428 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. 



quired about six days to emerge from the egg, while iu a temperature 

 between 75^ and 80^ only about seventy hours or three days from the 

 time the eggs were impregnated, the fish were numerous iu the boxes. 



This fact was, of course, a great advantage over the trout, both in the 

 very much less amount of labor in the care of the ova and in the fact 

 that, being in the always precarious egg-stage for such an inconsider- 

 able length of time, they suffered a proportionately less amount of ex- 

 posure to the ills and damages the longer-developing Salmonidcc were 

 subject to. 



The eggs of the shad are somewhat smaller than those of the white- 

 fish, {Coregonus albus, Les.,) which are smaller than in the trout, {Salmo 

 fontinaUs,) and much smaller than in the salmon, {S. salar.) The eggs, 

 just after impregnation, of the white-fish are a little less than one-eighth 

 of an inch iu diameter, while those of the shad are but about one-tenth. 

 The shell membrane is also thinner and the egg more delicate, and 

 does not seem to endure the handling and ladling out into moss or cups 

 for transportation, or even into the hatching-boxes. Experiments in the 

 transportation of shad-eggs, even for short distances, have proved fail- 

 ures, while the white-fish eggs have been sent from Michigan to Cali- 

 fornia, being on the road ten days, and have arrived in good condition, 

 and trout-eggs and salmon-eggs have been shipped much farther, the 

 latter from England to Australia and Tasmania. 



A small percentage of loss occurs in the boxes of shads' eggs, and by 

 careful fish-culturists the dead eggs, detected at once by their white 

 hue, are removed ; but by many are not interfered with, as they are 

 usually too few to occasion very serious damage to the good ones. 



The tool used for their removal is not the egg-tongs or forceps used in 

 trout-culture, but a small net, of minute mesh, less than one-half inch 

 extension measurement, mounted taut on a square frame of wire, about 

 3 inches square, and the bad eggs are floated up to the surface and 

 thrown out with the scaf-net, the good ones passing through the meshes 

 more readily than the bad ones, covered with the mossy parasitic growth 

 that so soon develops upon dead eggs. 



Unlike the fishes of the salmon family, the shad, instead of dropping 

 the ripe eggs into the open cavity of the abdomen to pass backward 

 and out through an ovipore, has a continuation of the oviduct to the 

 outside, the two ovaries in their posterior prolongations uniting into an 

 oviduct, in which, by dissection, the eggs can be seen to pass within the 

 transparent membrane of its walls to its outlet. 



6. — KELATION OF THE TEMPERATURE OF THE WATER TO THE PROPA- 

 GATION OF THE SHAD. 



Temperature of the water of the sea, rivers, and lakes has a very im- 

 portant relation to the increase of the food-fishes, influencing the time 

 of the spawning migration, the development of the eggs, and the wel- 



