PISCES ^^2 



General Consideration of the Fishes 



Locomotion in fishes may be by: Swimming, leaping from the 

 water, crawHng or hopping about with the pectoral fins (Angler 

 fish and E. Indian Goby); planing on extended pectoral fins (flying 

 fishes); or wriggling after rains from one stream or pond to another 

 (eel). 



Coloration. — The coloration of fishes is due to the presence In the 

 dermic portion of the skin of (a) special pigment containing cells 

 (chromatophores), (-^) a peculiar reflecting tissue composed of 

 iridocytes. Coloration varies with the species of fishes and may 

 vary in the same fish according to background, age, ill-health, and 

 emotions. 



Sound Producing Organs. — (a) Stridulation. — The bull head uses 

 its preoperculum for stridulation while the gurnard uses its hyoman- 

 dibular bone. In the drumming fish, the postclavicles stridulate 

 with a grooved area on each cleithrum and the air bladder takes up 

 the vibrations. Friction of the upper and lower teeth causes a 

 grinding noise in the mackerel. The sunfish makes sounds like 

 those of pigs grinding their teeth. 



{b) Expulsion of the air from the swim bladder and mouth 

 produces quite noticeable sounds in the eel, the carp and the loach. 

 The eel is said to produce a single note, more musical than any 

 uttered by other fishes. The air-bladder and its muscles in the 

 drum-fish {Poganias chromis) constitute the most powerful sound 

 producing apparatus in fishes. 



Respiration. — The rate of breathing varies with the species, the 

 minnow and the stickleback breathing 150 times per minute, while 

 the blue wrass and the rockling have a respiratory rate of fifteen 

 per minute. Skin respiration, vascular caudal fins and larval 

 external gills are important, while some fishes use the air bladder or 

 develop special accessory organs for aquatic or aerial respiration. 

 Many fishes rise to the surface and swallow the air. The air bladder 

 is used for respiration In the ganoids and many teleosts, and in the 

 " lung fishes." 



Skin. — P/acoid sc3.\es are found in the Elasmobranchs, and while 

 they are usually closely set, we find that in the skate they are scat- 

 tered. In sharks one can trace the evolution of placold scales Into 



ieefh. 



Ganoid scales are hard plates forming an armor in such forms as 



