22 U. S. BUREAU OF FISHERIES. 



EGG MEASUREMENTS. 



For practical fish-cultural purposes the desirability of adopting a 

 standard of measurement for the eggs of such fishes as the whitefish, 

 cisco, yellow perch, pike perch, the marine species, and others that 

 produce eggs of small size in large numbers has long been apparent. 

 Because of these variations in size the standard would be to some ex- 

 tent arbitrary, but if recognized by all fish-culturalists its practical 

 value in keeping uniform records of eggs collected and distributed is 

 evident. 



In making shipment of such eggs from point to point it not infre- 

 quently happens that the eggs are measured by the consignor under 

 one standard, w^hile the consignee uses another. A recognized stand- 

 ard of measure w^ould obviate this confusion. In view of the rather 

 rapid change in the size of the eggs of most fishes after fertilization 

 and during incubation, it is desirable to have one standard measure 

 for eggs in the green stage and another for eyed eggs. 



HATCHING EGGS IN GRAVEL. 



Recently many fish-culturists have become interested in the so- 

 called gravel method of incubating the eggs of salmon and trout. 

 This method, originated, we believe, by Alexander Robertson, a 

 Canadian fish-culturist, consists in placing the fertilized eggs, either 

 green or eyed, in a suitable receptacle between alternate layers of 

 gravel, all of the eggs being completely covered. The receptacle is 

 then so placed as to receive a constant flow of water by seepage 

 through the gravel, the volume not being sufficient to disturb the 

 eggs. 



Experiments conducted along this line at a number of the bureau's 

 stations with eggs of the sockeye and chinook salmons and rainbow 

 and brook trouts have yielded fairly uniform results. The experi- 

 ments have involved placing the eggs in gravel in various kinds of 

 containers, in hatching troughs, in rearing ponds in the open air, 

 and in the beds of creeks. In practically eveiy instance a good per- 

 centage of hatch has been obtained, except in cases where the water 

 circulation was imperfect or where frost had penetrated to the eggs. 

 The former point is illustrated by the following report from the 

 superintendent of the St. Johnsbury (Vt.) station: 



Last winter, 1921, we put 4,000 brook-trout eggs in a box about 1 foot square 

 under the west end of tbe York Pond Duni. Tlie box was set in such a way 

 that the water was forced up through eggs and gravel. There was a con- 

 siderable loss of eggs in the corners of the box, but otherwise they hatched 

 normally. My judgment is that the loss was due to imperfect circulation in 

 the box. 



Observers of the experiments are also very nearly unanimous in 

 the opinion that the fry produced by this means ot incubation are 

 exceptionally virile, are darker in color than f r}'^ hatched by the usual 

 methods, and do not emerge from the gravel until the near approach 

 of the feeding stage. 



It seems hardly probable that the method can be developed to a 

 point where it will be of direct value in hatchery operations or 

 thaf it will replace present methods of incubating the eggs of sal- 

 mon and trout, particularly where such eggs are to be handleci in 



