH. 



Dr. H. S. Davis, temporary investigator at the Fairport biological 

 station, has found that a high mortality may occur among rescued 

 fishes immediately after the handling incident to rescue operations. 

 This heavy death, rate is especially characteristic of the crappies, 

 buffalofish, and bluegills, when taken in warm weather, the first- 

 named species being the weakest. While the mortality may be 

 founded in part upon " shock " sustained during the seining and 

 handling operations, it is due more directly to bacterial infection 

 following slight injuries and gaining headway from the weakened 

 condition of the fish. Immersion for one minute in a solution of 

 copper sulphate in 1 to 1,000 dilution reduces the loss among rescued 

 fishes to a minimum. 



In certain experiments 75 to 100 per cent of the crappies rescued 

 from inland sloughs and untreated were lost through death. Under 

 similar conditions, except for a one-minute treatment with 1/1,000 

 copper-sulphate solution after the fish were allowed to remain a 

 short time in fresh clean water, this experimental loss w^as reduced 

 to 30 or 40 per cent. The necessity and practicability of the treat- 

 ment depend upon the conditions attending work in particular fields 

 and at particular times. It is believed that frequent tests should be 

 made in connection with rescue operations and the prophylactic 

 measures taken wherever a substantial mortality rate is to be ex- 

 pected. Dipping in a simple disinfectant can not be very expensive 

 and will be worth while if it will increase appreciably the percent- 

 age of survivors. 



Dr. Davis's experiments not only point out the possibilities of loss 

 and the means of prevention, but they also emphasize the necessity 

 for great care in handling rescued fish. Rough methods, including 

 the throwing of fishes into receptacles and the abrasion of the fishes' 

 bodies by seines, hands, or debris are the main causes of a high 

 death rate. 



PARASITIC FLATWORMS OF FRESH-WATER FISHES. 



The parasitic flatworms which infest the body surface and gills of 

 fishes (ectoparasites) may be more of a nuisance to fish culture in 

 ponds, tanks, or aquaria than those which live within the body of the 

 fish. The endoparasites generally can not complete the life cycle 

 without passing different stages in two or more hosts, which are 

 likely to be animals of widely different groups. Therefore, as re- 

 gards these parasites, fish can not directly infect fish. With external 

 parasites it is otherwise; there being no alternation of hosts, infec- 

 tion may proceed from fish to fish and thus multiply in such abun- 

 dance as to cause extreme weakness or death of the fish. Such a 

 parasite is Gyrodactylus fairy orti^ a new species described by Dr. 

 H. J. Van Cleave from bullhead and carp of certain ponds at the 

 Fairport (Iowa) station. These flatworms are very small, usually 



