8o8 BULLETIN OF THE BUREAU OF FISHERIES. 



It has five transverse pins, resting on the free edges of the boxes, and is weighted 

 sufficiently at K to keep the boxes down in the water. On the contrary, when 

 the rod is raised the boxes will float up. The movement of the rod is brought 

 about by an eccentric (fig. 2, pi. c i ) , which revolves about twice in a minute and is 

 so arranged that the rise of the rod is slow, while the drop is sudden. This 

 up-and-down movement of the free end of the incubators will make the 

 current irregular, break up the eddies, and keep the eggs in continual motion. 

 The eccentric wheel is driven by a waterwheel that utilizes the outflow water 

 from the egg collector described above. 



Hatching. — The usual quantity of cod eggs put into each of the small boxes 

 is i}4 liters, equal to 675,000. The quantity may be raised to 2 liters, but this 

 is rather too much if the specific gravity of the water is low, which very often is the 

 case on this coast. To avoid difficulties in this respect, the water for the hatch- 

 ing boxes is never taken direct from the pumps but from the large pond, which 

 is used as a reservoir and has its overflow pipe placed in its lower part. A tem- 

 porary fall in the salinity of the water in the sea, even for several days, will by 

 this arrangement hardly be felt. About three days after the eggs have been 

 placed in the incubators, the dead ones will have fallen to the bottom and a 

 cleaning out becomes necessary. This will have to be repeated at intervals as 

 may be required and is easily done, as the incubators can be unshackled in a 

 moment and the eggs are very hardy, so no great care is needed. 



When the eggs begin to hatch, the incubators will have to be watched more 

 closely, as the empty shells are apt to fall to the bottom and clog the netting, 

 and a cleaning every day then becomes necessary. At this period great care is 

 needed, as the fry are very tender. The number of days required for hatching 

 the eggs varies according to temperature; at 3° C. to 4° C. the fry will be out in 

 twenty to twenty-five days. The loss in the apparatus during hatching depends 

 very much on the specific gravity of the water, and on the whole the net output 

 of fry will vary between 60 and 65 per cent. The fry are liberated when 5 to 6 

 days old. 



Cost of hatching cod eggs. — As the Flodevig hatchery has been rebuilt and 

 altered several times, it is rather difficult to say how much money has been spent 

 upon it. With the present prices of work and material I should say that a simi- 

 lar station in full working order could be put up for about $5,500. The cost of 

 productions was for the first year about $60 per million of fry, but this price was 

 soon reduced to one-fifth, and at present the fry can be hatched for about $6 

 per million. In this price everything connected with the work is included. 



In 1898 the hatchery produced 412,000,000 of fry from 1,312 liters 

 (590,000,000) of eggs, and imder ordinary circumstances and with an expendi- 

 ture of 12,000 kroner, or $3,150, a similar quantity could be produced every year. 



