FISHES OF DOUGLAS LAKE, MICHIGAN 237 



midsummer perch of less than 2.26 inches are found on the shoals, those between 4 and 6 

 inches in the vegetation, and those of 7 inches or more in deeper water. 



Nineteen of the perch in our table showed recognizable stomach contents. Of 

 these, 1 1 contained insects only, i contained insects together with a crayfish, 3 contained 

 crayfish only, and 4 contained fish only. The relative importance of the three kinds of 

 food is perhaps indicated by the frequency of the occurrence of each, which is the ratio: 

 Insects 3, fish i, crayfish i. 



The largest perch in our record is 8.4 inches. They appear to be exceptionally 

 slender, for while in systematic descriptions the depth is given as contained 3.3 to 3.8 

 times in the length, the depth in Douglas Lake specimens is contained about 4.3 times in 

 the length. Forbes and Richardson (1908) say "the species may reach the length of a 

 foot and a weight of more than 2 pounds, but does not commonly weigh much more than 

 a pound." The heaviest Douglas Lake specimen weighed but 7 ounces. There are no 

 data from other lakes for comparison with those from Douglas Lake, but Douglas Lake 

 specimens strike one as being slender, short, and under weight. 



After storms perch are found dead on the beach in great numbers. Protruding 

 from the mouth of such a one is often seen the head of another that has been swallowed 

 tail first. When pulled out the swallowed perch is, in many cases, found to be almost as 

 large as that from which it was drawn, and is without doubt the cause of its death. 

 Cannibalism of this sort is common in the writer's experience among young wall-eyed 

 pike kept in confinement and insufficiently fed. It indicates starvation. The small 

 size of the Douglas Lake perch, the high midsummer mortality, and the occurrence of 

 the sort of cannibalism described, indicate that the conditions in the lake are not the 

 most favorable for perch. 



In August and September schools of young perch are conspicuous on the sand shoals 

 of South Fishtail Bay and doubtless on the other shoals. One of these was seined, and 

 of the 475 individuals captured 203 were found to be young perch from 1.85 to 2.25 

 inches long. The remainder of the school was made up of 267 spot-tailed minnows and 

 5 suckers of about the same length as the perch. The young perch are readily distin- 

 guished in the water from the other species in the school by the seven bars on the sides, 

 which are more pronounced than is usual with larger perch. They have also a well- 

 defined black, basal spot at the caudal margin of the first dorsal, which has a more pro- 

 nounced black border than in the adult. 



Placed in an aquarium, the young fish may be seen to feed on plankton. When 

 the fish are placed in formalin immediately after capture, twisted cords of brown fecal 

 matter are soon found hanging from the vent. These have on the surface a smooth 

 coherent pellicle consisting apparently of granular mucus. Under the needle the cord 

 breaks readily into ovoid masses of equal size each of which is seen to consist, within the 

 pellicle, of many tests of microcrustacea. The most numerous individuals were those 

 of a ChydorusAike cladoceran, but Simocephalus and Daphnia were also present in num- 

 bers and there were a few copepods. These fecal cords varied in length from yi inch to 

 yi inch. By counting the number of tests in one of the 40 ovoid masses into which a fl- 

 inch piece broke, the number in the whole piece was estimated at 800. There were no 

 remains of insect larvae. The 203 young perch had thus consumed about 162,400 Crus- 

 tacea, whose remains were found in the fecal cord. The stomach and intestine of one 

 19371°— vol 33—15 16 



