BULLETIN OF THE UNTIED STATES FISH COMMISSION. 445 



ol" oyster culture, and, by the educatiou of the community, to biisten the 

 time when wiser laws will reuder our natural advantages available for 

 the beuetit of our people. 



The most economical method of constructing floats must, of course, 

 be determined by practical experiments, but a float constructed by con- 

 necting two old ship- masts together by string-pieces, with a bottom of 

 coarse galvanized iron netting, would have sufficient buoyancy and 

 enough resistance to water to support a large quantity of submerged 

 shells and oysters for two or more seasons, and a coating of copper paint 

 each year would protect the timbers from worms. 



The floats sliould be open at the ends, to i)ermit free circulation, and 

 they should be moored in such a way as to swing with the current. 



131.— SOITIE OF TIIli: I.IFE-IVEEDS OF FISH.* 



By Dr. OTTO ZACHARIAS. 



Water is the main condition of the life and well-being of fish. The 

 water should contain food in the shape of infusoria, snails, worms, and 

 insect larvaj, but people trust to kind nature to furnish a constant sup- 

 ply of these. In the vast majority of cases this confidence is somewhat 

 well placed, but as a general rule nature will supply only the absolute 

 needs. If a good harvest of fish is to be a certainty, the needs and 

 habits of fish should be thoroughly studied, and care should be taken 

 to remove everything which will interfere with these needs and habits. 



Fish breathe through their gills, which consist of four double rows of 

 cartilaginous leaflets. The blood-vessels distributed through them give 

 to the gills a bright red color. Four bony arches support the double 

 lamellte, which exercise their important functions under a piece of horny 

 skin called the " gill-cover." For the purpose of breathing the fish 

 passes water into the branchial chamber ; here it comes in contact with 

 fringe-like leaflets, which it supplies with oxygen. The water makes 

 its escape by the gill-opening. If you take a fish out of the water its 

 breathing process is interrupted, the gill-leaflets begin to shrink, and 

 become dry, when they are unable to absorb the needed air from the 

 atmosphere. 



Any one who has carefully examined the gill-fringes of a whiting or 

 pike must be convinced that these tender organs will be injured by 

 muddy or impure water, just as our lungs are injured by inhaling bad 

 air or air filled with particles of dust. The first point to be observed, 

 therefore, should be to prevent water, in which fish are to be kept, from 

 becoming impure by the refuse from factories, mines, &c. Eefuse float- 

 ing in the water will exercise some chemical, but principally a mechan- 

 ical, influence by constantly irritating the respiratory organs. In this 



* " Uthe7- di" Lchensbedurfinsse der Fibche." From Mit1heiluni)en des Westjjreussischcn 

 Fisclierei-Vereina, No. 5, Dautzic, MarcJi 4, 1886. Translated by H. jACoesoif, 



