Fish are frequently classified as to whether the fins are positioned 

 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 described as thoracic. If the ven- 

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

 fins is described as jugular. When the ventral fins are posterior their 

 position is considered abdominal. Unpaired fins include the dorsal, 

 adipose, caudal or tail fin, and the anal fin. Although a fish swims pri- 

 marily by muscular movements of its body it depends on the caudal 

 fin lending power to the movements, on the dorsal and anal fins for 

 stabilizing the movement, and on the pectoral and ventral fins for steer- 

 ing and maneuvering. 



Fish obtain their oxygen from water passing over the gills. Closing 

 the gill covers, opening the mouth, and expanding the cheeks causes 

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

 the gill covers causes water to flow out over the gills. Gills are made 

 up of a 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 and of great im- 

 portance to correct management of the fishery concerned. Although 

 internal fertilization and development are known in fishes all freshwater 

 fishes of Maine fertilize the eggs externally. Development, therefore, 

 takes place outside the body of the female. In some fishes the males 

 take on spawning coloration or "breeding plumage" near and during 

 spawning time. Approach of spawning season is the signal in most fishes 

 for a migration to the spawning area. Distances traveled may be many 

 miles as with Atlantic salmon or only a few feet as with lake trout. 

 Certain fishes, particularly minnows and suckers, develop tubercles on 

 the fins and head during the breeding season. These tubercles are more 

 pronounced on males, and are used in grasping the female and in de- 

 fending the spawning area. Some fishes build nests. Female trout and 

 salmon have the job of preparing the nest, but neither parent assumes 

 any responsibility once the eggs are fertilized and covered. Males of 

 the sunfish family prepare the nest, and remain to guard the eggs and 

 young. Many fishes prepare no nest, but merely broadcast the eggs 

 which lie on the bottom among the rocks or aquatic plants. 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 fertilized by a single male. 



Fishes may be classified in two categories according to their food 

 habits. Those that feed on plankton are called herbivores and those 

 utilizing insects and other fishes are known as carnivores. In many in- 

 stances, the mouth and dentition serve as clues to the food habits of 

 fish. An examination of the large mouth and teeth of the pickerel would 

 leave no doubt as to the carnivorous food habits of this species. Like- 



