22 8 The Colors of Fishes 



stood. It is true also that where the red in fishes ceases violet- 

 black begins. 



In the greater depths, from 500 to 4000 fathoms, the ground 

 color in most fishes becomes deep black or violet-black, sometimes 

 with silvery luster reflected from the scales, but more usually 

 dull and lusterless. This shade may be also protective. In 

 these depths the sun's rays scarcely penetrate, and the fish and 

 the water are of the same apparent shade, for black coloration 

 is here the mere absence of light. 



In general, the markings of various sorts grow less distinct 

 with the increase of depth. Bright-red fishes of the depths are 

 usually uniform red. The violet-black fishes of the oceanic 

 abysses show no markings whatever (luminous glands excepted), 

 and in deep waters there are no nuptial or sexual difterences in 

 color. 



Ground colors other than olive-green, gray, brown, or silvery 

 rarely appear among fresh-water fishes. Marine fishes in the 

 tropics sometimes show as ground color bright blue, grass- 

 green, crimson, orange-yellow, or black; but these showy colors 

 are almost confined to fishes of the coral reefs, where they are 

 often associated with elaborate systems of markings. 



Protective Markings. — The markings of fishes are of almost 

 every conceivable character. They may be roughly grouped 

 as protective coloration, sexual coloration, nuptial coloration, 

 recognition colors, and ornamentation, if we may use the latter 

 term for briUiant hues which serve no obvious purpose to the 

 fish itself. 



Examples of protective markings may be seen everywhere. 

 The flounder which hes on the sand has its upper surface cov- 

 ered with sand-Uke blotches, and these again will vary according 

 to the kind of sand it imitates. It may be true sand or crushed 

 coral or the detritus of lava, in any case perfectly imitated. 



Equally closely will the markings on a fish correspond with 

 rock surroundings. With granite rocks we find an elaborate 

 series of granitic markings, with coral rocks another series of 

 shades, and if red corals be present, red shades of like appear- 

 ance are found on the fish. Still another kind of mark indi- 

 cates rock pools fined with the red calcareous alga; called coral- 

 Ima. Black species are found in lava masses, grass-green ones 



