Staple Foods 



389 



The food relations of aquatic organisms are exceed- 

 ingly complex. They change with age and season and 

 situation. The eater and the thing eaten often 

 exchange roles. Yet there are some fairly constant 

 food dependencies between the major groups of 

 organisms. These have been set forth by that veteran 

 student of the forage problem, Prof. S. A. Forbes, in the 

 table copied herewith (fig. 233), and this table indi- 

 cates (what detailed food studies at large abundantly 

 confirm) that fishes eat almost every living thing that 

 the water offers. 



FIG. 232. The nymph of the dragonfly, Anax 

 junius, devouring a small sunfish. 



The young of all fishes eat plancton. This sounds 

 like one point of general agreement, until we reflect 

 on the variety of organisms of which plancton is com- 

 posed. Which of these are best for use in fish culture 

 we scarcely know at all. Fortunately, they are of 

 nearly universal distribution in shoal fresh waters, 

 where the young of fishes are found. 



Staple foods While a list of all foods, eaten by all 

 fishes would include practically every thing that is 

 found in the water, yet when careful food studies are 

 made there are a number of organisms so constantly 

 recurring that they stand out as of prime importance. 

 A few aquatic herbivores are found as commonly and 



