BREDER: FISH SCHOOLS AS OPERATIONAL STRUCTURES 



Rosen and Corn ford (1970, 1971) had shown by 

 means of a special type of rheometer that there are 

 great diflferences in the friction reducing abilities 

 of the slime of various species of fishes. See 

 Jakowska (1968) for a discussion on the extent of 

 the wide variety of other kinds of utility ascribed 

 to the mucus of various fishes. It would seem to be 

 certain that these effects are dependent on the 

 polysaccharides inherent in fish mucus, although 

 for present purposes it is not necessary to know 

 just what components of fish mucus account for 

 friction reduction. 



Successive dilutions of fish slime with the water 

 of the individual's habitat have been plotted 

 against reduction of friction in terms of percent 

 by Rosen and Cornford (1970, 1971). In some cases 

 the curve rises extremely rapidly, reaching a 

 reduction of turbulent friction of over 60% with 

 water dilution to only 5% mucus. Others, with 

 evidently less potent slime, show a much smaller 

 rise in friction reduction, reaching 50% or less with 

 a water dilution to 50% or more of slime. The most 

 extreme case reaches only 8% reduction in friction 

 with full strength slime. 



It is notable that the two species with the fastest 

 rise in friction reduction are rapacious and strike 

 at relatively large prey. These fish can move from 

 a resting position to their highest speed in a 

 remarkably short time. The three species at the 

 other end of the friction reduction series feed on 

 much smaller organisms in proportion to their own 

 size, for which violent pursuit is completely un- 

 necessary. The two species with the most efficient 

 drag reduction do not form obligate schools and 

 are often solitary, while the three with the least 

 effective mucus are schoolers and only one drops to 

 the facultative status. 



The preceding data on the reduction of tur- 

 bulent friction by means of long-chain polymers, 

 and the demonstration of the great effectiveness 

 of the mucus exuded by some fishes, as well as the 

 geometrical {)atterns in which schooling fishes 

 arrange themselves, leaves little room for doubt 

 that the fishes so organized may attain a locomotor 

 advantage from the mucus trail trapped in the 

 vortices left by the fishes that preceded them. 



The fishes with sharp rise in friction reduction in 

 Table 8 and P'igure 20 are all nonschoolers or at 

 most facultative: Paraiichthyi^ californicus 

 (Ayers), Sphyraena argentea Girard,''' and 

 Micropterus dolomieui Lacep6de. Those with a 

 slow rise in friction reduction are all schoolers and 

 are primarily obligate'" schoolers: Scomber japon- 

 icus Houttuyn, Sarda chiliensis (Cuvier), with 

 Saimo frutta Linnaeus and S. gairdneri Richard- 

 son as facultatives. The nonschoolers are capable 

 of showing a sudden acceleration from a resting 

 position and apparently attain their highest pos- 

 sible speed in a matter of seconds or less. The 

 hydrodynamic aspects of extreme acceleration 

 from a position of rest, shown by slender fishes 

 such as barracuda, are treated by Weihs (1973b). 

 This can be critical in overtaking relatively large 

 prey. Schooling fishes that normally swim at a 

 continued steady pace evidently cannot perform in 

 such a manner and even the marginal members 

 seldom try. 



Uskova and Chaikovskaya (1975) noted, in a 

 paper on the chemical nature of the protein com- 



'•''It is recognized that the Pacific Sphyraena argentea tends to 

 form schools more readily than the larjjer Atlantic .S. barracuda 

 which is usually solitary. The smaller Atlantic conf?cners ap- 

 proach S. argcnifa in this respect. 



"■A term defined by Bredcr (1967). 



Tabi.K 3.-DraK reduction by fish mucus, based on data from Rosen and 



(Cornford (1970, 1971). 



Species 



1 Salmo gairdneri Richardson 



(Rush Creek) 



2 S. gairdneri (Grant Lake) 



3 S. gairdneri (Lundy Lake) 



4 S. trutta Linneaus 



5 Sphyraena argentea Girard 



6 Scomber japonicus Houttuyn 



7 Sarda chiliensis (Culvier) 



8 Micropterus dolomieui Lac6p6de 



9 Pomoxis annularis Rafinesque 



10 Lepomis machrochirus Rafinesque 



11 Paralabrax clathratus (Girard) 



12 P. nebuliter (Girard) 



13 Parallchthys californicus (Ayres) 



493 



