FISHERY BULLETIN: VOL. 74, NO. 3 



that the lateral line is important in schooling 

 behavior." In the same publication Walters and 

 Liu (1967) ". . . postulate that the boundary layer 

 acts as a hydrodynamic amplifier . . ." that is 

 involved in transferring precise information on 

 changes in w^ater movement that the fish en- 

 counters as it swims ahead, reaching the fishes 

 brain via the lateral line system. In a school, much 

 of such information concerns the water 

 movements produced by the swimming activities 

 of the fishes ahead, probably by the bending of the 

 cupulae that indicate the direction of flow of the 

 currents and its strength. Other experiments 

 carried out by different investigators point the 

 same way as, for instance, the work of Pitcher 

 (1973) with mirrors. This is not in discord with the 

 related work reported here and both can be ac- 

 counted for by the effects of the lattice pattern and 

 the hydrodynamic and the mucus cues. Also the 

 work of Shaw and Tucker (1965) and the interpre- 

 tation of their results by van 01st and Hunter 

 (1970), based on an optomotor device, indicated 

 that the test fish reacted more to the fishes ahead 

 of it than to the moving target spot. 



Another source of possible information has been 

 pointed out by Smith (1930) in some little-noticed 

 studies. These have shown that Carassius auratvs 

 (Linnaeus) can draw samples of the surrounding 

 water into its lateral line canals and expel them as 

 new samples are drawn in. This behavior certainly 

 suggests the possibility of a chemical or other 

 sensory device that could distinguish the concen- 

 tration of the mucus of preceding fishes. Present 

 understanding of the relation of the sensory 

 possibilities related to schooling organization 

 clearly suggests that such activity of the lateral 

 line could be a part, or even an important element, 

 in a following fish's ability to locate the most 

 favorable position to be stationed in respect to the 

 mucus of the preceding individual. 



Fish at the front of a school receive locomotor 

 benefits from only their own production of mucus. 

 All the rest receive benefits from the mucus of 

 those ahead; those at the very end of a school thus 

 receive the most benefit. This is sufficient to 

 account for the "churning" sometimes seen in 

 schools, the leaders falling back while others press 

 ahead, all of which helps maintain the integrity of 

 the school as previously noted. 



The peripheral individuals in a school often keep 

 trying and usually do eventually attain a more 

 central position, evidently for reasons similar to 



those given above. The rapid reorganization of a 

 school after violent disruption is apparently 

 similarly motivated. 



The existence of fish mills, as noted in the prior 

 section, may not be the trivial phenomenon it is 

 generally thought to be. Instead, in the present 

 view, it may be a resting device with an important 

 purpose. If the fishes reach a point of fatigue that 

 would slow the school down to an extent inimical to 

 the schools integrity, the mill formation would 

 supply that necessary respite. 



All three of the preceding observable items of 

 activity, as noted, have a consolidating effect on a 

 school and none show any tendency toward school 

 dispersion. 



The works of Belyaev and Zuev (1969), Zuev and 

 Belyaev (1970) and Weihs (1973a) discussed the 

 hydrodynamic effects of one fish on another in a 

 school, considering only the water movements 

 induced by the swimming efforts of each member 

 of the school. This is all in basic agreement with 

 the present theoretical treatment of the school 

 organization. Adding to this, the effects of the 

 drag reducing abilities of the mucus released by 

 the fishes involved can only result in much higher 

 efficiency. 



Furthermore, there is no evidence that more 

 mucus cannot be released by fishes to ease their 

 muscular efforts when necessary. There are, 

 however, strong probabilities that such abilities 

 are indeed present. Species that use their mucus 

 for other purposes have this faculty developed to 

 a high degree, as in Rypticus (Maretzki and del 

 Castillo 1967), that exudes a toxic mucus in great 

 quantities when attacked or handled or many of 

 the parrotfishes that envelope themselves in a 

 "cocoon" of congealed mucus on nightfall (Winn 

 1955). Quality control is also possible with many 

 fishes under appropriate stimulation. All calcula- 

 tions at this time involving mucus production are 

 somewhat uncertain and must remain so until it is 

 known whether the mucus is exuded at a rather 

 steady rate or is subject to wide fluctuations, 

 somewhat after the manner of perspiration in 

 various mammals. 



It is possible that the closing up of ranks, when a 

 school is in flight from some danger, may destroy 

 the assistance of both vortices and mucus. Under 

 this kind of emergency, involving maximum en- 

 ergy expenditures, this loss may have to be ac- 

 cepted. Possibly such a situation could call for an 

 extra outpouring of mucus. 



498 



