6 FISHES AND FISHERY METHODS 



median line of the back are termed dorsals, and depending on the species, 

 there may be one, two, or three such fins. Along the median ventral line 

 there may be one or two fins which are termed anals. The tail of the fish 

 is referred to as the caudal fin. Various fins are, at times, absent, depend- 

 ing on the species, or may be (in the case of the dorsal and anal fins) con- 

 tinuous along the back or mid-ventral line. In some fishes such as smelts, 

 trout, and salmon the second dorsal is characterized by a complete 

 lack of supporting rays, the fin being a fleshy protuberance. A fin of this 

 type is referred to as an adipose. 



Fins of fishes are characterized by the nature of the supporting rays. 

 Those fishes whose fins lack spiny supporting rays, such as salmon and 

 trout, are called soft-rayed fishes, while those having fins supported 

 partly or totally by spinous rays are referred to as spiny-rayed fishes. 



The greatest number of median fins generally occurs in the cod family 

 which has three dorsals and two anals (Figure 1.2c). The clupeoids 

 (herring, sardine, menhaden, etc.) possess only one dorsal fin. 



There are a number of adaptations of fins for specialized uses. In the 

 remoras the first dorsal has been modified into a sucker-like disc which 

 the fish utilizes in attaching itself to other marine animals. By contrast, 

 lump suckers have a modification of the pelvic fins which form an adhesive 

 disc. In the trigger fishes (Bahstidae) the first dorsal has a strong, stout 

 spine which may be locked into an open position when assuming a defen- 

 sive posture. In some of the more rapid swimming fishes (tuna and marlin) 

 grooves occur along the median and ventral line into which the dorsal 

 and anal fins may be recessed during swimming. The elongation and 

 enlargement of the pelvic and pectoral fins in flying fishes is an excellent 

 example of specialized use of the paired fins. Although these fins are not 

 used for actual flying in the sense of propulsion, they are employed for 

 gliding or soaring. 



A fish generates most of its propulsive power through undulations of 

 the body and rapid lateral motion of the caudal fin in the water. The 

 remaining fins generally serve in balance and turning. However, in some 

 fishes the lateral fins are also utilized for propulsion. 



Protective Covering 



In the majority of modern fishes the body is covered with scales, 

 although a few are naked. Fish scales vary greatly in shape and size 

 and are usually grouped into two categories: cycloid and ctenoid. Cycloid 

 scales are characterized by smooth posterior margins and are frequently 

 found in fish having soft dorsal fins, such as salmon and trout"*. Ctenoid 

 scales have coml)-like (spinous) posterior margins. They are commonly 

 found in fishes having spinous rays in the dorsal fin. Both types of scales 

 occur on some fishes. In the more primitive, bony fishes such as sturgeon, 



