188 American Fisheries Society. 



it can readily be seen that the figures are not excessive. It will 

 also give an idea as to the immensity of the work. 



During the season of 1921, there were 178,100,161 miscel- 

 laneous fishes rescued and returned to the main river. Of these 

 506,394, or 29-100 of 1 per cent were shipped elsewhere to stock 

 lakes and streams. The average cost in all fields in 1921 was 17.3 

 cents per thousand. When the work was first undertaken a num- 

 ber of years ago the cost was $3.18 per thousand. 



Comparison of the cost of the rescue work with that at a 

 station is clearly in favor of the former. The average cost of pro- 

 duction of warm water fishes at a pond station is approximately 

 $5.50 per thousand, while rescue operations have handled the same 

 species at a cost of 13.5 cents per thousand, the cost varying witfi 

 the price of supplies and labor conditions. If the fish rescued 

 during the season of 1921 had been purchased from commercial 

 dealers or reared at pond stations, the cost to the Bureau would 

 have been approximately $979,550, while the actual cost, exclusive 

 of the salaries of the regular employees, was $30,811. The com- 

 parison is obvious. 



In connection with the rescue of stranded fishes, such species 

 as are suitable hosts for larval mussels are infected with the glo- 

 chidia and released ; thus a double service is accomplished with only 

 a slight increase in cost of the work as the same men perform 

 both services. 



The pearl button industry of this country is dependent on the 

 mussels of the Mississippi River and its tributaries for raw mate- 

 rial, hence keeping up the supply is of more than local importance. 

 There is probably not a man, woman or child in the United States 

 today on whose clothes there are not pearl buttons manufactured 

 from Mississippi River mussels. There is no other known mate- 

 rial as suitable for buttons of this type as the fresh water mussel. 



In nature the mother mussel liberates the baby mussel when 

 the gill pouches become filled with ripe mussels, and the little mus- 

 sels pass out into the water with no known destination. If the 

 proper fish, or host as it is known, happens to be swimming by, 

 all well and good; the little fellow is carried on the gills as the 

 fish breathes, and fastens there and stays until it has reached the 

 stage when it can begin life on its own initiative. The length of 

 time the larval mussel is carried on the gills of the fish is depend- 

 ent on the temperature of the water. If no fish happens by when 



