740 BULLETIN OF THE BUREAU OF FISHERIES. 



Unless the eggs are to be transferred to a hatchery beyond the jurisdiction 

 of the shipper, the eggs may not be measured vmtil a more convenient time, it 

 being possible from long familiarity with the capacity of the apparatus in actual 

 use to estimate quite accurately the number of eggs on hand at any time. Pro- 

 viding they are spread uniformly, the number of eggs to a square inch is a fairly 

 accurate basis for ascertaining how many eggs are on each tray. Some fish 

 cultvu-ists prefer to ascertain the actual number of eggs on hand by weighing 

 them after having determined by actual count the basis for such calculations. 



These methods are especially applicable to the heavy eggs of the Salmonidae, 

 and may be employed not only after water hardening but also at any stage of 

 incubation after the eggs are eyed up to a day or so before hatching, at which 

 last stage a measurement closely approximates the number of fry that will be 

 in the subsequent hatch. 



Eggs hatched in jars are usually measured by means of a graduated scale 

 in the form of a square made of wood, the units indicated on the long leg of the 

 square. The square is adjusted to the jar as shown in figure i . The scale reads 

 from the bottom line upward, the first or bottom line being at a height corre- 

 sponding to the level attained in a jar by a measured half pint of water, and 

 each line represents the number of eggs of a given species as established by actual 

 count from a measured half pint. The dead eggs will have been from time to 

 time siphoned off and when the remainder are fully developed or about to hatch 

 the scale is applied to each jar and a very careful measurement is made to ascer- 

 tain their number. The number of fry available for distribution will be approxi- 

 mately the number of eyed eggs in the jars just before hatching, as the mortality 

 after this stage of development is usually inappreciable. 



A novel method of obtaining the number of eggs in a given lot has lately 

 come into use, and as the work can be done without counting a large number 

 of eggs, has proved especially valuable in dealing with eggs of small size at field 

 stations where no measurements have been established. This method, devised 

 by Mr. H. von Bayer, architect and engineer of the Bureau, employs a gauge 

 which quickly gives the diameter of the eggs, knowing which it is possible by 

 reference to a diagram to determine at once the number of eggs to the quart." 



In the keeping of accurate hatching records it is important that the basis 

 for computations be ascertained immediately before any general measuring 

 methods are applied because it is well recognized that eggs of most species vary 

 in diameter with stock from different waters and that eggs from any given col- 

 lecting station vary at different periods of the spawning season, those taken at 

 the height of the season being larger and more uniform than those taken earlier 

 or toward the close of the season. For instance, brook trout eggs taken at a 



" von Bayer, H. : A method of measuring fish eggs Proceedings Fourth International Fishery 

 Congress, Bulletin of the Bureau of Fisheries, vol. xxviii, 1908, p. 1009-1014. 



