ARTIFICIAL. PEOPAGATIOlSr OF TEOUT. 59 



observations In connection with the Yellowstone Park operations we believe that 

 the following figures are approximately correct : 



^w-t,... Egg produc- 

 -'^se. (inches). tion. 



Yearlings 



Two-year-old „„ „„„ 



Three-year-old 8-12 500-800 



Four-year-old 11-15 800-1,200 



Thereafter 13-18 1,000-1,600 



On several occasions when we kept count of the fish spawned the average 

 production was found to run from 900 to 1,000 eggs per spawned fish. There 

 are very few undersized spawning fish as compared with brook trout, where 

 we find them producing spawn at 7 and 8 inches, and occasionally when even 

 smaller. It is believed that very few females spawn under 3 years of age in 

 the Yellowstone watershed. The season is short, due to both latitude and 

 high altitude, hence the rate of growth is somewhat slower than in many sec- 

 tions more favored climatically. 



PARASITES. 



This is an excellent food fish when fresh from cool waters, but the 

 trout from some parts of the Yellowstone Lake, Upper Yellow- 

 stone Kiver, and Heart Lake are generally reputed to be infested with 

 a parasitic worm. In his book pertaining to the fish of the park, 

 General Chittenden says : 



The trout of Yellowstone Lake are to a slight degree infected with a para- 

 sitic disease that renders them unfit for eating. Many efforts have been made 

 to discover the cause of this condition and a suitable remedy for it, but so 

 far without success. An explanation sometimes advanced is that the exces- 

 sive number of these fish and the absence of sufficient food reduce the vitality 

 and they become easy prey to parasites which a more vigorous constitu- 

 tion would throw off. Later investigations have shown that reports of the 

 prevalence of this condition were much exaggerated. 



The parasite referred to is a tapeworm, of which only the larval 

 or intermediate form occurs in the trout, the host of the adult being 

 an entirely different animal, as is the case with all tapeworms of this 

 kind. Briefly, its life cycle has been found to be as follows : Start- 

 ing with the egg in the water it develops into a ciliated embryo. 

 This passes into the fish, probably by way of the mouth, and becomes 

 established and assumes the form usually observed. The fish is eaten 

 by the pelican, and in the intestinal tract of that bird the parasite 

 attains its adult and reproductive stage and its round of life is 

 there completed. The eggs pass into the water and a new genera- 

 tion is begun. 



General Chittenden's statement that the parasite renders the fish 

 unfit for food involves a matter of prejudice rather than actual unfit- 

 ness for food or danger to the consumer. Cooking destroys the vital- 

 ity of the worm, and it may be said that this particular worm is not 

 harmful to man. Probably no one would knowingly eat an infected 

 fish, but if he should there would be absolutely no danger in doing so. 

 Beyond doubt the presence of this parasite is greatly exaggerated, as 

 General Crittenden says, and lean, cadaverous, unsightly trout, the 

 condition of which is commonly attributed to parasitism, are often 

 fish which are run down from breedii^ig, although they may carry 



