FISHES OF DOUGLAS LAKE, MICHIGAN. 



223 



are usually the depths at which gill and fyke nets were set on the bottom. Lengths of 

 fishes do not include the caudal fin. 



Leucichthys artedi (Le Sueur), lake herring, or cisco. — This species has not been 

 taken in nets, but adult specimens are frequently cast up on the beach of South Fishtail 

 Bay. Three of them measured 5, 6>^, and 7 inches, respectively, the latter a male with 

 slender white testes }i inch broad. A male 6J4 inches long and with large testes was 

 picked up, still living, over deep water in South Fishtail Bay, September 18, 191 1. Our 

 small-meshed gill net has taken suckers of 7 or 8 inches when set on the bottom in water 

 of 26 and of 42 feet depth. It should have taken lake herring if they had been present 

 there. In midsummer the same net has taken no fish when set on the bottom in water 

 deeper than 45 feet, although in September a single sucker was taken at 72 feet. The 

 absence of oxygen in the bottom water below 45 feet in midsummer makes it impossible for 

 fish to live there. The lake herring must therefore live in deep water at some distance 

 above the bottom. Perhaps its habitat will be found in the neighborhood of the ther- 

 mocline. This species is characteristic of the Great Lakes, where its average length is 

 12 inches. Our largest specimens are only 7 inches long. 



Catostomus commERSONII (Lac^pede), common sucker. — The records in table I 

 show the suckers taken in 191 2. 



Table I. — Records of Catostomus commersonh Taken in Douglas Lake in 1912. 



Common suckers have been seined in Maple River and have been seen at the mouth 

 of Bessie Creek. There can be no doubt, then, that they occur over the whole lake and 

 are amongst its commoner fishes. They are found in all the habitats. On September 

 23, 191 1, one was taken in a gill net drawn from a depth of 72 feet. In July and August 

 suckers have not been taken below the depth of 43 feet. They are sometimes seen 

 feeding on the sand shoals in water a foot or two deep. They may therefore occur at 

 any depth in the lake, but are not known below the thermocline in midsummer. 



Food. — The young of this species are seen on the sand shoals in July and August 

 in company with the young of the yellow perch and the spot-tailed minnow. In a school 

 of 475 of these young fish taken on September i , 1 9 1 1 , five were suckers between 1 K" and 

 2 inches long. The alimentary canal, from cesophagus to anus, of an individual 2 inches 

 long was found to measure 3 inches. Its contents formed a brown mass inclosed in a 

 mucus pellicle. The whole of it could be easily stripped from the canal. The contents 



