BREDER: FISH SCHOOLS AS OPERATIONAL STRUCTURES 



Table 1. -Location of individual fishes (Trachurus) by quadrants and by halves. 

 Data based on figure 2 of Hunter (1966). (First letters, L and R = left and right. 

 Second letters, F and R = front and rear.) 



loose nature- it is remarkable that any such ap- 

 proximation to a regular figure could be found. 

 This material indicates that the influence tending 

 to hold schooling fishes to approximating figures 

 this close to geometrical regularity is effective 

 even in assemblages of fishes barely coming with- 

 in our definition of the word. 



Healey and Prieston (1973) brought out a very 

 interesting feature of schools by the application of 

 multivariate analysis. This is evidently closely 

 related to the preceding geometrical study on the 

 data presented by Hunter (1966). The problem of 

 the origins or the reasons for the existence of these 

 individual variations in fish movements within a 

 school is not yet susceptible to a general solution. 

 Clearly some are caused by extrinsic stimuli and 

 some by intrinsic causes, such as the physiological 

 state of the individual. Healey and Prieston (1973) 

 wrote that their data suggested, ". . . that there 

 may be a short-term and a long-term organization 

 within the school." Possibly this could eventually 

 be referred to equivalently short- or long-endur- 

 ing stimuli, not grossly evident to the observer. 

 The data of McFarland and Moss (1967) and Moss 

 and McFarland (1970) may represent an intrinsic 

 short-term event, in this case being a reduction in 

 oxygen tension. Alekseeva (1963) showed that 

 various fishes have a greater oxygen consumption 

 when visually isolated from their fellows. Such 

 individuals, if able to see the others, do not. 

 Schuett (1934), Escobar et al. (1936), and Breder 

 and Nigrelli (1938) indicated that individuals of 

 Carassius auratus (Linnaeus) swam faster when 



alone and when crowded, but slower when with a 

 few companions. This should be reflected in their 

 oxygen demand and may account for the results of 

 Alekseeva (1963). 



The very short duration of the Hunter (1966) 

 data suggests that the details here might be based 

 on intrinsic sources, as in the case of the fish that 

 kept the leadership of the school and of the one 

 that brought up the rear. It is conceivable that 

 these may be the consequences of the individual 

 physiological states. 



In agreement with Bowen (1931, 1932) and 

 Radakov (1972), there is no convincing evidence 

 that the superficial appearance of "leadership," to 

 be seen occasionally, supports such a view. 

 Hunter's (1966) data covered only 8V3 s. Breder 

 (1959) suggested that "white" Carassius auratus 

 (Linnaeus) seem to take the leadership in schools 

 otherwise composed only of "yellow" individuals. 

 This finding of white fishes in leading positions is 

 apparently related to the greater conspicuousness 

 of the white fish as compared with the yellow in a 

 lily pond environment and is not an indication of 

 leadership by any individual. 



Radakov's (1972) data, which was extensive and 

 important, considered "leadership" in a rather 

 different sense than the others. He considered 

 numbers of leaders up to 40% of the number of 

 fishes comprising a school. The front fishes, with 

 no other fishes ahead of them, are considered here 

 as leaders. These fishes are in a different physical 

 category as they have none of the advantages of 

 being a following fish. 



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