30 



A HISTORY OF FISHES 



swimming, but one or two species depart from this normal 

 attitude. The vertical position of the Sea Horse [Hippocampus) 

 has been already mentioned. The little Shrimp-fishes or 

 Needle-fishes [Centriscidae) are curious creatures, with the long 

 compressed body encased in a thin bony cuirass with a knife- 

 like lower edge. One species found in the Indian Ocean lives 

 in small shoals of about half a dozen individuals, and normally 



swims about in a vertical 



position with the long tube- 

 like snout pointing upwards 

 (Fig. 12). On occasions, how- 

 ever, it has been observed 

 to move in the normal hori- 

 zontal attitude, and even 

 vertically, but upside down ! 

 A Cat-fish from the Nile and 

 other African rivers (Syno- 

 dontis batensoda) has adopted 

 the remarkable habit of 

 floating or swimming leis- 

 urely at the surface of the 

 water with the belly upwards^ 

 an attitude taken up by no 

 other fish unless it be sick or 

 dead. This habit must have 

 been well known to the ancient 

 Egyptians, as it is frequently 

 depicted in their sculptures 

 and wall paintings in this 

 anomalous position. 



Among the methods of 

 locomotion other than swim- 

 ming, leaping and burrowing may be considered briefly here, as 

 they result from body rather than fin-movements. A fish may leap 

 out of the water for one of several reasons : to escape from an 

 enemy, to clear a weir or other obstacle, or from pure joie de 

 vivre. The strength and agility displayed by the Salmon (Salmo) 

 (Fig. 13c) in leaping falls in its journey to the spawning ground 

 is well known, and it has been observed to make repeated efforts 

 to clear an obstacle which was too high for it, and to fall back 

 at last through sheer exhaustion. It is this habit which has given 

 the Salmon its name, the Latin Salmo being from the same root 

 as salire^ to leap. The Tarpon (Megalops), a favourite with 



Fig. 12. — A FISH WHICH SWIMS UPRIGHT. 



A small shoal of Shrimp-fishes (AeoHscus 

 strigatus), X ^. (After Willey.) 



