ARTIFICIAL, PROPAGATION^ OF WHITEFISH, ETC. 9 



approxim;i*^ely 5 quarts per minute at tlie beginning of incubation, 

 which amount is reduced to 4 quarts later on. Tliis water supplies 

 in turn the succeeding rows of jars in the battery. For this reason 

 the jars on the upper row should never be removed without making 

 l^rovision to supply those below. 



In a mean water temperature of 35° F. the eye spots of the fish 

 are visible to the unaided eye in about 40 days, and the entire incu- 

 bation period averages 133 days. The food sac is absorbed in from 

 5 to 10 days after the fry have hatched, the time varying somewhat 

 with the period of incubation. 



The microscope is a great aid in whitefish culture, enabling the 

 operator to determine the exact percentage of dead eggs and, to a 

 great extent, the cause of their loss, allowing him to remedy some if 

 not all of the evils. For examining eggs in their early stages the 

 microscope is placed horizontally, the eggs being held in a cell filled 

 with water. This may be made easily by fastening two ordinary 

 glass slides to a strip of wood one-eighth of an incli thick, with a 

 portion cut away to form a receptacle for the eggs. The wood is 

 thoroughly saturated with asphaltum varnish, and after drying the 

 sides should receive a thin coat, the sides being laid on and placed 

 under pressure to dry. "V^Tien dry, an additional coat to the outer 

 joints of contact will guard against possible leaks. Such cells are 

 not satisfactory and a good examination of the eggs can not be made 

 with them. Most optical houses are able to supply what is known as 

 " watch crystals " that are made especially for this purpose. 



If the egg be examined six to eight hours after being fertilized, the 

 germinal disk will be found to have contracted to a saucer-shaped 

 cap, extending over about one-fifth the surface of the yolk. It is 

 sDiooth and even, gradually thinning to a sharp outer rim, with a 

 thickness of about one-fifth its diameter in the center of the cap. 

 Segmentation not having commenced at this stage, the impregnated 

 eggs can not be distinguished from the unimpregnated ones. At 18 

 hours segmentation will be well advanced and the disk will have con- 

 tracted into six or eight rounded nodules of uneven size, with well 

 defined valleys between, the sharp rim having disappeared. At 24 

 hours, which is the best time to determine the percentage of live eggs, 

 the disk will present a somewhat similar appearance except that it 

 will be divided into 25 or more segments, easily seen under the glass. 

 The disk of tlie unimpregnated egg of the same age forms an almost 

 exact hemisphere, is perfectly smooth in appearance, and is therefore 

 easily distinguishable from a live egg. Segmentation now proceeds 

 rapidly, and at 72 hours the cell looks about the size of a mustard 

 seed under a 1-inch objective, the most suitable power to use in this 

 work. 



During the entire period of incubation, but more especially in its 

 early stages, the eggs should be worked as gently as possible, only 

 enough water being used to give them sufficient motion to prevent 

 "banking." Just at the commencement of incubation they require 

 about 5 quarts of water to the jar per minute, but later they can be 

 run with a quart less per minute. For the first week or more the eggs 

 require constant watching, and although the whitefish egg is not con- 

 sidered adhesive, agglutination will ocasionally occur when the water 

 becomes roily, and unless the banks thus formed are separated by 

 gentle stirring with a feather (the long feathers of a turkey wing are 



