230 Fish Behavior and Angling 



2. Aggregating. Fishes attracted to their kind by favorable temperature, 

 local abundance of food or other environmental detail, but which show 

 no particular polarity as a group, nor is the group capable of any specific 

 diiectional movement. These fish are oriented without reference to other 

 individuals. 



3. Schooling. Fishes sufficiently attracted to one another to impel them to 

 swim in substantially similar paths and perform as a troupe of like-acting 

 individuals in which independence of action is reduced to near the 

 vanishing point. Such a group of fishes is polarized and capable of 

 forward movement as a unit. 



4. Podding. Fishes packed so closely in groups as to leave no swimming 

 clearance, i.e., these fish are actually in contact with one another. The 

 individuals may or may not be polarized. 



Among warm-water species, solitary and aggregating fishes are more 

 common than schooling or podding fishes. Most species of Centrarchids 

 (sunfishes) are solitary or aggregating, although crappies might be con- 

 sidered as schooling under certain conditions. White bass and many kinds 

 of minnows show well-defined schooling, as do bullheads, although under 

 certain conditions the latter form pods. Aggregations, schools, and pods 

 are, in general, without leadership and may shift first in one direction 

 and then in another. Leadership may be evident in schooling fish repre- 

 senting a female followed by a number of males. Schooling may have 

 survival value in that the "confusion efiFect" of a large school of fishes may 

 reduce the precision of a predator's attack. 



Seasonal Rhythm. Most warm-water fishes have a fairly constant sea- 

 sonal rhythm of activities. Being adapted to warm water their movements 

 tend to be inhibited by low water temperatures. Some forms such as the 

 smallmouth bass spend the winter in a quiescent state in schools or 

 groups. Others, such as the northern pike, are quite active in winter and 

 move about constantly. Greenbank ^^ set trap nets facing in both direc- 

 tions across the opening into Target Lake, a backwater area of the 

 Mississippi River (Wisconsin) during 40 days of winter and caught 3328 

 fish, most of which were black crappies, yellow bullheads, and bowfin. 

 He found a positive correlation between total fish movement and the 

 amount of snow cover on the ice. This movement was more related to 

 reduced light conditions than to current, temperature, or dissolved oxygen. 



Breder ^- in his treatise on the reproductive habits of North American 

 sunfishes ( Centrarchidae ) stated that "hibernation" in most species was 

 broken up at about 10°C (50°F) with a general movement from deep 

 water to inshore areas. But not all of the Centrarchids are quiescent in 

 winter. Hansen ^^ found that the crappies in Lake Decatur in central 

 Illinois were more readily trapped in nets in fall, winter, and spring than 



