FISH 



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

 a life in the water with the limbs modified as fins and obtaining oxygen 

 from the water through the gills." The number of difFerent kinds of 

 fishes present in the waters of the world today has been estimated at roughly 

 40,000. Since new forms are constantly being described this number is ever 

 changing and always increasing. Fishes easily outnumber all other vertebrates, 

 the amphibians, reptiles, birds and mammals, put together. 



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

 server that they are streamlined ideally for moving through the medium in 

 which they live. In general the shape may be described as torpedo or "cigar- 

 like." 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 the 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 epi- 

 dermis 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. 

 These changes may be noted in the sculpturing of the scale. Hence the age of 

 fish can be determined from the number of annuli and periods of good growth 

 and poor growth detected. Among the fishes of Maine the lamprey eel, hornpout 

 and freshwater sculpin are without scales. Scales of the fishes of Maine may be 

 divided into the cycloid type and the ctenoid type. Cycloid scales are usually 

 small, round and embedded deeply in the skin. Trout and salmon are examples 

 of fish with cycloid scales. Ctenoid scales are so-called because they 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 hav- 

 ing ctenoid scales. 



The fins of fishes are thin folds of skin supported by rays or spines or 

 both. Frequently fish are classified as "soft-rayed" fish such as the trout or as 

 "spiny-rayed" fish such as the bass. The rays are finely segmented and often 

 branched while spines are unsegmented, unbranched and usually hard. Counts 

 of rays and spines, since their number is constant, are frequently of value in the 

 identification of closely allied forms. The fins are divided into paired and un- 

 paired. Paired fins include the pectorals located behind the gill openings or 



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