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, 

 Iowa. 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. Sortie 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 

 sen-ed 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-culturai 

 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 difiiculty 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. 



