7o6 BULLETIN OF THE BUREAU OF FISHERIES. 



21 in a water temperature of 46°. Practically all the fish had finished spawning 

 on April i, at which time the water temperature was 58°. The spawn is taken 

 daily from the crates and transferred to the hatchery in buckets. 



The eggs are comparatively heavy, and are slightly adhesive when first 

 deposited. The period of incubation in a water temperature of 47° to 54° is 

 ten to twenty days. The absorption of the yolk sac requires a period of eight 

 days in a mean temperature of 54°. On the Potomac River the average number 

 of eggs from fish of one-half pound weight is about 15,000. 



When measured into the jars the eggs are computed at 100,000 to the 

 quart. Actual measurements of 10 eggs average 1.662 millimeters or 0.065 

 inch in diameter, but on account of the peculiar gelatinous envelope of the 

 egg, these individual egg measurements are of no use whatever in estimating 

 the number in a given volume. 



STRIPED BASS.. 



At Weldon, N. C, is a field station for the propagation of the striped bass 

 (Roccus lineatus). It has been operated for a number of years with rather 

 negative results as to the number of eggs collected, but with experience of much 

 value as suggesting lines of improvement in methods of manipulating ripe fish 

 and the eggs. 



The chief obstacles to successful work in the propagation of this fish are 

 the difficulties of obtaining ripe spawning females in numbers sufficient to pro- 

 duce large results, and of obtaining a ripe male at the time a female is available. 

 Penning the fish has not proved successful. The delicate nature of the eggs 

 and the limited period of incubation — 1% days — are reasons for believing that 

 they can not be successfully transported from the source of supply. 



The McDonald automatic hatching jars have been somewhat successfully 

 used at Weldon, but the sac fry of the striped bass are more tender than those 

 of any other fish and it was found that many were injured in their passage to 

 the aquarium through the rubber tube of the closed top. The style of jar was 

 then changed to open top, and has given highly satisfactory results. An 

 elongation of the pitcher mouth by means of a trough of canvas delivers the 

 fry from the jar to the aquarium without friction and concussion. Owing to 

 the buoyancy of the eggs less than one quart of water per minute is supplied to 

 each jar and at time of hatching only about one pint. When water hardened 

 the eggs are computed at 35,000 to the liquid quart and it is customary to 

 incubate 80,000 in each McDonald jar. 



In the latitude of Weldon, striped bass spawn in a temperature of 70° to 

 77°, the season being from the middle of April to early in June. 



