308 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



in the size of the ova. From larger ova finer and rapidly growing try 

 are produced ; consequently, by a judicious selection of breeding fish, 

 races may be improved, while it is only where segregation is efficiently 

 carried out that such selection is possible. 



96.— EFFECT OF SUNLIGHT UPOK SHAD K«GS. 



By W. F. PAGE. 



In May, 1881, atGunston, Va., ou the Fish Commission barges, I ob- 

 served for the first time the peculiar and astonishing effect of direct 

 sunlight falling on shad eggs. Haviug occasion to make an Amsually 

 large deposit of embryo shad in the channel of the river at a time when 

 our buckets and cans were in use, I used a large shallow tin pan in which, 

 to transport the " leavings " of the cones. Previous to taking the row- 

 boat out to the channel, I placed the pan on the outer deck of the barge 

 and went back to some work in the hatchery. Returning in a few min- 

 utes, I was surprised to see the pau alive with fish, and it occurred to 

 me that this might be brought about by the direct sunlight falling 

 upon the eggs. Since that time I have had abundant opportunity to 

 test this phenomenon, and have adduced the following facts : (1) That 

 the time of hatching any particular lot of shad eggs can be shortened 

 from twelve to fifteen hours by judiciously exposing them to direct sun- 

 light in shallow, highly-polished pans ; and (2) that the fish so procured 

 are fully equal in vitality to those allowed their full time in the eggs. 

 During the spring of 1884, I made a practice at Central Station, when a 

 car shipment was wanted by a given time, of placing the youngest eggs 

 where the greatest amount of direct sunlight would fall on the hatch 

 ing jars, at the same time giving the older eggs less light as develop- 

 ment was more advanced. This was done with a view to hastening the 

 younger eggs and retarding the older, so that the fish for the entire 

 shipment might all hatch about the same time. By this means I have, 

 on several occasions, been enabled to hatch out at the same time differ- 

 ent lots of eggs having a variation in their ages of as much as thirty 

 hours. In my reports of the work at Central Station for the seasons of 

 1883 and 1884 it will be observed that there are considerable variations 

 in the time of the incubation of eggs of the same age ; which is to be ex- 

 plained by the difference in the amount of light the hatching jars re- 

 ceived. I have not been able to observe with the thermometers at my 

 command any increase of temperature in the water employed in the 

 work with the pans, and the pans painted black are entirely useless for 

 the purpose. Though many fish-culturists deprecate the effect of direct 

 sunlight on fish eggs as having a weakening effect on the embryo, ex- 

 perience has demonstrated that the fish assisted in this way are as 

 strong and travel as well as those allowed their full time in the egg. 



Washington, D. C, July 1, 1884. 



