FISH-CULTURAL PRACTICES IN THE BUREAU OF FISHERIES. 705 



tube, with which a few at a time may readily be removed from the jars, it is 

 usually possible to distinguish the live eggs at any stage of development. 



The eggs average 29 to the linear inch when first expelled and 28 to the 

 inch after being water hardened. They are usually measured into the jars 

 with a I -quart apothecary's graduate, and are computed at 1,600,000 to the 

 quart. 



To guard against the escape of very small fry from the receiving aquarium 

 the usual waste water outlet is closed, and the water is carried off by means of 

 one or more siphons, the suction ends being provided with wire cages covered 

 with two or three thicknesses of cheese cloth. To regulate the level of the 

 water in the receiving tank the outlet ends of the siphons empty into an adjacent 

 receptacle, usually a hatching jar, the rim of which is at the desired water level. 



YELLOW PERCH. 



It is feasible, and under some conditions desirable, to expel and fertilize 

 yellow perch eggs artificially, but under proper conditions practically all natu- 

 rally deposited eggs are fertilized. For this reason the Bureau's work largely 

 consists in the incubation of the natiu-ally deposited eggs obtained from fish 

 confined in crates for the purpose, and to some extent by collection of natural 

 spawn in marshes where left by receding waters. 



It has been found that the eggs can be hatched in almost any kind of con- 

 tainer through which water is flowing — open troughs, open jars, shad aquaria, 

 etc. — but careful experiments indicate that the McDonald open-top and the 

 Downing jar are preferable to other kinds of equipment, the Downing jar pos- 

 sessing the advantage of greater capacity. It will hold 130,000 to 150,000 

 eggs, and when thus incubated the eggs are subjected to a water circulation of 

 about I pint per minute. 



As little has been published on the methods of culture of this fish, the data 

 of the superintendent in charge of the yellow perch operations at Bryans Point, 

 Md., will be given in some detail: 



Here the fish are purchased from commercial fishermen, are held in crates 

 having comparatively tight bottoms, and allowed to spawn naturally. The 

 crates are 8 feet long, 4 feet wide, and 2>2 to 3 feet deep, and are placed in the 

 mouth of a small creek tributary to the Potomac reached by tide water from 

 the river. A small number of fish are also kept in a large tank at the hatchery, 

 through which there is a constant flow of river water in connection with the 

 regular station supply. 



The collecting of fish begins about the middle of March or when the water 

 temperature ranges from 34° to 37°. The water temperature in which spawn- 

 ing occurs ranges from 42° to 46°. In 1908 the first eggs were obtained March 



