FISH FAUNA OF DOUGLAS LAKE REGION. 35 



In lookino; for tho causes of death of the (ish listed in Table 9, 

 the following are at least to be considered: (1) mechanical injury, 

 (2) injury through attacks of other species, (3) the beaching of in- 

 dividuals while pursuing or swallowing prey, (4) accidental beaching 

 while attempting to escape enemies, (5) disease and parasites. 



The total number of intlividuals of all species showing definite ex- 

 ternal injuries was low, something less than one-tenth of one per cent, 

 and as may be seen in Table 9 these were distributed rather evenl>' 

 among the several species in proportion to the total number beached. 

 Many apparently normal fish, free from parasites and without any 

 sign of injury, were beached which may have been killed by wave 

 action either well out in the lake or at the edge of the shoal water where 

 the high waves break. 



Few if any specimens showed unmistakable injuries due to the at- 

 tacks of other species. A few suckers bore circular wounds resembling 

 lamprey marks but these wounds were of such a nature that they 

 might have been due to any of several other causes. 



In the "beached while feeding" column only those individuals were 

 listed which were found with prey in the mouth. Perca flavescens was 

 the heaviest loser in this w^ay. Seventy-one beached specimens of this 

 species had half-swallowed individuals of Percopsis guttatus in their 

 mouths, and the Percopsidae in almost every case were adults. In 

 addition to the specimens taken with prey in the mouth undoubtedly 

 other individuals are beached while pursuing prey. Catostomus com- 

 mersonii, a bottom feeder, is known to come into shallow water at night 

 while feeding and individuals of this species might easily \)o beached ))>• 

 a sudden storm. 



The beaching of small fishes while attempting to escape larger jnir- 

 suing fishes was on more than one occasion observed. The young 

 suckers, Notropi, and other young fishes are constantly preyed upon by 

 the larger carnivorous species and schools of tiie small fish are often 

 forced to the shore" line by the pursuers. Here an incoming wa\-e 

 completes the beaching. 



Parasites certainly play an important part in the death of a large 

 number of the individuals reaching the l)each. With very few ex- 

 ceptions all of the Cenlmrchidae l)eached, i. e. Ainbloplites nipestr.is, 

 Lepomis pallidus and Eupowoti)^ yibbosus were infected in the gill 

 chambers with parasitic Copepods. Often this infection was very 

 heavy although some specimens bore but a few of the gill patasites. 

 Many suckers and Cyprinids contained worm cysts in the body wall 

 and in the skin. The parasitic worms were not examined, but Or. 

 La Rue (see report of the Director of the Biological Station for 1912) 

 reports a variety of forms and a hca\"\' infi'ction of s(>veral sp(>cies ot f sh. 



