ELEVENTH ANNUAL REPORT. 101 
ROCK BASS. 
without fishes, until the use of a seine in one corner showed 
that the yellow perch fry introduced two years before had already 
attained good size. The presence of snags elsewhere in this lake 
prevented the use of the net. The management of this pond will 
always be difficult and unsatisfactory. 
A lake in the Zoological Park, stocked with yellow perch fry in 
1903, Was represented to be without fishes, until the use of a 
seine, sent from the Aquarium a year later, showed it to be well 
supplied. The full utilization of this lake is however impossible, 
since its bottom has many scattered rocks which prevent effective 
seining. If the rocks had been removed originally, a good sized 
seine would sweep it from end to end. 
Water Supply.—The water supply of the fish-pond is the most 
important thing to be considered. It must in fact be taken into 
consideration before the artificial pond is made. The flow of 
water should be abundant. About twice as much will usually be 
required as the beginner thinks is necessary. 
Ponds fed by strong springs are excellent and are not subject to 
the dangers to which stream-fed ponds are exposed. Their tem- 
perature is naturally more equable throughout the year and they 
are less liable to heavy freezing in winter. In warm weather 
and in the winter time, pond-fishes avoid extreme temperature by 
frequenting the vicinity of bottom springs. Spring-water, how- 
ever, contains less life available as fish food, and less air than 
