76 U. S. BUREAU OF FISHERIES 
quantities, produce definite toxic effects. The trout become dark 
colored and eventually die. 
Feeding and nutrition experiments conducted at the cooperative 
hatchery at Cortland, N. Y., are discussed in a separate section of 
this report. 
Selective breeding—Breeding experiments with brook trout were 
continued at the Pittsford (Vt.) Hatchery and have resulted in 
more than doubling the rate of growth and also the production of 
eges. Strains of fish also have been developed that are more resist- 
ant to hatchery diseases, especially furunculosis. 
Breeding experiments with rainbow trout are being carried on at 
the Leetown Station, but have not yet been continued long enough 
to produce significant results. 
WARM-WATER FISHES 
Studies on the black basses and other warm-water fishes are being 
conducted at the Leetown and Welaka (Fla.) stations. Hatchery 
and field investigations were carried on at both stations, but at Lee- 
town the smallmouth black bass received most attention, while at 
Welaka the largemouth black bass was the center of interest. 
Studies at Leetown.—The work on smallmouth bass streams in this 
region, under the direction of E. W. Surber, was confined to (Up 
the collection of 100 adult smallmouth black bass for food and par 
site studies from each of the following streams: Cacapon Hives 
South Branch of the Potomac River, and the Shenandoah River; 
and (2), the collection of temperature and turbidity records in the 
Shenandoah River. 
Previous studies on the spawning of smallmouth bass in these 
streams have shown that large numbers are hatched each year, but 
that the number of young bass decreases rapidly a short time after 
they leave the nest. The loss is probably greater than in hatchery 
ponds under ordinary conditions. A large part of this loss in 
streams is believed to be due to pr edacious fish, especially young 
smallmouth bass in their second and third year of life. Some of 
the loss appears to be caused by parasitization. 
Experimental work at Leetown has been limited, due to lack of 
suitable ponds. However, 28 new ponds, designed especially for 
experimental work, were completed during the “past year and will 
be available for use in 1940. Some experiments with forage fish, 
carried on during 1939, demonstrated that when ponds are stocked 
heavily with black-head minnows before smallmouth bass fry are 
added, large numbers of fry disappear, presumably because they 
are eaten by the minnows. Largemouth bass fry, however, have a 
better chance of survival. The results indicate that 1,000 to 3,000 
black-head minnows per acre can be used successfully 1f ponds are 
not stocked with minnows until the bass fry are too large to be 
eaten. 
Studies at Welaka—The work at this station is under the direction 
of O. Lioyd Meehean. During the season 1939 only 8 ponds were 
available for experiments, and were fertilized with cottonseed 
meal at weekly intervals. Four ponds were stocked with bream 
(bluegills) and golden shiners to serve as forage, and the remaining 
4 ponds were stocked with largemouth black bass only. The ponds 
