542 "U. S. BUREAU OF FISHEBIES 



dried seaweed contains 900 and batli sponge 3,870 milligrams per 

 kilogram. In fact, man depends on tne concentrated supply of 

 iodine in the seaweed for an important part of his supply of that 

 element. Mussels in fresh water that contains only 0.0000066 per 

 cent manganese may contain as much as 2.1 per cent of the metal 

 in the liver (Bradley, 1910). Copper, as will be seen below, may be 

 present in considerable quantity m oysters, though its quantity in 

 sea water is very slight. Silicon is dissolved in sea water to the extent 

 of only 0.2 to 1.4 parts per million, yet it makes up the shells or 

 skeletons of billions of diatoms, the most important ultimate source 

 of food in the sea for larger organisms. Calcium, occurring in 

 relatively small quantity in sea water, constitutes the greater part 

 of the shells and skeletons of nearly all animals in the ocean. Iron 

 is the principal source of red color in the shells of mollusks and is of 

 vital importance in the blood of all red-blooded animals such as 

 fish. It is also stored in considerable quantity in the hepato-pancreas 

 or liver of oysters and clams, yet it exists in only a small quantity 

 dissolved in sea water. Phosphorus is not in great concentration 

 in sea water, but it is essential to life and is concentrated as calcium 

 phosphate in bones and in organic compounds of fundamental 

 miportance in the life processes of marine animals. 



The organisms thus perform a most important function in collect- 

 ing the needed elements of the ocean in acceptable form for human 

 food. 



ANALYTICAL DATA CONCERNING MINERAL SUBSTANCES IN FISH 



AND SHELLFISH 



It must be admitted that chemists have neglected the inorganic 

 in favor of the organic constituents of fish. The analyses usually 

 made give data concerning fat, protein, etc., but the ash has not 

 often been completely analyzed. This neglect seems the more 

 noteworthy in that one of the most important distmctions of fish in 

 comparison with other foods exists in the inorganic constituents. 



ASH 



Most of the analytical data relating to the mineral matters in 

 fish are for total ash, from which^ in some cases, individual elements 

 have been separated and determmed. Table 21 gives data relating 

 to total ash, phosphorus, and sulphur of some common sea foods 

 that are fairly representative of fish and shellfish in general. 



