CLASS OSTEICHTHYF.S. BONY FISHES 



389 



Figure 262. Protective resemblance in the flounder. The flounder changes in pattern and 

 color to blend with its surroundings by dispersion or concentration of pigment bodies. Even 

 when placed on such an unnatural background as that on the right, the resemblance is striking. 

 (Courtesy of A.M. Winchester.) 



ently colored chromatophores. The changes 

 are therefore dependent upon the color of 

 the fish's environment and are often pro- 

 tective because they help to conceal the ani- 

 mal. The change in color is slow in some 

 fishes, but usually it only takes a few min- 

 utes, as in the case of the flounders (Fig. 

 262), which respond to pattern of back- 

 ground as well as simple illumination. In this 

 respect flatfishes probably exceed even the 

 famed chameleon. Male fishes are often 

 more brightly colored than the females, es- 

 pecially during spawning activities. 



Sound production in fishes 



A surprisingly large number of fishes can 

 produce sounds audible to man; these noises 

 are used either to bring the sexes together 

 or to warn or startle enemies. Fishes make 

 various sounds in various ways. 



Certain sculpins vibrate their gill covers 

 against the sides of their heads to produce a 

 humming note. The hogfish grunts by 

 gnashing its pharjngeal teeth. The sea robin 

 produces a grunt by means of special mus- 

 cles in the air bladder. In open water, the 

 croaker probably makes more noise than any 

 other kind of fish, it can be heard 30 feet 

 down. The sounds are produced by the ac- 

 tion of special muscles on the air bladder. 

 Croakers are edible fish found along our 

 southern Atlantic Coast. 



Naval men during World War II had 

 more than an academic interest in undersea 

 sounds; at first, some of the noises made by 



fishes and other sea animals threw subma- 

 rine detection by radar into confusion. 



Fishes of ancient lineage 



Among the ancient fishes were those 

 known as the lobefins, because of the thick, 

 lobe-shaped, paired fins. The lobefins con- 

 tain skeletal structures that correspond with 

 similar bony structures in the appendages of 

 true land forms. Descendants of the ancient 

 stocks from which these fishes were derived 

 migrated onto land at a later time to give 

 rise to land vertebrates. Lobefinned fishes 

 were long considered extinct until one was 

 caught off the coast of Africa in 1938. This 

 was a coelacanth {Latimeria) , and about a 

 dozen more have been collected since then 

 (Fig. 263). The chances look good for more 

 coelacanths to be hooked in the future, so 

 that eventuallv we will have a more detailed 

 knowledge of them. As a matter of fact, their 

 internal structure is being carefully studied 

 by Professor Millot of Paris, and we should 

 soon know more about the anatomy of these 

 most interesting creatures. 



The coelacanth is the only surviving mem- 

 ber of the ancient crossopterygian fishes 

 which gave rise to the amphibians. Here we 

 have a valuable link with the past that gives 

 us an understanding of an important group 

 of vertebrates, previously known only from 

 fossils. 



Many of the ancient fishes were covered 

 with ganoid scales. The sturgeons (Fig. 252) 

 and garpikes are protected in this way. Only 



