FISH-CULTURAL PRACTICES IN THE BUREAU OF FISHERIES. 



711 



The hatchery equipment for lake trout at Northville is the common form 

 of wire tray, stacked in troughs of the Clark and Clark- Williamson types." 

 The collections in this region have increased so greatly in recent years, however, 

 that they have outgrown the capacity of the hatchery, and it has been necessary 

 to deepen some of the Clark-Williamson troughs to accommodate more trays 

 during the eying period of the eggs. The deeper troughs are 15 feet long and 

 T,}4 feet wide, with a division through the center the entire length; the width 

 therefore is that of a pair of troughs having a common bottom. The outside 

 depth is 18 inches. Each of the deep troughs contains, besides the bulkhead, 

 15 compartments 19 inches by 10 inches by 16K inches deep, with a capacity 

 of 16 trays i83< inches long by 9K inches wide, on each of which may be 

 placed, if crowded, 10,000 eggs. The total maximum capacity of each pair of 



Lonyifud/na/ Sechon 



Fig. I.— Clark -Williamson trough. 



troughs is then 4,800,000. For best results, 8,000 eggs to the tray, or a total of 

 3,840,000 to each pair of troughs, is a proper number. 



During incubation the eggs seem to do equally well in either up or down 

 current of the Clark- Williamson troughs ; at other stations where eggs are incu- 

 bated in stacks of trays the Williamson type of trough is used. 



As lake trout eggs are taken from fish that have been caught in nets hauled 

 into fishing tugs by steam power, often during rough weather and frequently 

 after the nets have been inaccessible for several days, the percentage of good 

 eggs is not equal to that secured from most of the species manipulated. Con- 

 sequently a large force of young women, who are more deft with their fingers 

 than are men, are temporarily employed to pick over the eggs. A shallow trough 

 with water flowing through it is provided for this work; in this trough, standing 



o For full description of these troughs see Manual of Fish Culture, p. 97-99. 



