558 SCHEVILL, BACKUS, AND HERSEY [CHAP. 14 



The frequency range of the squeals is not the same in all species, though 

 several of the few we know are not easily distinguished on this account. Globice- 

 phala (see Hersey, 1957, p. 265, fig. 11) has not only a lower squeal than 

 Delphinus, for example, but sings a markedly different song. 



8. Functions of Sound 



A . The Sexual Functions 



It has long been supposed that certain underwater sounds made by fishes 

 have a sexual significance. This supposition grew originally from observations 

 of that most noisy family of fishes, the Sciaenidae or drums, in which increases 

 in sound-production were noted at times of spawning. Indeed, in five out of 

 seven common genera of sciaenid fishes of northeastern America {Pogonias, 

 Sciaenops, Cynoscion, Leiostomus, and Bairdiella), it is only in the male that 

 the sound-making apparatus is developed. This is presumptive evidence that 

 the sounds of these fishes have a sexual function. (In the sciaenid genera 

 Menticirrhus and Micropogon the sound-producing mechanism is altogether 

 absent in the first case and is present in both sexes in the second.) Such observa- 

 tions in nature have been reinforced by observations in aquaria. Goode (1888) 

 cites data from the old New York aquarium in which specimens of the sea drum, 

 Pogonias cromis, produced sounds as male chased female in the spring. More 

 recently, Fish (1954) has found that the squeteague, Cynoscion regalis, held in 

 aquaria are more easily stimulated to sound-production during the approach 

 of the breeding season than at other times. 



A sexual function is probable for one class of sounds emitted by various 

 species of toad-fishes of the genus Opsanus (Fish, 1954; Tavolga, 1958b). In 

 Opsanus tau males establish a territory and guard a nest in which successive 

 females spawn. The male makes a loud "boat-whistle-like" sound at this time, 

 but ceases when his milt is spent (Fish, 1954). In the sea-robins (genus Prionotus) 

 the period of most active sound-production appears to be correlated with the 

 time of sexual maturity or its approach (Fish, 1954; Moulton, 1956). 



While such data as the foregoing do suggest sexual functions for certain 

 sounds it is not clear in most cases exactly how a given sound serves to accom- 

 plish the union of the sexes. Sound might serve to bring widely separated 

 individuals of opposite sex near one another, it might serve for sexual recogni- 

 tion in a group already assembled, or it might be used at stages in the courtship 

 or spawning procedures. It is from the last category that come the least equi- 

 vocal observations. 



In the so-called purring gourami, Trichopsis vittatus, both sexes produce a 

 sound during the prespawning behavior (Stampehl, 1931 ; Beyer, 1931 ; 

 Reickel, 1936). Clicking sounds are produced by both male and female sea- 

 horses {Hippocampus spp.) during the preliminaries to spawning and especially 

 during the act itself, when "loud and continuous" sounds are made as the 

 female deposits eggs in the brood pouch of the male (Dufosse, 1874; Fish, 

 1954). In the filefishes, Cantherines pulles and Alutera punctata, the large dorsal 



