PROBLEMS OF FISH AND FISHING 



306 



food; that is, if they were thriving and growing, they would 

 resist attacks of saprolegnia or other disease germs. A variety 

 of plants and animals is essential in a balanced pond if it is 

 to supply food continuously to all its inhabitants. As with 

 similar problems on land, the most necessary thing is an 

 abundance of plants, to supply food for snails, mussels, in- 

 sects, worms, Crustacea, and vegetable-feeding fishes; then 

 mussels should be present in sufficient numbers to strain out 

 any excess of floating 

 algse and fungi ; and, 

 finally, there must be 

 enough carnivorous 

 forms to prevent exces- 

 sive multiplication of 

 t he vegetarians. Of 

 course this natural bal- 

 ance of lakes and ponds 

 H a more complex mat- 

 ter than that of our 

 aquaria, since these are 

 never required to pro- 

 duce all the foods of 

 Ihe fishes. 



Fic " 143< Tray of wild - trout e s^ with mos- 

 quito net and moss in which they were packed 



United States Bureau of Fisheries 



Even good-sized lakes 

 may lose balance, and cer- 

 lain species may suffer. The white bass in Lake Mendota, Wisconsin, in 

 the summer of 1889, died in such numbers that windrows of them were 

 washed upon the shores, necessitating the removal of over 200 wagonloads 

 -rorn the mile or so of beach in Madison. They had become overcrowded 

 and weakened by starvation. Lake Louise, in Pennsylvania, was stocked 

 with black bass, and the rules of the fishing club that controlled it required 

 that all the fish caught be returned to the lake. In a few years the lake 

 :iad nothing but black bass in it, and these were so starved that the 

 lish were almost all heads and mouths, with shrunken bodies. The case 

 vas investigated by the United States Bureau of Fisheries, which 

 idvised fishing out the surplus black bass and transferring them to the 



