8 REPORT OF THE COMMISSIONER OF FISHERIES. 
mals of the land can be made responsive to the application of scien- 
tific principles and experimentation, so the culture of the products 
of the ponds, lakes, and rivers may be increased by discovering 
the favorable and the limiting factors of production. The necessary 
investigative work involves careful studies of conditions character- 
istic of rich and poor waters, observations of the relations existing 
between fish and the other animals and plants with which they are 
associated, and experimental work to test the effect of particular 
factors upon the growth and multiplication of fish. 
While scant special provision has been made for strictly fish-cul- 
tural experiment work, the Bureau endeavors to take advantage of 
such opportunities as are offered for work of this character, and these 
are found principally at the fisheries biological station at Fairport, 
Towa. Experiments are conducted at that station to appraise the ca- 
pacity of small ponds to support fish life, to determine the best plans 
of pond management, to discover what species of aquatic plants or 
animals should be introduced or fostered in fish ponds, and to make 
fish-cultural methods applicable to species of fish not hitherto propa- 
gated by artificial methods. Some experiments have also been con- 
ducted in connection with fish-cultural stations to discover means 
of reducing losses of eggs, fry, and brood stock, and of preventing 
deterioration of fertility of brood stock. If adequate and perma- 
nent provision could be made for the facilities and personnel of 
experimental work of this nature, the interests of economy would be 
served in the long run by increasing efficiency in all fish-cultural 
operations affected. One of the results incidentally obtained at the 
Fairport station—the devising of a new form of pond outlet which 
has stood the test of several years’ trial—has shown the possibility of 
effecting substantial economies in the construction and maintenance 
of ponds at all stations where earth ponds are used. 
Another means of effecting permanent economies in fish-cultural 
operations can be found in the reduction of disease or other causes 
of mortality in hatcheries. To serve this purpose, the primary neces- 
sity is a competent and permanent employee for the study of fish 
diseases. The need was recognized by Congress when in 1915 it 
established the position of fish pathologist as a part of the regular 
scientific personnel of the Bureau. During the six years which have 
elapsed since the position was created it has been vacant for one-third 
of the time and during the remainder has been held by three incum- 
bents, none remaining in the service long enough to make more than 
an encouraging beginning. The difficulty has been that the salary 
was inflexible and fixed at too low a rate to attract and hold the 
proper man. The remedy is easily found in a readjustment of salary 
conditions such as has been referred to in a preceding paragraph. 
The position of fish pathologist was occupied during half of the past 
fiscal year, and investigations were directed at the ovarian diseases 
of fishes and the high mortality rate prevalent in all pike-perch — 
hatcheries. Utilizing the services of temporary investigators, the 
Bureau has also made investigations of the losses of fish rescued in 
warm weather, finding a practicable remedy, and studies of in- 
jurious parasites of fishes. 
