FISH 



A fish has been defined as, "a back-boned, cold-blooded animal 

 adapted for a life in the water with limbs modified as fins, and obtain- 

 ing oxygen from the water by gills throughout life." The number of 

 difi'erent kinds of fishes present in the waters of the world today has 

 been estimated at roughly 40,000. Since new forms are constantly be- 

 ing described this number is ever changing and always increasing. Fishes 

 easily outnumber all other vertebrates combined, including the am- 

 phibians, reptiles, birds, and mammals. 



A glance at the fishes inhabiting the waters of Maine will convince 

 the observer that they are streamlined ideally for moving through the 

 mediuni in which they live. In general the shape may be described as 

 torpedo or "cigarlike." Some of the fishes have become rounded as 

 the eels and others have become flattened from side to side as the basses 

 and are known as compressed. Fishes of Maine are either rounded or 

 compressed in body form. 



Covering the fish externally is a layer of mucus secreted by the 

 glands of the skin. This mucus protects fish from external infection. 

 Fishermen have long been cautioned to wet their hands before handling 

 fish which they intend to return to the water. Handling with dry hands 

 would remove a large amount of this protective covering and leave the 

 fish exposed to fungus and bacterial invasions. Immediately under the 

 mucus lies the epidermis and under the epidermis are embedded the 

 scales. The scales are laid down shortly after the fish is hatched and 

 reflect changes which may occur in the life history of the fish. Age of 

 fish can be determined from the number of year marks, and periods of 

 good growth and poor growth can be detected from the spacing of the 

 growth rings on the scale. Ages of fishes in this book refer to the num- 

 ber of completed year marks on the scale and conform to the manner 

 in which we ordinarily report the age of a human. Among fishes of 

 Maine the lamprey eel, hornpout, and freshwater sculpin are without 

 scales. Scales of Maine fishes may be divided into the cycloid type 

 and the ctenoid type. Cycloid scales are usually small, and embedded 

 deeply in the skin. Trout and salmon are examples of fish with cycloid 

 scales. Ctenoid scales have several rows of spines along their posterior 

 or exposed edge. These spines, or ctenii, give the fish a rough or spiny 

 feeling. Bass and white perch are examples of fish having ctenoid scales. 



Fins of fishes are thin folds of skin supported by rays, spines, or 

 both. Fish are frequently classified either as "soft-rayed" fish such as 

 trout, or as "spiny-rayed" fish such as bass. Rays are finely segmented 

 and often branched while spines are unsegmented, unbranched, and 

 usually hard. Counts of rays and spines, since their number is reason- 

 ably constant, are frequently of value in identification of closely allied 

 forms. Paired fins include the pectorals located behind the gill open- 

 ings and the ventral or pelvic fins located on the lower side of the body. 



