Body form and behavioural types in fish

Towards the end of the 19th century the characteristics of fish form aroused interest from a mechanical point of view. PARSONS1 examined the maximal cross sections of teleosts and cetaceans: a similar approach was taken by AMANS z who selected certain distinctive fishes for analysis. Earlier, the classic work of MAREY 3 demonstrated the element of anguilliform motion. A later notable study was that of HOUSSAY 4, who related body form to dynamic equilibrium: about the same time ALLIAUD and VL~S s also studied the natural stability of fish by an electrocutory technique. The literature is indeed somewhat diffuse, in that the problem of form belongs to no single discipline, and apart from the above investigations developmental studies need consideration, such as those of MEEK s, FULTON 7, and HECHT s. In this connection special mention must be made of Sir D'ARcv WENTWORTH THOMPSON s, and in particular of his application of the theory of transformations. He wrote: ' . . . i f . . .d iverse and dissimilar fishes can be referred as a whole to identical functions of very different co-ordinate systems, this fact will of itself constitute a proof that variation has proceeded on definite and orderly lines, that a comprehensive "law of growth" has pervaded the whole structure in its integrity, and that some more or less simple and recognizable system of forces has been in control.' x0 It is precisely by starting with a relatively undifferentiated type, such as the Salmonid, and applying the principles of (1) extension along a single axis, (2) tapering, (3) simple shear, and (4) the conversion of rectilinear into radial co-ordinates, that one may trace divisions and equations among fish forms, establishable by correlated behavioural or biological observations. MAGNAN'S excellent experiments n continued research along the lines of HOUSSAV, providing data on the dimensions of a large number of fish, on equilibrium, and on power of swimming. Meanwhile, in a completely different field, BREDER 12 examined the type of locomotion shown by particular species of fish, classifying it into anguilliform, ostraciiform, or carangiform. Later GREGORY 13 provided extensive classificatory schemata for the analysis of body form. Apart from the important work of GRAY 14-16, BAINBRIDGE 17,ls, and others, which considered locomotion per se, little explicit investigation was undertaken relevant to the problems of shape, neural organization, and behaviour as interconnected factors. A certain amount of evidence, however, may be gained from a consideration of mainly zoological studies, particularly those dealing with evolutionary questions such as the function of the tail and fins. Unfortunately, several Russian references relevant to this survey proved to be unobtainable, but they are listed below for completeness 19-z4. The sensitivities of the organism visual, olfactory, and tactile relate to morphology if they are to be developed in a given environment; this implies that they must be capable of increased performance; in other words, sensitivity precedes adaptation. A principle of concomitance is at work which ensures that when sensitivities are in the process of becoming attached to