2o6 College of Forestry 



The bottom animals may also be divided into producers, 

 those that live on detritus and plants, and the consumers or 

 those that are carnivorous and feed upon the producers. Some 

 of the latter may be both producers and consumers if they 

 vary their carnivorous diet with detritus or plants, as does the 

 pond snail Lyuiiuca for example. In the table it will be noted 

 that ilie great majority of the animals represented are pro- 

 ducers or herbivores and detritus eaters. In Lower South 

 Bay these animals feed largely on filamentous algie, their bodies 

 often assuming the peculiar pea green color of the algae. To 

 what extent the carnivorous animals or consumers affect the 

 numbers and the production of the other animals is not known, 

 but that it must be considerable is evident. The animals of 

 herbivorous and detritus feeding habits, on the basis of the 

 number of individuals given in Table No. 38, number about 

 7,743 million. Those of carnivorous habits number about 

 23 million. The herbivorous and detritus feeding animals 

 therefore oiittinniber the carnivoroiis feeding animals about 

 SS7 to one.^ 



In the discussion of the food relations of fish three major 

 divisions of the subject should really be considered. First, 

 the ultimate, or primitive food material, which comprises the 

 chemical elements and compounds such as nitrogen, carbonic 

 acid, phosphoric acid, calcium carbonate, silica, etc., chemicals 

 which are taken up by plant activities (which are synthetic) 

 and converted into the proteids, carbohydrates, and oils of the 

 plant tissues. The ])lants form the second division standing 

 between the chemical compounds which are directly useless 

 to animal life and converting them into digestible material 

 which the animals are able to use. The animals form the third 

 division, and convert the plant tissue into animal proteids, fats, 

 and carbohydrates. These animals then form the food of a 

 majority of fish. It will be seen, therefore, that a study of 

 the food question includes broadly the ])hysical medium sur- 

 rounding the plants, the plants themselves, and the animals 

 using these plants as food. Johnstone's ('08, pp. 189-190) 

 comparison of the "crop of the sea" (plankton) with the 

 crop of the land (hay, grain, potatoes, etc.) and of fish. 



