GROWTH, MIGRATIONS, FOOD AND HABITS 



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the length and proximity to one another of the gill-rakers con- 

 stitute a special apparatus for straining minute organisms from 

 the sea-water. The gill-rakers are stiff horny rods projecting 

 forwards from the inner and front edges of the gill-bars, and 

 in fishes which feed on large animals they are short and far 

 apart, so that the gill-apertures are wide and unobstructed. 

 But in the herring, shad, pilchard, &c., the projections are long 

 and close-set like the teeth of a comb, and thus fill up the 

 whole of the gill-apertures with an efficient straining apparatus 

 (Fig. 83). The fish takes gulps of the water containing crowds 

 of copepods, &c., and passes the water through its gill-rakers 



Fig. 83. — The gill-lmrs and gill-rakers of the Herring, the gill-filaments which are 

 attached to the outer sides of the gill-bars having been removed. 



The way in which the sides of the upper jaw are brought to 

 the front of the gape when the mouth is open, is also probably 

 of some advantage in the process of feeding. The mackerel, on 

 the other hand, pursues separately the small fish on which it 

 preys, hunting them by sight ; its activity and speed are its 

 special adaptations in addition to its tweezer-like jaws. The fact 

 that mackerel are so easily caught with artificial bait having a 

 shining surface and moving through the water, and that they 

 will bite at almost anything attached to the hook provided that it 

 is moving, shows clearly how they are accustomed to snap at 

 small fish and are guided by their eyes, not by smell, touch, or 

 taste. Fish that thus trust to their sight naturally feed in the 

 daytime, and fishing for them with hook and line must be carried 



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