368 ZOOLOGY 



time or when in search of food. This fact and the knowledge 

 of places and times are matters of much moment to the fisher- 

 men. The food of fishes is very diverse. Some forms are ac- 

 tively carnivorous, preying on animals as large or larger than 

 themselves (sharks); others, and these are the most numerous 

 class, depend upon small animals such as the young of their own 

 or other species of fish, on Crustacea, insects and worms. The 

 microscopic animals and plants occurring in immense numbers 

 in the water are important items in the food of fishes. Some 

 fishes are scavengers, living largely upon the dead materials 

 found in the water. Fishes differ much in their energy, courage, 

 and resistance to attack. Those possessing these qualities in 

 high degree are denominated "game" fish and are prized for the 

 difficulty involved in their capture. The family of the trout 

 and salmon includes several such species. 



The deep sea habit results in most interesting adaptations. 

 The conditions of life are different from anything we know. 

 Light is absent, the temperature invariable and not far above 

 freezing point, the pressure is something enormous. Many of 

 the fishes are luminescent. Sometimes these luminous organs 

 seem arranged to attract the prey. Some forms have very 

 large eyes to use this weak light ; others are blind as are some of 

 the cave fishes. The sense of touch is greatly developed. In 

 form they are very varied and bizarre. 



388. Economic Value. — Prom primitive times fish has been 

 one of the important human foods. Probably a larger percent- 

 age of the well-known species of fishes are regarded as edible 

 than of any other animal group. Their rate of multiplying 

 and their occurrence in schools at available points are quite as 

 important factors as the delicacy of the flesh in determining the 

 food value of a species. The improved devices for capturing 

 fish, the development of methods of preserving them by drying 

 and by canning, and the increased price of other food substances 

 for which fish may be substituted have all conspired to increase 

 the destruction of the more important edible fish both in the 

 fresh and salt waters. In recognition of this, most nations have 

 appointed commissions for the study of problems connected with 



