Distribution of Fish by Species From January 1, 1924

210,000 Brook Trout, fry were received from the Caledonia Hatchery. These fish were produced at the Adirondack Hatchery

DISEASES OF FISH

The work of the year has carried forward the studies of hatchery diseases and those of our public waters. Two diseases afflicting the skin of fry and fingerlings have been diagnosed and the source of origin indicated. Remedies therefor are known. These have been tested successfully and measures suggested for the further prevention of the maladies. Four diseases caused by parasitism of one or more of the internal organs have been diagnosed wholly or in part. Certain phases of the life history of the causal organisms remain to be elucidated before adequate measures of prevention may be considered and adopted.

The Commission has been represented by the Investigator in Fish Culture at two important meetings during the year, before each of which a paper was presented on the subject of fish diseases.

The American Association for the Advancement of Science, Cincinnati, Ohio, December 28, 1923. The life history of Octomitus salmonis, an intestinal flagellate of trout.)

The American Fisheries Society, Quebec, Canada, September 10, 1924. (The transmission of Octomitus salmonis in the egg.)

Introduction.- During the sixty odd years of fish culture a standardized technique has been developed for rearing and handling vast numbers of fish. Progress, however, in the development of physical equipment has quite outrun advancement of knowledge of the physical well-being of the output. The herding of fish in large numbers under the artificial conditions of a hatchery is attended often with serious setbacks. Infectious diseases of one sort or another occur which require prompt treatment to forestall an epidemic and consequent heavy losses.

To make this annual crop of young fish a less precarious one, the Conservation Commission places scientific research in fish diseases in the same category as insurance. That is, insurance against loss of countless numbers of the young by the various ills that fish are heir to.

Some of these diseases are goitre, contagious skin diseases, respiratory troubles, digestive disturbances, deficiency diseases, and on. They represent a formidable array of ills in many respects not unlike human ailments, yet, so far as we know, the germ of only one fish disease, a tapeworm (Diphyllobothrium latum), has been found to be transmissible to human beings. This, it should be stated, presumably has followed the consumption of uncooked fish.

While it is certain that a better understanding of such fish diseases would render the conquest of similar human ills more rapid, it is not from this viewpoint that intensive study has been organized and directed by the Conservation Commission. It is rather to promote the health of the fishes, and thus offset the annual losses that follow in the train of artificial propagation. Already a considerable number of serious epidemic diseases have been diagnosed and remedies prescribed or preventive measures adopted, but many are

still baffling and require continued study of their natural history in order to discover the weak links in the chain of causation.

The business of keeping fish healthy rests obviously far more securely on prevention than on correct diagnosis and treatment. Many troubles in a hatchery arise without doubt out of the conditions of the environment. This is indicated by the fact that the diseases disappear altogether or become greatly attenuated when

the fish are planted into natural waters. For this reason intensive studies in pathology should be augmented by experimental investigations along several lines which would promote the well-being of the fish and at the same time increase the efficiency of the hatchery. Such studies involve the careful investigation of over-crowding, the requirements of food and of oxygen, the freedom from carbon. dioxide, and the adoption of adequate sanitary measures.

Intensive studies of our hatchery diseases and those common to the waters of our public domain are appearing annually in the reports of the Commission. It is contemplated that these shall be brought together eventually in some practical form as a guide or handbook of use directly to our hatchery personnel and to others interested in this larger conservation program of the fishes.