140 FISH CULTURE 



troughs they must be held in place by some 

 means. To do this several methods are em- 

 ployed. One quite common is a V-shaped 

 wedge of wood, inserted between the troughs 

 and one side of the tray. Another is to make 

 the trays of material so light that the weight 

 of the eggs will keep them submerged; when 

 this latter method is used it is necessary to 

 fasten at the under corners screw-eyes, or 

 blocks of wood, to keep the trays from settling 

 entirely on the bottom, and thus run the risk 

 of being covered with sediment and injured. 

 Trays are sometimes weighted enough to keep 

 them down, or are slipped beneath cleats on 

 each side of the trough so as to slide in and 

 out after the manner of drawers in a desk. 

 This is perhaps the best way. 



Care of the Eggs. There is always a quantity 

 of unfertilised eggs in every lot taken. Some 

 of them are frequently detected as soon as the 

 washing is finished. They are marble white, 

 opaque, and sometimes show the micropyle in 

 the form of a yellowish spot. Within 48 hours 

 after the eggs have been placed upon the trays 

 others which were not fertilised begin to show 



