44 The Food of Fishes. 



MiCROPTERUS SALMOIDES, LaC. Sm ALL-MOUTHED BlACK BASS. 



This species, called also tiger bass, river bass, etc., is 

 the black bass par excellence. It ranges, usually, in deeper 

 and clearer water than the preceding ; but both are often 

 taken together. 



I have made full notes of the food of twenty-seven speci- 

 mens — three adult and the others young. I had none of 

 this species under an inch in length ; but, judging from 

 the general resemblance of the food of this and the pre- 

 ceding bass at later a2;es, I do not doubt that this will also 

 be found to feed at first on Entomostraca, although insect 

 food is possibly more important to it from the beginning. 



Seven individuals, from one to two inches in length, 

 were all taken in July from rocky ripples in the Fox River, 

 at Dayton, 111., a few miles above the mouth of the stream. 

 These had eaten only five per cent, of Entomostraca, — the 

 whole remainder of the food consisting of insects, of which 

 Corixa Uwiida^ young and adult, and larvae of May-flies 

 and darning-needles (Agrionidse) were the most impor- 

 tant kinds. Four per cent, of the larvse of Chironomus are 

 worthy of notice. The scarcity of Entomostraca in the 

 food of fishes as small as these is probably due to the situa- 

 tion in which these specimens occurred, as few Entomos- 

 traca are to be found in swift water. The same fact will 

 account for the presence of Chironomus larvae, — found 

 abundantly under stones in rapid streams. 



The next ten specimens, between two and three inches 

 long, were taken in July, partly at the same place as the 

 preceding, and partly from the Illinois River, a few miles 

 below the mouth of the Fox. These differed from the 

 smaller specimens chiefly in the appearance of fishes in the 

 food (five per cent.) and in the absence of Neuroptera. 

 Probably the last of these differences, at least, was acci- 

 dental. A few larvae of aquatic Coleoptera (Hydrophilidae 

 and Dytiscidae) were noticed. Oorixas, including C. tu- 

 mida^ Uhl, and C. signata^ Fieb.,* amounted to eighty-two 

 per cent, of the food. 



In those ranging from three to four inches in length 

 (seven individuals), the fishes eaten rise to fourteen per 

 cent., but the insects drop away to seven per cent., and 



*Determined by Mr. Uhler. 



