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

 Fish are frequently classified on the location of the ventral fins depending on 

 whether these fins are placed posteriorly or anteriorly on the ventral side or 

 belly of the fish. Most "advanced" fishes have the ventral fins placed under, 

 or nearly under the pectoral fins when the location is spoken of as thoracic. If 

 the ventral fins are in front of the pectoral fins then the location of the ventral 

 fins is known as jugular. Unpaired fins include the dorsal, adipose, caudal or 

 tail fin and the anal fin. Although a fish swims primarily by the muscular move- 

 ments of its body it depends on the caudal fin lending power to the movements, 

 on the dorsal and anal for stabilizing the movement and on the pectorals and 

 ventrals for steering and maneuvering. 



Fish obtain their oxygen from the water by means of the gills. Closing 

 the gill covers and opening the mouth together with an expansion of the cheeks 

 causes water to flow in. Closing the mouth, contracting the cheeks and opening 

 the gill covers causes the water to flow out over the gills. In this manner the fish 

 maintains a steady flow of water over the gills. The gills are made up of a very 

 fine network of capillaries or very small blood vessels with walls so thin that 

 oxygen can pass from the water into the blood and carbon dioxide can pass from 

 the blood into the water. 



The manner of reproduction in fish is interesting to the fisherman and of 

 great importance to the correct management of the fishery concerned. Although 

 internal fertilization and development is known in fishes all the fresh-water 

 fishes of Maine fertilize the eggs externally. Development therefore takes 

 place outside the body of the female. In some fishes the males take on spawn- 

 ing coloration or "breeding plumage" near and during the spawning time. The 

 approach of the spawning season is the signal in most fishes for a migration to 

 the spawning area. Distances traveled may be many miles as with the Atlantic 

 Salmon or only a few feet as with the lake trout. Certain of the fishes particu- 

 larly minnows and suckers develop tubercles on the fins and heads during the 

 breeding season. More pronounced on the males these tubercles are supposedly 

 used in grasping the female and in protecting the spawning area. Some of the 

 fishes build nests. In the trout and salmon the female has the job of preparing 

 the nest while in the sunfish family the male prepares the nesting area. While 

 the bass and sunfish remain to guard the eggs and young the trout and salmon 

 assume no responsibilities once the eggs are fertilized and covered. Many fishes 

 prepare no nest but merely broadcast the eggs where they fall to the bottom to 

 lodge on the surface or in crevices among the rocks. The pickerel and smelt 

 are examples of the latter type. Most fish are polygamous with several males 

 fertilizing the eggs of the female or with the eggs of several females ferti- 

 lized by a single male. 



Although no hard and fast rules can be drawn concerning the food habits 

 of fishes they may be divided into two general groups j one of which feeds on 

 plankton or the herbivorous feeders and the other group the carnivorous feeders. 



