254 PEOPAGATION OF FISH. 



hung over the ponds, and as they fall off and drop into 

 the water are readily devoured, and mak&£xcellent food. 

 Or a piece of spoilt meat may be placed in a deep bottle 

 like a preserving bottle, and the flies that will collect in 

 immense numbers during summer may be caught and 

 emptied into the water. This trap will take many times 

 its bulk of flies being kept set all the time and emptied 

 when any one is passing it. Flies are probably the best 

 food that can be given to trout. 



Shad eggs differ essentially from trout eggs and re- 

 quire wholly different manipulation. They are much 

 smaller and lighter. If a trout or salmon egg is dropped 

 into water it sinks at once to the bottom, but a shad egg 

 will almost float, and has but little more specific gravity 

 that the water itself. Shad eggs are less than half the 

 size of trout eggs, and require as their best condition for 

 hatching a temperature of from sixty-five to seventy-five 

 degrees. They will hatch at a lower temperature, but in 

 such cases mature slowly, while eighty degrees of heat is 

 as much as they can endure. When experiments were 

 first made in their artificial propagation, they were placed 

 in ordinary trout troughs, and much trouble was found 

 in their management. If a current of water was turned 

 on to the same extent as with trout, they all washed over 

 the end of the troughs, while if the supply was diminish- 

 ed so that they retained their places, they died of suffo- 

 cation. It was only after many different devices had 

 been tried that the proper invention was discovered — a 

 simple box with the bottom knocked out and replaced by 

 a wire gauze netting. This box is suspended by floats of 

 wood nailed on the sides, so that the bottom is presented 

 at an angle to the current, the degree of inclination being 



