Fish Food 85 



D. ECONOMIC STUDIES 



Study 20 

 THE FISH-FORAGE OF A WATER MEADOW 



IVIaterials for this study and for Study 21 should be collected at the same time and place 

 this, to show what is present; that, to show what is selected by the fishes. 



Apparatus needed: Hedges shears, hand screens, pails, white lined dishes and lifters. 



Work Program: 



1. Gathering with a seine the small fishes (to be used in Study 21) and other larger 



active animals present. 



2. Individual examination of }4. square meter of the weed bed* and count of its ani- 



mal population. 



3. Sieve net examination of the bottom mud under some of the sample plats. 



4. Reading in text, Life of Inland Waters, pp. 377 to 400. 



For Record include: 



1. A diagram of a vertical section of a bit of the weed bed showing stratification and 



naming the principal plant and animals in each stratum. 



2. A count of the animals present t in the ^ square meter individually counted. List 



them by groups. Underscore carnivores in red and herbivores in green. 



Study 21 

 A STUDY OF FISH FOOD 



IVIaterials for this study should be obtained along with those for the preceding one. 



Work Program: 



1. A laboratory examination of the contents of the alimentary tract of a number of 



young fishes to determine what they have eaten. 



2. Reading in Life of Inla^id Waters, Chapter VII. 



For Record include: 



1. The names and lengths and dates of capture of the specimens examined. 



2. A table of the foods identified, showing separately for each species, and for each 



large difference in size and age, the following: 



I. Plants eaten — state and condition, percentages of algae and fragments of higher 



plants. 



II. animals — numbers and percentages. 



Other fishes. 



Herbivorous invertebrates, naming kinds as far as possible. 



Carnivorous invertebrates, naming kinds as far as possible. 



* Obtain, from an undisturbed part of the weed bed, Elodea, Potamogeton or other dense-growing submerged 

 water weeds by shearing off the weeds at sides and at level of bottom mud with hedge shears, quickly lifting 

 the loosened mass on a hand screen shoved beneath it, and dumping in a pail for subsequent division and ex- 

 amination in the white lined dishes. 



t Only such of the animals as are large enough to be taken up with the Hfter need be counted. Counts should 

 be careful enough to give an accurate idea of relative abundance. If counts of entire class are averaged the 

 result will be more accurate. Do not overlook the tube-dwelling midge larvae. 



