104 U. S. BUREAU OF FISHERIES. 



Water penny (Psep?ienus lecontii, Lee.) Larva of a beetle. Common in swift 



water, clinging closely to underside of stones, occasionally at top or sides. 

 Fresh-water slirimp or " scud " ( Hyalella sp. ) Weedy portions of the stream ; 



rapid swimmers ; tail foremost. 

 Water net (Hydrodictyon reticulatum (L) Lagerh). A green alga of the 



pond areas of streams. When spread, it resembles a fine meshed veil ; a 



remarkable oxygenator. 

 Water moss {Hypnum riparium). Attached to stones or gravel in swift 



streams. 



Some species of plants and animals are of little value as indicators 

 of pollution, because they are found in both clean and polluted 

 waters. Snails, black-fly larvae, water boatmen, and similar forms 

 have a wide range and therefore are not good guides to water con- 

 dition, except to the scientist who can distinguish the different 

 species. 



Indicators of pollution may be summed up thus : 



Water molds and scums, particularly if of colors other than 

 green, indicate decreasing oxygen — conditions are not favorable and 

 may be worse downstream. 



Tubifex (a small, slender, red earthworm) marks approximately 

 the limit of fish life. 



Rat-tail maggots, if abundant over the whole bed of the stream, 

 are an almost certain indication of prohibited pollution. 



Bloodworms indicate recovery and conversion of wastes into fish 

 food. 



Green plants, mosses, silks, and nets usually indicate good and 

 improving conditions. 



METHOD OF DISTRIBUTION. 



In making distribution of fish consideration is first given to the 

 waters from which the fish or fish eggs were collected, after which 

 shipments are then made to suitable public or private waters upon 

 applications previously submitted. Blanks on which formal re- 

 quests for fish may be made are furnished by the bureau. These 

 blanks call for a complete description of the waters to be stocked, 

 and from this information are determined the species of fish that is 

 suitable and the number that can be apportioned to the water area 

 in question. 



The bureau finds it impracticable to investigate the condition of 

 all streams to determine their suitability for particular species of 

 fish, although such a study would be highly desirable, as it would 

 afford a basis for intelligent assignments. Since this is not prac- 

 ticable at present and the bureau is required to rely on information 

 furnished by applicants, it is decidedly important that such in- 

 formation be as accurate and complete as possible. 



Applicants are notified immediately upon receipt of their reqitests 

 concerning the species assigned and the approximate date of deliv- 

 ery and are given full directions for receiving and caring for the 

 fish. Before shipment is made a second notice is given, usually by 

 telegram, stating the exact time of arrival of the fish at the railroad 

 station. The fish are delivered at the station without expense to 

 the applicants. In the event that it becomes necessary to delay 

 shipment the applicant is notified accordingly. 



