Petromyzontidæ:
Petromyzon marinus, Lamprey eel.
Raiidæ:
Raia sp., Skate.
Some of the scientific names in the above list have been modified by recent research, but it is advisable to present the above classification for purpose of reference. The variations from these names will be given in the part of the discussion relating to the food value of fish, in which the classification of Jordan and Evermann is followed.
Edible Portion of Fish.—As in the case of other animals large parts of fish as taken from the water are inedible. In the preparation of fish the head is usually removed, especially if the fish be of any size, and the entrails rejected. If the fish be scaly, the scales are also removed. The latter vary very greatly in different specimens according to species, size, etc. Usually the edible portion of the fish is larger in quantity than the inedible, though this is not by any means universally the case. Taking fish of all kinds together it may be said that from 55 to 60 percent of the total weight is edible. This, of course, excludes the bones as well as the other portions already referred to.
Principal Constituents of the Flesh of Fish.—In the flesh of cattle, swine, and other edible animals already mentioned it is seen that the protein is the principal part of the edible portion. In many kinds of meat, however, the fat is the principal portion, as in bacon. In the flesh of fish the albuminoids occupy a more prominent part than in the flesh of domesticated animals or game. In other words the proportion of fat, which is one of the principal ingredients of the flesh of other animals, is less than in the other kinds of flesh. The protein in the water-free substance often constitutes over 90 percent of the total matter, and rarely falls below 80 percent. The next most important constituent of the dry flesh of fish naturally is the fat. The average content of fat in the dry flesh of fish is under 10,—it rarely goes above 20 and sometimes falls as low as 2 or 3 percent. The mineral content of the dry flesh of fish is quite constant. It rarely falls below 4 or goes above 8 percent; 5 percent may be regarded as a fair average content of mineral matter. The mineral matter consists chiefly of phosphate of potash and lime, together with some common salt. In the analyses made by Atwater, adopted in the following pages, he grouped together the fish analyzed in proportion to the quantity of the edible portion or flesh which they contained. Groupings were also made on account of the dry substance in the flesh and in proportion to the water and fat which they contained. These tables are of value showing in a general way the relative food importance of the different specimens of fish. This classification is given in the following table:
