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MARINE PRODUCTS OF COMMERCE 



diameter in small fish. For example, a specimen of catalufa, Priacanthus arenatus, 

 11 inches long, had eyes l/s inches in diameter. Even proportionally larger eyes 

 occur in some of the bizarre deep-sea fishes. Then there are quite a few groups 

 of fishes that have no functional eyes at all, the best known among them the cave- 

 dwelling blindfishes. 



It is generally believed that sight in fishes, even those with large eyes, is poorly 

 developed. As the lens is round most species are probably quite near-sighted. 

 The author learned from experiments that the mosquito fish, Gambusia affinis, 

 cannot see a wiggletail, or mosquito larvae, one of its principal foods, at a dis- 

 tance greater than approximately 3 inches and that it apparently cannot dis- 

 tinguish a bit of leaf stem or twig from a wiggletail at any distance within its 



{Courtesy U. S. Fish and WildUfc Service) 



Fig. 10-20. Naked star-gazer (Astrocopus anoplus). Family: Urmwscopidae 



( Stargazers ) . 



range of vision. Furthermore, it seems to be able to detect motion more readily 

 than the object itself. Thus, a wiggletail may escape notice when within the range 

 of vision of the fish if it remains motionless. Moreover, it was learned that 

 Gambusia does not feed in darkness and will do so during the night only when 

 light is provided. 



It is evident, then, that some fishes depend largely upon their eyesight to find 

 food, whereas others, though blind, manage to live. Then, it is perhaps correct to 

 say that eyesight is developed in fishes just to the extent needed in the environ- 

 ment in which they hve and for the particular kind of food they require. 



The Ear. Although fish have no external ear, they have an internal one, con- 

 sisting chiefly of semicircular canals in which ear stones, or "otoliths," are found; 

 these lie very close to the brain. It is certain that at least most fish can "hear," 

 even though hearing may consist chiefly in detecting disturbances in the water. 

 Hearing may be aided in some species by delicate sense organs within the lateral 

 line, to which further reference will be made in a subsequent section. 



The Nostrils. The vast majority of fishes have 2 pairs of pits variously situated 

 in the snout, though usually lateral and in front of the eyes. Some species, how- 

 ever, have only a single nasal opening on each side of the snout. The nostrils in 

 fishes, unlike those of the higher vertebrates, do not communicate with the throat. 

 Through experimentation it has been proved that at least some fish can detect 



