MANUAL OF FISH-CULTURE. 121 



ary, 1897, many of these animals were pumped up witli the water 

 supply of Put-in Bay station. The stomachs of a considerable number 

 of them contained whitefish and cisco eggs, the contents of one stomach 

 being 288 whitefish and 4 cisco eggs. 



Another voracious destroyer of the whitefish is the common yellow 

 jierch {Perca Jlarescens). The deck of a boat has been seen covered 

 with the eggs of the whitefish and cisco pressed out of the stomachs of 

 perch taken from gill nets the last of I^ovember on the reefs, where they 

 had gone to feed on the eggs. 



The vari(ms smaller Cypriniiliv and some other fishes, crawfish, and 

 wild fowl make the eggs of fishes a considerable portion of their diet, 

 those which require the longest period in hatching, of course, suffering 

 most. 



ARTIFICIAL PROPAGATION. 



The artificial propagation of whitefish has long since passed the 

 experimental stage and has attained a high degree of perfection. The 

 work can be carried on with great facility, and its value is especially 

 apparent when it is considered that under natural conditions only 

 a very small percentage of the eggs hatch, while through artificial 

 pro]>agation from 75 to 95 per cent are productive. Practically all the 

 eggs taken for hatching purposes are obtained from fish caught by the 

 commercial fishermen, which would otherwise be lost. 



The methods of culture hereafter referred to are those adopted at 

 the Put-in Bay (Ohio) station, but these do not differ in any essential 

 particular from those in general use. 



In the fiscal year 1895-96 the United States Fish Commission hatched 

 and planted 189,690,000 whitefish fry, and in the subsequent year 

 95,049,000 fry were hatched and liberated in suitable waters. 



HOW THE EGGS ARE TAKEN AND TREATED. 



The taking, impregnating, and handling of the whitefish eggs are 

 simi)le i)rocesses, but require great care at every stage. Eggs are 

 often injured by undue haste in strijDping, and many are lost by allowing 

 them to fall too great a distance into the spawning-pan. Eggs are very 

 delicate when first taken and before the absorption of water has made 

 the investing membrane tense, and if roughly treated will be seen to be 

 ruptured as viewed under the microscope. With care about four fifths 

 of the eggs wdl hatch. Improjjer attention to the impregnating process 

 may also result in serious loss of eggs. While scarcity of milt may 

 lead to the nonfertilization of the eggs, the manner in which the milt is 

 brought m contact with eggs is a more common cause of failure. 



The eggs sup](lied by each spawn-taker should be examined daily, 

 and if it is found that a considerable number have ruptured yolks it may 

 be taken for granted that the spawn-taker has handled the fish and eggs 

 roughly, and if many are unimpregnated it is evident that he did not 

 use sufficient milt or that it was not properly applied to the eggs. 



