HABITS OF YELLOW PERCH. 335 
Thirty-nine individuals collected on July 17 and August 8, 1916, in Oconomowoe Lake (length— 
maximum, 98; minimum, 35; average, 55.1 mm.),showed: Tail, 25-53-1.3; fins, 24—79-2; head, 26-98-2.5; 
ventral region, 31-132-3.3; dorsal region, 25-123-3. 1; whole body, 38-490-12.9. 
(?) Allocreadium, isoporum Looss,—One specimen, which is apparently referable to this species, 
was found in the intestine of a perch collected in Oconomowoc Lake, August 14, 1916. 
Crepidostomum cornutum (Osborn).—Eight specimens were found in a perch caught in Lake Men- 
dota at a depth of 18 m., January ro, ror8. 
ACANTHOCEPHALA. 
Neechinorhynchus cylindratus (Van Cleave).—This was the common acanthocephalan found in perch. 
Sometimes it occurred in great numbers. In one instance a couple of hundred were found in the 
intestine of a single perch. 
Echinorhynchus thecatus Linton.—One specimen, which is apparently referable to this species, was 
saved from a perch 60 mm. long caught on August 24, 1916, in a minnow seine east of Picnic Point. 
NEMATODA. 
Dacnitoides cotylophora Ward.—Specimens of the nematodes from perch intestines were probably 
of this species. 
HIRUDINEA. 
Piscicola punctata (Verrill).—This was the species of leech usually found on the perch in the lakes 
investigated. 
Placobdella parasitica (Say),—One individual of this species was found attached to a perch caught 
in Lake Wingra October 28, 1916. Our thanks are due to Prof. J. P. Moore, who identified it. 
INSECTA. 
Psephenus sp.—On July 22, 1916, a perch, caught at a depth of 15 m .in Lake Mendota, had a- 
“water penny’’ attached to its body just behind the right pectoral fin. This beetle larva must, there 
fore, be recorded as an accidental commensal or parasite. 
GENERAL DISCUSSION AND CONCLUSIONS. 
The investigations on the perch in the two lakes selected for study have been 
described, and it is now time to return to the problems it was hoped they would solve: 
(1) To account for the abundance of perch compared to other species of fish; (2) to 
determine why perch have a particular maximum size in certain lakes and why they 
are larger in some lakes than in others; and (3) what effect stagnation has on the 
activities of fishes. 
The perch appears to be more abundant than other species of fish because it is 
versatile and not too specialized. Though it has certain specificities of behavior, such 
as the habit of usually feeding on or near the bottom, it is able, more than any other 
fish with which it is associated, to invade all habitats. It may feed on the enormous 
quantities of plankton in the pelagic regions; it is at home among aquatic vegetation; 
and it may grub out the animals embedded in such great numbers in the soft bottom mud 
or even largely subsist for a time on the mud itself. Its chief advantage over the 
common shore’ fishes is in its ability to forsake the shore, with its stores of food 
dependent chiefly on the aquatic vegetation, and invade the depths of the lakes, where 
the chief source of food is the soft sedimentary bottom deposits rich in organic 
constituents. 
The perch has rivals in each of the habitats where it seeks food, but it is an able 
competitor of them all. In shallow waters it may capture mollusca as well as the 
pumpkinseed, littoral plankton as well as the silversides or bream, insects and their 
