FISH-CULTURAL PRACTICES IN THE BUREAU OF FISHERIES. 741 



particular station may run 250 to the fluid ounce during the height of the season, 

 while the first take may have run 300 to the ounce and the last eggs of the 

 season may average 400 or more to the ounce. These variations make it neces- 

 sary frequently to establish a new measure for ascertaining the actual number 

 of eggs. There is also to be taken into consideration the fact that eggs of 

 almost all fishes increase in size from 4 per cent to 1 5 per cent according to the 

 species, from the time they are water-hardened up to the time they are about 

 to hatch. 



This fact, coupled with the fact that eggs of the same species vary in size 

 at diff'erent sources of supply and periodically at the same source of supply, is 

 a point in favor of the von Bayer method of computing the numbers of eggs of 

 small diameter. 



Sac-absorbed fry and advanced fry of the trouts, landlocked salmon, etc., 

 may be measured in the same manner as are the eggs — in an apothecary's grad- 

 uate or other container, straight vertical sides being preferable to the flaring 

 sides of the ordinary glass graduate. The ordinary graduated half pint or pint 

 cup used by cooks is a very convenient measure. The fry are poured in until 

 the measure is overflowing with them to the exclusion of practically all the water, 

 the filling and emptying being done quickly. Actual count of the number in 

 one measure establishes the basis for computation. The growth during this 

 period being very rapid, however, a new unit must be determined daily. 



The numbers of fingerlings are ascertained by actual count of each lot as 

 dipped a few at a time from trough to transportation can or other receptacle 

 by means of a small hand net of tightly stretched bobbinet. 



TRANSPORTATION OF EGGS. 



To equalize and facilitate the work of the hatcheries it is customary to 

 transport, sometimes to considerable distances, both green and eyed eggs from 

 one station to another, thus effecting the distribution of fish through the dis- 

 tribution of eggs. Several auxiliary stations are maintained on the Great Lakes 

 solely for hatching eggs received from Northville, it having been found economy 

 to transfer to them as eyed eggs the portion of the Northville station output des- 

 tined for distribution to waters in those localities. Both green and eyed eggs 

 are also shipped to state hatcheries and the latter to foreign countries. 



The methods of conveying green eggs from the field where collected vary 

 to suit conditions. The stations at which eggs of commercial fishes are hatched 

 in large numbers are usually located conveniently to the source of supply so 

 that it is possible to carry the freshly fertilized eggs to them in the pans, buckets, 

 or other receptacles which constitute the equipment of the spawn taker. It 

 often happens, however, that the eggs must be held in the field or be in transit 

 for two or more days, and in such cases a packing case is employed. 



