BIOLOGICAL STATION, FAIRPORT, IOWA. 11 



governed by distribution of air or waste gases in the water, and the 

 quantity of animal hfe in the pond is limited by the supply of dissolved 

 gases. 



Since the air supply of fish, without which they can not live, varies 

 both seasonably and irregularly, the investigators must study the 

 conditions of occurrence and distribution of gases in ponds and 

 streams that wo may learn what is favorable and what is unfavorable 

 to the best conditions of gas content and thus to productivity of 

 useful animals. 



Since the air and the chemicals of water and soil arc brought to 

 the fish through the intermediation of small plants, small floating 

 animals, creeping insects, and other things, these must all be carefully 

 considered in their relation to fish culture. The relations are com- 

 plex and the investigators must concentrate attention in difi"erent 

 studies upon particular animals or plants. Some of the investiga- 

 tions so far pursued at Fairport relate to the food of the fishes at 

 various stages of development, the kinds of plants that are most 

 suitable and necessary in fish ponds, the relations of certain insect 

 larvie as food or as enemies of fish, and the occurrence of parasites 

 that weaken the growing fishes and cause them to die or become an 

 easier prey to enemies. 



OTHER SERVICES TO FISHERIES. 



A good deal of valuable work which is not directly related to 

 mussels or to fish culture is done at and from the Fairport station. 

 A few typical forms of service may be cited. 



The construction of the dam across the Mississippi River, about 

 100 miles below Fairport, at Keokuk, Iowa, gave opportunity for a 

 comprehensive investigation of the efl^ects of water-power develop- 

 ments upon the fisheries of large rivers, and considerable information 

 has been gained as the result of observations continued over a period 

 of several years at Keokuk and at various points both above and 

 below. 



Chemical studies pursued in the laboratory have been directed 

 toward ascertaining the food qualities of some aquatic products and 

 possible methods of improving them. 



Studies of the diseases of fishes, the causes and remedies, have been 

 pursued. It has been learned that the slight injuries incidental to 

 the handling of fish in warm weather, particularly in rescuing fishes 

 from overflow waters, often lead to bacterial infections which cause 

 serious mortalities. Means of prophylaxis are being devised which 

 may be simple of application and effective in materially increasing 

 the effectiveness of rescue operations in warm weather. 



Somewhat apart from the ordinary lines of activity of the station, 

 but corresponding to an evident need existing along the Mississippi 

 River, there were conducted during a period of years some simple 

 but immediately practical experiments in smofeing the common 

 fishes of the Mississippi River which had no particular value in the 

 fresh state and which brought so little return to the fishermen that 

 they were often allowed to go to waste. Some of these were occa- 

 sionally smoked, but in many cases the smoking was so carelessly 

 or ignorantly done that the product was inferior in taste and in keeping 

 quality. Others were thrown away or sold for nearly nothing. The 



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