484 



TJ. S. BUREAU OP FISHERIES 



Ta^e-tal {top 



In 'the case of the Chase or other type of open-top jar the eggs are 

 installed in the manner described. The tube through which water 

 enters is inserted and the flow regulated at the petcock, to give* the 

 desired motion to the eggs. For the removal of dead eggs and shells 

 a piece of rubber tubing is used as a siphon. A short piece of glass 

 tube is inserted in the end of the rubber 

 tube to be introduced into the jar. 



Shad eggs are semibuoyant. The usual 

 period of incubation is from 6 to 12 days 

 in a water temperature 52 to 65° F. 

 These figures represent yeiy nearly the 

 limits of temperature range for the suc- 

 cessful incubation of shad eggs. In a 

 temperature of 50° the incubation period 

 is prolonged to 12 days, while at 75° it is 

 shortened to 3 days, but in neither case 

 can healthy fry be produced. Wliile 

 water temperature appears to be the 

 goyerning factor in the incubation period, 

 other circumstances, not well understood, 

 may also have an influence. Continuous 

 dark and cloudy weather appears to retard 

 and strong light to accelerate develop- 

 ment. 



When hatched, fry are about 0.37 inch 

 long. They have been measured at in- 

 tervals of from 5 to 15 days, from late in 

 May to the middle of October. Toward 

 the middle of August the rate in growth 

 diminishes. Wlien 9 days old, they are 

 about 0.62 inch long. Fry 0.5 inch long 

 July 20 were 0.75 inch long 8 days later; 

 on August 14, 2 to 2.25 inches; September 

 20, 3 to 4 inches; October 1, 4 to 4J^ 

 inches; November 4, 5 to 7 inches. Some 

 years they grow faster than others, and in 

 some streams more rapidly than in others. 

 From the State fishponds at Raleigli, N. C, 

 33 were removed in November, 1884, 

 which measured 8 to 9 inches. Their 

 usual size in tlie Potomac in the fall is 3 

 to 4 inches. 



Fig. 8.— Chase open-top hutcliing jiu- 



MEASURING THE EGGS AND FRY 



To estimate the number of eggs and young fry was for years rather 

 a difficult matter to accomplish satisfactorily. The standard made 

 use of at the outset was undoubtedly mucui too high. The scale 

 most used at present is a light square, made of wood, the longer leg 

 being 15 inches and the shorter 73^^ inches long (fig. 8). The mate- 

 rial is Yi inch wide and }/i inch thick. The graduations arc on the 

 longer leg and read from the lower end upward The first lino is at 

 a height corresponding to the level attained in the jar by a measured 

 half-pint of water, and the succeeding lines are determined by the 



