96 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
Supplies of dead limbs from the linden tree are obtained from Massa-— 
chusetts avenue and also on B street, SW., after heavy storms. Sub- 
sequent 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 the 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 HESSEL, 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 5 to 4 inches. 
One of the difficulties 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 new pond, 5 acres area, being partitioned off, leather carp 
were produced on one side and scale carp on the other. Two small 
ponds, 40 by 60 feet each, were devoted to the blue-leather and blue- 
scale varieties. 
Spotted catfish.—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. 
