BY-PRODUCTS OF FISHERY INDUSTRIES 221 



prepared from most species of sharks resemble cod- 

 liver oil in appearance and composition. Some shark- 

 liver oil finds use medicinally in the Orient, but most 

 of it is utilized in the currying and tanning of leather. 

 Skate-liver oil is manufactured chiefly in India, 

 although some is occasionally prepared in North 

 Carolina. This oil is also used medicinally in the 

 Orient. 



Fish Scrap 



Fish scrap is a by-product of fish-oil manufac- 

 ture. An immense quantity of fish scrap is manufac- 

 tured; more than a hundred thousand tons is pro- 

 duced annually in the United States alone. The two 

 important uses of this product are for meal and as 

 fertilizer. Somewhat more care is used when fish 

 scrap is prepared especially for meal, but most fish 

 scrap is now of a good enough quality to make a 

 satisfactory feed. 



Fish have been used as manure almost since the 

 beginning of agriculture. When the colonists first 

 came to America, they found the Indians putting a 

 fish beneath each hill of corn. The fish rotted and 

 caused the corn to grow much faster. Just why the 

 decaying fish caused an increased growth of corn was 

 not understood by the Indians. An early German 

 chemist, Liebig, often called the Father of Agricul- 

 tural Chemistry, was one of the first to show that 

 decaying fish furnishes plants with two important 

 elements required for growth; namely, nitrogen and 

 phosphorus, elements lacking in most soils. Nitro- 

 genous fertilizers such as fish scrap aid in the growth 

 of all crops on nearly all soils, except those such as 



