CHAPTER X
THE FOOD VALUE OF FISH
With few exceptions, the different species of fishes that are caught industrially are important because of their food value.
Some fishes are unsuitable for food because they have an unattractive taste; others are directly poisonous. Thus, in the Japanese fish of the genus tetrodon, the roe is poisonous, although the remainder of the fish is edible. Some fishes are poisonous during the spawning season. Others are provided with a special poison gland connected with special spines or barbs. In edible fishes, given the suitable conditions, poisons may be formed by bacterial activity in the flesh of the fish. Poisons so formed give rise to the kind of fish poisoning known as botulism. Cases of botulism have resulted from eating canned salmon and sardines that have become spoiled. In some cases, bacteria present in a diseased fish may produce poisonous substances in the body of the fish. Bacillus paratyphosus has been isolated from some poisonous fish, and certain poison-producing bacteria have been found in others.[2]
Certain shellfish are notoriously liable to be poisonous. The exact nature of the microbes concerned in the production of poisonous substances in shellfish is at present unknown; it is clear, however, that such poisonous substances may be produced in shellfish in three ways—
(1) Microbes of various infectious diseases, such as typhoid fever, may be absorbed by the shellfish from sewage.
(2) The shellfish may be diseased, or be seriously contaminated, by living in dirty water.
(3) Decomposition may set in after the shellfish have been removed from the water—particularly if they have been kept too long in a warm place.