456 TEXTBOOK OF ZOOLOGY 



annually are yielded by the commercial fisheries. The annual catch 

 of salmon alone is estimated at $17,000,000. Besides salmon, cod- 

 fish, halibut, herring, shad, mackerel, mullet, red snapper, buffalo 

 fish, carp, catfish, trout, ciscoes, and pike perch are all important 

 food and commercial fish. In addition to the food value of the 

 flesh, the eggs of several species, such as sturgeons and paddlefish, 

 are in great demand as caviar. Several of the food fish are also 

 greatly prized as game fish. Many of the game fish, such as bass, 

 crappie, trout, and the pikes, are choice food. Some highly desirable 

 game fish, such as the tarpon, are almost worthless as food. 



Several groups of fish have a distinct negative value. The sharks 

 destroy many other fish, lobsters, and crabs; damage perhaps one- 

 half million dollars' worth of fishing gear per year, as well as the 

 larger ones, injuring or even killing a human being occasionally. 

 Certain rays, such as Dasyatis sahina and D. americana, have a 

 poisonous spine on the tail, and the pectoral fins of catfish have a 

 barbed poisonous spine. Either of these fish can inflict an ugly, pain- 

 ful wound which is dreaded by all fishermen. 



The United States government through the U. S. Fish and Wildlife 

 Service and most states through their Fish and Game departments are 

 making continuous studies of the fishing industry and are conduct- 

 ing fish culture on a rather large scale. 



The gar pike is decidedly a predator, living largely on other fish. 

 The value of the sport of fishing is usually underestimated. Besides 

 having recreational value, there is much money spent on the trips, 

 tackle, clothing, etc., inspired by this sport. 



There are still several other valuable relations of fish to the welfare 

 of man. Such oils as cod-liver oil, haliver oil, shark-liver oil, espe- 

 cially, are much used as medicinal products for production of vitamin 

 D which is a preventive for rickets. Fish scrap, which is left after 

 the oil is extracted, is used as a fertilizer and is also put up in the 

 form of fish meal and sold as protein feed for other animals. The 

 hides of sharks and some other fish make fine leather when tanned. 

 Ganibusia, a top minnow of the South, called the mosquito fish, is 

 an asset because of its appetite for mosquito larvae. It is used to 

 control the spread of mosquito-borne diseases, such as malaria, yellow 

 fever, and dengue fever, by destroying mosquitoes. A liquid, known 

 as pearl essence, is extracted from certain fish scales in an ammonia 



