PROGRESS IN BIOLOGICAL INQUIRIES, 1931 503 



short distance below the hatchery there is adequate space for the 

 construction of a series of trout pools which will be used for experi- 

 mental purposes and also for holdinf^ brood stock. 



The trout work at this station Avill be devoted primarily to rain- 

 bow and brown trout, although brook trout will also be reared in 

 considerable numbers. The Pittsford station, however, will continue 

 to serve as headquarters for work with this species. As soon as 

 sufficient brood fish have been reared it is planned to undertake 

 selective breeding with rainbow and brown trout along the lines 

 which have given such promising results with brook trout. It is also 

 planned to undertake extensive feeding experiments, which will be 

 continued throughout the year. In accordance with this policy ap- 

 proximately 500,000 rainbow, brown, Loch Leven, and brook trout 

 have been hatched at Leetown, and a large percentage of the young 

 fish will be held over the summer. This will insure an adequate 

 supply of material for experimental work. 



FISH DISEASES 



Herring disease. — An investigation of a disease of the herring in 

 the Gulf of Maine was begun early in 1931 and continued through 

 the summer. This investigation was carried on in cooperation with 

 the division of inspection of the Maine State Department of Agricul- 

 ture, and the greater part of the expenses of the investigation was 

 defrayed by the State. 



During the winter and spring of 1931 a laboratory was maintained 

 at Eastport, Me., where investigations were carried on by Dr. Fred- 

 eric F. Fish and George E. Daniel. Later the laboratory was trans- 

 ferred to the Bureau of Fisheries station at Boothbay Harbor, Me., 

 where much better facilities were available than at Eastport. 



As a result of these investigations it was found that the disease in 

 the herring is caused by a fungus of uncertain affinities known as 

 Ichthyospoi^iwni or Ichthyoplionus. In addition to the herring 

 {Clwpea hai'engus) ^ the parasite has been found on the flounder, ale- 

 wife, and smelt. The herring, however, appears to be the natural 

 host, infection in other species being apparently accidental. 



The parasite occurs in all parts of the body, but is especially 

 abundant in the heart, liver, and lateral-line muscles, and forms 

 large, spherical, multinucleate cells, which are surrounded by a thick 

 membrane. These spherical bodies or cysts occur in groups bound 

 together by a heavy connective-tissue capsule. 



Further development of the cysts takes place by the formation of a 

 small circular opening in the wall, through which the protoplasm ex- 

 tends to form a short, branched hypha covered with a thin trans- 

 parent membrane. The contents of the hypha break up into a 

 number of discrete bodies, the structure of which is practically 

 identical with that of the mother cyst. After the formation of the 

 secondary cysts the tip of the hypha breaks open and the cysts are 

 liberated. Such a process results in the liberation of a large number 

 of bodies into the musculature of the fish, each of which can repeat 

 the process by which it was produced. 

 128210—32 5 



