96 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



Supplies of dead limbs from the linden tree are obtained from Massa- 

 cbnsetts avenue and also on B street, iSW., after heavy wStorms. Sub- 

 seqnent trials with sycamore boughs were rather encouraging-. The 

 newly acquired knowledge led to the adoption of air liberators in all of 

 the aquaria at Central Station, and formed tlie basis of the circulating 

 process adopted a few weeks later in the fourth special car added to the 

 distribution service. It also resulted in effecting the permanent intro- 

 duction of an air compressor, with small iron piping- as a conduit, in 

 Central Station. Prior to this the aquaria had been supplied with air 

 by a crude method, described on pages 2 and 3, United States Fish 

 Commission Bulletin, 1890. 



Fish Ponds, Washington, D. C. (Rudolph Hesskl, Superintendent). 



The product of this station consists of fingerling fish, there being 

 annually stored and reared in one or more of the ponds, additional to 

 the regular work, an average of 2,000,000 young shad, which are released 

 in the fall months when they have attained a length of 3 to 4 inches. 

 One of the difliculties met with here is in keeping down the growth of 

 vegetation in the ponds. Since the flood of May, 1889, its removal has 

 required the expenditure of a large amount of labor from May to Nov- 

 ember. Men go overboard with mowing- scythes and cut the plants 

 near the bottom, afterwards gathering with small boats and wooden 

 rakes for transfer to the shore. The great weight of this material makes 

 its removal laborious, even after placed on the banks; wheelbarrows 

 are employed in transferring it to portions of the grounds where it can 

 be put out of sight. In July probably 400 cart-loads were removed. 

 It is necessary each October to thoroughly remove the vegetation to 

 afford free passage of fish from all parts of the ponds to the receivers, 

 otherwise the fish will not collect at the points desired, but scatter over 

 the areas and be lost under the growth. 



The drawing- off of ponds commenced November 21, when the sorting 

 and counting of fish was begun and continued for a period. The pond 

 containing black bass was drawn December 1, and the sorting and 

 counting occupied almost a week. Almost as quickly as ponds were 

 freed from the year's production, it became necessary to take up their 

 cleaning and preparation for another year's work, banks having been 

 injured and the trenches in the bottoms leading to the collectors being 

 filled with mud. 



Carp. — The now x)ond, 5 acres area, being partitioned off, leather carp 

 ■were produced on one side and scale carp on the other. Two small 

 l)onds, 40 by GO feet each, were devoted to the blue-leather and blue- 

 scale varieties. 



Spotted catjifih. — No definite observations could be made concerning 

 the spawning habits of this fish, as it was in hiding during the spawn- 

 ing- season. There were 8 spawning fish in the ponds, producing 1,300 

 young. 



