XIV REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
tion respecting the times of occurrence, the abundance, life histories, 
habits, diseases, parasites, etc., of the useful fishes and marine inverte- 
brates. The Roosen process of preserving fresh fish, which has at- 
tracted much attention in Europe, was given several trials, with the 
expectation of finding it adapted to the preservation of bait for the 
offshore fishing vessels, a problem of unusual importance at the pres- 
ent time. It proved to be entirely unsuited to this purpose, however, 
the fish placed in it becoming too soft either for bait or for food, though 
generally free from the offensive odors of decomposition. Many large 
aquaria were added to the equipment of the lower floor of the labora- 
tory and fish-hatching building, and under Mr. Seal’s arrangements 
gave excellent opportunities to observe the habits of even large-sized 
fishes, of which an abundant supply for that purpose was always kept 
on hand. During the hatching season it was intended that these aqua- 
ria should be used for the temporary storage of the fry. 
B.—SPECIAL INVESTIGATIONS. 
Temperatures and densities—One of the most important scientific 
problems before the Fish Commission has been the determination of 
the temperature and density of the water along the sea-coasts and in 
all inland lakes and rivers which afford valuable fisheries, or might be 
suited to that purpose. The object in studying these physical charac- 
teristics is at least twofold: First, to ascertain the influence of tem- 
perature and density on the movements of those migratory fishes which 
form so large a proportion of the fishery production of the country, 
and the appearance and abundance of which during any fishing season 
may possibly, in a measure, be predicted by a thorough knowledge of 
the physical conditions essential to their well-being; second, to fur- 
nish a guide in the transplanting of fishes and the stocking of any 
region with the species most likely to survive and propagate. General 
results are not so important or so applicable to this study as special 
series of observations continued from year to year. In the furtherance 
of this object, observations of temperature, and where expedient de- 
terminations of density, were made at all of the stations of the Com- 
mission during the entire year, or while operations were in progress. 
The same observations were made with great care by the vessels of the 
Commission, whether in port or cruising, and generally at intervals of 
one hour. The bottom and serial temperatures, and other physical 
data obtained by the steamer Albatross, on the fishing banks and in 
deep water, are of special value in the same connection. The most 
important continuous series of surface temperatures, however, are those 
taken for the Commission by employés of the Light-House Board. and 
Signal Service along both sea-boards of the United States, at several 
stations on the Great Lakes, and upon some of the most important 
shad and salmon rivers on both sides of the continent. This co-opera- 
tion between the two bureaus just mentioned and the Fish Commission 
