CHARACTERISTICS OF MARINE FISHES 169 



Even then they may not have the color pattern of adults. In general young fish 

 tend to have the color pattern of females and do not become differentiated in this 

 respect until about the time of sexual maturity. Even then the old males are 

 usually more brilliantly colored than the young ones. Striking examples of con- 

 fusion in classifying the brilliantly colored labroid and parrot fish have occurred 

 because of pronounced differences in the color among individuals, between the 

 sexes of one species, and between the young and adults. Males have been 

 described as specifically distinct from their females and young distinct from 

 their parents; even individuals of one species vary so prominently in color that 

 they have been considered distinct species. 



Nuptial or breeding colors are common among fresh-water fishes, but rather 

 rare among marine forms. In general males respond to a greater extent in this 

 respect than females. Commonly, the fins of fresh-water fish become yellowish 

 or red when the animals are in spawning condition. Frequently, these bright 

 colors spread over at least the ventral section of the body in the males. 



It is not yet possible to explain the utility, if indeed there is any, of the colors 

 and patterns of fishes, as already indicated in regard to the brightly colored 

 tropical-reef fishes. As pointed out above color in some fishes provides pro- 

 tection, and it has been thought that sexes at breeding time recognize each other 

 by certain special markings. However, to the taxonomist the red, blue, green, 

 yellow, and black spots, bars, ocelli, and other color markings serve as recognition 

 marks in determining species. 



Foods 



The type of food consumed by any species of fish is dependent on the structure 

 of its mouth, teeth, gill rakers, and digestive tract. As these organs difi^er widely 

 in structure, it follows that the foods upon which fish feed also vary widely. There 

 are indeed few aquatic animals of suitable size upon which fish do not feed, and 

 some terrestrial ones, such as insects and birds, are included. 



Some species are quite restricted as to food; others are virtually omnivorous. 

 The black drum, Pogonias crotnis, to which reference was made in the section 

 dealing with teeth, feeds on the bottom and subsists almost entirely upon moUusks 

 and some crustaceans, which it is able to crush with its broad, flat pharyngeal 

 teeth. Spadefish (Chaetodipterus) , on the other hand, feed mainly on small 

 plants, especially algae, which they are able to rasp from submerged objects with 

 their cardiform teeth. Codfish, Gadus morhtia, are omnivorous, and fish of many 

 different species, including their own, have been found in their stomachs. They 

 also feed on shrimp and other crustaceans, both the surface and bottom-dwelling 

 forms. Even a wild duck is occasionally captured. Also found in their stomachs 

 are stones, probably taken incidentally with the hydroids, sea anemones, or other 

 growth attached to them. However, such indigestible objects as pieces of wood 

 and rope, fragments of clothing and old boots, a tobacco tin, and jewelry have 

 also been removed. It is highly probable that cod, like many other fish, snap up 

 and swallow any moving animals or objects in the water. The failure to dis- 

 tinguish between live edible animals and indigestible objects is due to their in- 

 ability to see them clearly even at a distance of perhaps 2 or 3 inches, or less. 



The size a fish attains offers no reliable criterion as to the size and kind of food 

 it eats. Thus, the whale shark, the largest living fish, feeds on minute organisms, 



