Present in small numbers in the plankton of 5 of the 

 marginal stations, 4 of which were on the American 

 shore and outside of the lake itself. It is eaten by 

 small carp. 



12. Cyclops (Eucyclops) pr asinus (Fischer). Found 

 at 4 of the marginal stations including Rondeau Harbor, 

 Point Pelee and Sandusky Bay. It has not been found 

 in the stomach contents of any of the small fish of the 

 lake, but doubtless serves as food for some of them. 



It is stated by Marsh (1895) to be a limnetic form and 

 common in the Great Lakes and hence is of some value 

 as fish food. 



13. Cyclops robustus G. O. Sars. Present in the 

 plankton of 12 marginal stations and in 22 stations of 

 the linoral and lacustric zones, most abundant in the 

 littoral zone and along the American shore. This is a 

 true bottom form and all the specimens with few ex - 

 ceptions were taken in the bottom net or in the Helgo - 

 land trawl. It is eaten by the carp and carp sucker, 

 and on account of its large size and abundance it makes 

 an important contribution to the fish food of the lake. 



14. Cyclop s serrulatus Fischer: Eucyclops agilis 

 (Koch). Found at every station in the marginal zone, 

 and rated as abundant at 12 of them; thus far it has not 

 appeared in either of the other two zones. It has been 

 obtained in the stomach contents of the bullhead, 

 straw-colored minnow, Cayuga shiner, redhorse sucker, 

 carp, and stoneroller. As it is more restless than most 

 of the other species and is constantly darting about, it 

 probably contributes more often to the food of hungry 

 fish. 



15. Cy c lops viridis (Jurine): Cyclops vulgaris 

 Koch. Present at 13 of the marginal stations but not 

 found in either of the other two zones. The fact that 



it was washed out of the mud at 1 or 2 stations indicates 

 that it frequents the bottom, and in European lakes it 

 has been known to descend to rather considerable depths. 

 It has been identified in the stomach contents of the 

 redhorse sucker, whitenosed sucker, carp sucker, white 

 sucker, carp, bullhead, straw-colored minnow, trout - 

 perch, white bass, and yellow perch. Its large size 

 and its habit of burrowing in the mud doubtless contri- 

 bute to its being eaten by so many small fish, espe - 

 cially the suckers. 



near the 20 -meter line. It is one of the smaller spe- 

 cies of the genus, but its great abundance more than 

 makes up for its inferior size. Its breeding season 

 must come in April or the first of May for its numbers 

 were at their maximum early in June during the first 

 trip for collecting plankton. Its percentages of the 

 macroplankton diminished a little in July and August 

 and increased again in September, but the diminution 

 was largely due to a rapid increase in the cladocerans 

 rather than to a decrease in the copepods. Another 

 breeding toward the end of July and the beginning of 

 August carried the percentages up again, and because 

 the cladocerans were increasing at the same time the 

 rise in the copepods was really greater than it appeared 

 to be. A comparison of the surface and bottom tows 

 shows that this species is an active migrant; when its 

 percentage was large in the surface net it was at the 

 same time smaU in the bottom net and vice versa. At 

 the eastern end of the lake in 1928 this copepod was 

 most abundant in the surface samples along the Amer- 

 ican shore and in the bottom samples along the Can- * 

 adian shore. In 1929 during June and July it was more 

 abundant at the surface in the eastern half of the lake 

 and at the bottom in the western half of the lake, and 

 there was a marked contrast between the two. During 

 August and September this relationship was reversed in 

 both halves, but at the same time the contrast between 

 the two became so much less that it almost disappeared. 

 The species was then universally distributed over the 

 entire lake and in all 3 zones, and the percentages at 

 the surface and bottom were often exactly the same. 

 This would suggest that the vertical migration, which is 

 very much in evidence during June and July, diminishes 

 later in the season and practically disappears in many 

 places. This copepod has been identified in the stomach 

 contents of the silverside and Cayuga shiners, and is 

 probably an important food in the deeper parts of the 

 lake for the small fish there, very few of which have 

 thus far been examined for food contents. 



17. Diaptomus minutus Lilljeborg. Found at a 

 few stations in the marginal and littoral zones, but not 

 appearing at all in the lacustric zone. It is the small- 

 est species of the genus and this combined with its 

 scarcity gives it practically no economic value as fish 

 food. It has not yet been identified in the stomach con- 

 tents of any of the lake fish, but is probably eaten by 

 some of the smaller ones. 



16. Diaptomus ashlandi Marsh. Present in all 3 

 lake zones but most abundant in the lacustric zone 



18. Diaptomus ocegonensis Lilljeborg. Present in 

 the plankton of 14 of the marginal stations and rarely 



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