874 KEPORT OF COMMISSIONER OF FISH AND FISHERIES. [2] 



the annual meeting of the American Fish-cultural Association April 1, 

 1882. 



I have believed heretofore that every portion of the sac was necessary 

 to the complete development of the fish ; and have been rather amused 

 at the innocent question sometimes asked, " When does the sac drop off! " 

 All fish-culturists have noted the fact that an embryo with a small 

 coagulation in its sac, caused by an injury while in the egg, or after 

 hatching, will die near the time that the injured portion is about to be 

 taken up by the absorbent vessels ; but, to my surprise, I have seen 

 portions of the sac thrown off this winter, and the fish have lived and 

 taken food afterward. 



In this hatchery the troughs were all new, and the haste with which 

 they were made allowed but little time for coating with tar. One trough 

 in particular had but a very light coating, and soon after the hatching 

 of the eggs a singular spotted appearance was observable among the 

 fry. This was caused by the turning white of their livers. Both Pro- 

 fessor Ryder and myself examined them under the microscope, and saw 

 the clouded liver, through which the blood appeared to circulate feebly. 

 Knowing no other cause than the exudations of unseasoned pine wood, 

 I removed the fry at once, and placed them in a well- tarred trough, 

 and watched the result. Neither Professor Ryder nor myself thought 

 that the fish, some 15,000 in number, could live. He was of the opinion 

 that the trouble originated in the sac, and that a deficient circulation 

 in some portion had affected the liver. It was a new experience to both 

 of us, and his extensive knowledge of embryology gave his opinion a 

 weight which led me to accept his view, although I could not see any 

 trouble in the sac at this time. I gave him some specimens afterwards 

 which confirmed this theory, which I am now satisfied was a correct one. 



The first indication of trouble in the sac was an elongation of the 

 posterior portion of it, and a constriction about midway between its 

 extremity and its connection with the body. Sometimes the portion 

 beyond the constriction contained tbe large oil globule, and sometimes 

 it did not; and this globule seemed to be very irregular in its position. 

 All the fish in the trough were so affected, and in addition to the "liver 

 complaint," the blue swelling, oi " dropsy," appeared. The latter was 

 fatal in every case, the microscope showing a deposit of watery fluid 

 between the two membranes of the sac, in which great numbers of blood 

 corpuscles could be seen drifting about. 



In one form, the part cut off from the circulation by the constriction 

 seemed to wither away, and I suspect that only a small portion was 

 affected. In another, a small globe separated from the sac by a cord; 

 and this globe was clear and had no sign of an opaque spot or injury. 

 In a third instance, a larger portion of the sac was cut off by the cord 

 and held suspended, giving somewhat the appearance of the sac and 

 umbilical cord of the skate. Thus far I had but small hopes of the fish 

 surviving, until one day while trying to capture a lively fellow which 



