REPORT OF THE COMMISSIONER OF FISHERIES. 17 



the Mississippi Valley, but particularly for the cultivation of the 

 mussels employed as raw material in the pearl-button industry, a 

 manufacturing interest giving employment to a large number of 

 persons. 



Progress has also been made in the construction of the substation 

 at Homer, Minn., which recent investigations show can be employed 

 for various economic purposes connected with the fisheries, in addi- 

 tion to mussel culture. 



EXPERIMENTS IN SPONGE CULTURE. 



Although the experiments in growing sponges from artificial cut- 

 tings have already developed what the Bureau regards as a prac- 

 tical system of sponge culture, work is still being carried on with 

 the purpose of improving the methods and testing the effects of 

 different environments on the rate and character of sponge growth. 



The sponges grown in Cape Florida Channel, which, as reported 

 last year, attained an average weight of 1.25 ounces each at the end 

 of twenty-nine months, were found to average 2 ounces ten months 

 later, some of the largest specimens weighing from 3 to C> ounces 

 each when thoroughly cleaned and dry. The same disparity in the 

 rate of growth of different specimens observed in other localities 

 was found to occur in this place, while at Soldier Key, about 7 miles 

 distant, where the conditions appear to be equally favorable, growth 

 was very slow. 



STUDY OF FISH DISEASES. 



During the fiscal 3 r ear the Bureau has continued cooperation with 

 the New York State Cancer Laboratory in the investigation of thy- 

 roid tumor or cancer in domesticated fishes. An aquarium w T ith 

 two independent systems of closed- water circulation, with proper 

 means of refrigeration, has been established for the observation of 

 salmon and trout and experiments in inoculation and treatment. 

 Investigation at various stations of the Bureau and at other hatch- 

 eries have shown that the disease is even more widespread and gen- 

 eral than was suspected. Considerable difficult}^ has been encoun- 

 tered in obtaining for purposes of experiment a sufficient number 

 of fish above suspicion of infection, and it has been necessary in this 

 effort to secure a quantity of wild trout from remote streams. Owing 

 to the technical difficulties attending this work, which arc equal 

 to those -retarding the advance of knowledge relating to the cause 

 and nature of cancer in human beings, progress is made only by 

 slow and painstaking steps and by the use of the most approved 

 appliances and methods. For this reason it is highly important 

 that the Bureau should be provided with a well-equipped laboratory 



