HABITS OF YELLOW PERCH. 313 
PLANTS (5.5), all year: PLANts—Continued. 
Unidentified remains (4), 225, all year. Alge, all year—Continued. 
Alga, all year— Spirogyra, 1, November. 
Unidentified, 7, April to September. Tabellaria, 1, November. 
Aphanothece, 19, April, September. Ceratophyllum, 1, January. 
Chara, 2, March, April. Elodea, 5, March, September. 
Closterium, 1, April. Lemna, 8, May to December. 
Desmids, 1, April. Plant leaves, 7, May to July. 
Diatoms, 20, October to March. Plant seeds, 12, May to March. 
Filamentous alge, 121, all year. Potamogeton, 3, May to October. 
Gelatinous alge, 4, July. Vallisneria, 1, October. 
Hydrodiction, 1, July. Wolffia, 2, June. 
Protococcus, 5, January, April. CaCO, CRYSTALS, 17, February to April.¢ 
Rivularia, 3, October. SILT AND DEBRIS (6.1), 276, all year. 
QUANTITY OF FOOD CONSUMED AND RATE OF DIGESTION. 
After the constituents of perch food had been ascertained and their percentages by 
volume determined, it became necessary, in order to gain some idea of a perch’s food 
requirements from day to day, to find out how much it could consume in a given time 
and how fast digestion progressed. With such purposes in mind, a medium-sized perch 
(weight, 48 g.; volume, 50 c. c.) was placed in a 5-gallon spherical glass aquarium and 
fed all it would eat from June 19 to July 20, 1916. The results of these experiments 
are shown in Table 13. Similar experiments were carried out later on smaller and 
larger fish and are in part summarized in Tables 11 to 15. The largest perch under 
observation were three individuals weighing about 247 g. and having volumes of about 
250c.c. They were tested from December 18, 1916 to January 23, 1917, and ate only 
a few Dikerogammarus, although they were offered the same foods as smaller fishes 
tested at the same time (Tables 12 and 14). This agrees with the observations of 
Knauthe (1907), who stated that large carp usually would not eat when the temperature 
was below 6 to 8° C. 
As to the volume of the food in proportion to the bulk of the perch eating it, we 
have only a few observations. Table 13 shows that a perch displacing 50 c. c. of water 
ate the following percentages of its own volume per hour when given more than it 
consumed: Damselfly nymphs, 0.3 per cent; snails, 0; minnows, 0.46 per cent; earth- 
worms, 0.32 per cent. On January 12, 1917, a perch having a volume of 2.1 c. c. atea 
minnow (Pimephales notatus) which had a bulk of about 0.7 c. c. Reighard (1915, 
Pp. 237) gives instances where adult perch ate other individuals of their own species 
which were almost as large as themselves. 
The tables show that the same foods were digested more rapidly by small than by 
large perch and that, when fish of similar size ate at different temperatures, digestion was 
slower at lower temperatures. To take a concrete illustration: A perch about 62 mm. 
long ate seven chironomid larve (having a volume of 0.3 c. c.) at 2.5° C. and digested 
them in 43.7 hours; the same individual at 16° C. ate 0.84 c. c. of chironomid larve and 
digested them in 22 hours. A perch measuring 30 c. c. in volume ate 78 chironomid 
larve (having a volume of 4.2 c. c.), digesting them in 46.5 hours at 2.5° C. At 24° C. 
this perch ate 26 damselfly nymphs (no chironomid larve were available) having a volume 
aQn Nov. 23, 1917, calcium carbonate crystals were found in one of three perch caught at a depth of 2.5 m. in Lake Mendota. 
