The Way of Economic Progress 399 



vorous fishes, non-competitors for food, may therefore 

 be used to furnish a principal crop of animal forage. 

 For this use carp are objectionable because they grow 

 too fast and soon become too large to be swallowed by 

 the other fishes. They eat the eggs of bass, and root 

 up the bottom and tend to exterminate their own 

 vegetable forage. Minnows are also objectionable 

 because they eat the eggs of other fishes. But very 

 valuable for such use are the golden shiner (fig. 238), 

 and the gizzard shad, (Dorosoma cepedianum), of our 

 great rivers. Even the goldfish is an excellent agent 

 for turning masses of blanket algae and other soft fresh 

 vegetable foods into excellent forage for larger fishes. 



The way of economic progress The future of fish 

 culture lies in further scientific studies to be made 

 along the lines that have proven of value in the 

 raising of land animals. More knowledge is what is 

 needed : 



1. Intimate detailed knowledge of the fishes them- 

 selves is needed; knowledge of their natural history, 

 their requirements of food and of protection for 

 their young; their enemies, internal and external; 

 their natural races and possibilities of improvement by 

 breeding. Only such knowledge can fernish a 

 basis for developing methods of control. 



2. Equally detailed knowledge is needed of the 

 economic species that furnish forage or that menace 

 the welfare of the cultivated species; knowledge of all 

 the more important ones, from the forage fishes, crusta- 

 ceans, insects, snails, etc., even down to the diatoms. 

 The product must be followed to its principal sources 

 and the cultural relations that all these organisms bear 

 to each other must be better understood. The enemies 

 of every stage of fish life must be studied (fig. 239). 



