CULTURE OF THE SHAD. 157 



eaten in deep water, transmitted a deep-water instinct to 

 his children, who thereby flourished, while the shoal-water 

 fry got in due time exterminated ? 



" So the fry must be let go in the proper way by towing 

 the boxes into mid stream, or by liberating them during 

 the night, when their enemies do not feed. In either case, 

 the trap-slide must be raised, when they will be carried 

 gradually through the coarse netting by the current. 

 This operation must be performed as soon as all the ova are 

 hatched out. There ends the nursery care ; for we know 

 no method of keeping the young till they have gained size 

 and strength. What we may hope to avoid is, the enor- 

 mous loss which the eggs themselves suffer, when deposited 

 by the natural method.* 



" The ovaries of a full-grown shad weigh at the spawn- 

 ing season about thirteen ounces, without the membranes. 

 With a common lens, three sizes of ova are at once distin- 

 guished. The first have a diameter of T ^ to y^ of an 

 inch. These are transparent and ready to be laid; the 

 second, T ^ to T Q of an inch; the third, T | 5 of an inch. 

 These two smaller sizes are opaque ; they are still found 

 after the fish has spawned, and are the crops ready to 

 mature the next year and the year after. This state of the 



* With the utmost care to secure every favorable surrounding, 

 Green was never able to hatch more than two per cent, on the 

 natural river-bed. Only those eggs hatched that chanced to catch 

 in an angle of the gravel, where they had the current all about 

 them. This dpes not take into the account those that are not im- 

 pregnated, or are devoured, or covered by mud, &c., &c. 



14 



