780 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [10] 



It was a curious fact, however, that when the water was drawn off at 

 the eud of the experiment, more than half the Entomostraca were 

 Limnocalanus ; a fact parlly to be explained by the predaceous habit 

 of the latter, and partly by the facts relating to the food of the fishes 

 themselves, which are presently to be detailed. 



The fry were placed in the tank and supplied with their first food on 

 the evening of the 12th of March. On the 14th, one hundred specimens 

 were removed, and twenty-seven of these were dissected. Twenty 

 were empty, but the remaining seven had already taken food, all Cyclops 

 or Diaptomus. Three had eaten Cyclops only, and six Diaptomus, 

 while two had eaten both. Fourteen of these Entomostraca, seven of 

 each genus, were taken by these seven fishes. From those captured 

 the next day, twenty five specimens were examined, of which nineteen 

 were without food. Of the remaining six, three had eaten Diaptomus 

 and three Cyclops ; five of the former being taken in all, and ten of the 

 latter. Three specimens were next examined from those caught on the 

 19th of March, two of which had devoured Diaptomns and a third a 

 single Cyclops thomasi and a shelled rotifer, Anurcea striata. The 

 chaiacter of the food at these earliest stages was so well settled by 

 these observations that 1 deemed it unnecessary to examine the subse- 

 quent lots in detail, but passed at once to the specimens taken on the 

 23d. Twenty-six of these were examined, and found to have eaten 

 thirty three individuals of Cyclops thomasi, fourteen of Diaptomus sicilis, 

 and fourteen of the minute rotifer already mentioned {Anurwa striata). 

 Two had taken a few diatoms {Bacillaria), and one had eaten a filament 

 of an Alga. Cyclops was found in sixteen of the specimens, Diaptomus 

 in nine, and Anuria in eight, only two of them being empty. The 

 amount of food now taken by individual fishes was mnch greater than 

 before, one specimen dissected having eaten two Cyclops and six 

 Diaptomus sicilis, male and female. Another had taken five Cyclops, 

 one Diaptomus, and five examples of Anurwa striata. Still another 

 had eaten four of the Cyclops, four Diapotomus, and one Anuraea. 



Twenty five specimens were examined from those removed on the 

 24th of the month, at which time the water of the tank was drawn 

 off and all the remaining fishes bottled. Four of these had not eaten, 

 but the twenty-one others had devoured fifty specimens of Diaptomus 

 sicilis, forty-seven of Cyclops thomasi, fourteen of Anurcea .striata and a 

 single Daphnia hyalina, the latter being the largest object eaten by any 

 of the fishes. A few examples of their capacity may well be given. 

 The ninth example had eaten six Diaptomus, two Cyclops thomasi, and 

 one Anuria ; the tenth had taken eight Diaptomus, two Cjxlops, and 

 an Anuria ; and the twentieth, seven Diaptomus and three Cyclops 

 thomasi. In two of these examples w^ere small clusters of orange glob- 

 ules, probably representing unicellular Algse. 



Summarizing these data briefly, we find that of the 106 specimens 

 dissected sixty-three had taken food, and that the ratio of those which 



