Acoustic communication in the Teleostei has been studied extensively over the last six decades [1–5]. By 1981, Myrberg  had documented sound production in more than 30 families, including: Batrachoididae, Carangidae, Scianidae, Holocentridae, and Serranidae. More recently, sounds were recorded in additional taxa, such as Carapidae , Ophidiidae [8, 9], Chaetodontidae [10, 11], Oplegnathidae , and Sebastidae . Communication sounds are now estimated to occur in as many as 109 teleost families . Of note, these discoveries of fish acoustic communication have provided new examples of an increasing diversity of fish sound-producing mechanisms [15, 16] that contrast with the relatively conserved mechanisms of sound emission in other vertebrate classes .
In addition to descriptions and identification of fish calls, several studies have examined how abiotic and biotic factors influence sound characteristics. Temperature affects sound production in many species, increasing the contraction rate of sound-producing muscles [18, 19]. In Cynoscion regalis, higher temperatures increase pulse rate, call intensity, and the dominant frequency of the sound . Similar effects on sound were also demonstrated in Opsanus tau and Ophidion marginatum. In the catfish Platydoras armatulus, the dominant frequency and, to a lesser extent, pulse period of drumming sounds were affected in a comparable manner . Muscle features can influence sound characteristics as well. Differences in muscle length can cause changes in sound characteristics between juveniles and adults because of a body size-related scaling effect [24, 25]. The twitch contraction time was found to rise with increasing body size in a salamander , lizard , and fish . Besides size effects, the sound-generating mechanism of many fishes, especially the sonic muscles, is also sexually dimorphic . In sciaenid species such as Micropogonias undulatus, the sonic muscles and associated swimbladder are larger in males [27, 28]. In other species of the family, however, drumming muscles are completely lacking in females [27, 28]. In three sciaenid species investigated by Hill, sonic muscles form before or during puberty depending on the species . In the Batrachoididae, Opsanus tau and Porichthys notatus[30, 31], sexual dimorphism of sonic muscles is quite pronounced. In both species, sonic muscles are present in small juveniles [31, 32] and differences observed in adult morphotypes are caused by differences in fiber growth rates and proliferation [29, 31]: sonic muscles become bigger in males [29, 31]. In addition, some fish species display a hypertrophy of sonic muscles during breeding season [33, 34]. In weakfish, this hypertrophy results in the emission of sounds with higher intensities, lower frequencies, and longer pulse durations .
According to Nielsen et al. , Ophidiiformes comprises four families: Ophidiidae, Carapidae, Bythitidae, and Aphyonidae. Ophidiidae [36, 37], Carapidae  and Bythitidae [38, 39] are hypothesized to be soniferous fish based mainly on their morphology. Sounds were, however, recorded in five carapid species [7, 40, 41] and in two species of Ophidiidae [8, 9, 22].
Ophidiiformes present an extraordinary variety of highly specialized structures associated with sound production [2, 9, 37, 42–45]. Moreover, the sonic mechanisms of Ophidiidae are characterized by pronounced sexual dimorphisms [36, 37, 42, 45, 46]. They are generally composed of modified thoracic vertebrae, one to three pairs of sonic muscles, and a highly modified swimbladder. In some species, the anterior part of the swimbladder forms a so-called ‘rocker bone’ [42, 43, 46, 47] on which sonic muscles insert [9, 16, 42, 43]. This structure is likely involved directly with sound production, as its movement deforms the swimbladder wall [2, 9, 16]. It is present in adult males of some Ophidion but not in females or in juveniles [42, 46]. A rocker bone was also reported in carapids of the genus Onuxodon[2, 48], but its presence in both sexes was not investigated. Sexual dimorphisms of sonic mechanism have been documented in many Ophidiidae, but sounds have only been recorded from males of two species. Thus, the associated influence of sex specific morphology on sound emission has not been determined.
The present work focuses on Ophidion rochei, an endemic species living in Mediterranean and Black Seas . This species inhabits coastal shallow waters  but little is known about its biology because it is nocturnal and hides during daylight hours in the sand [50–52].
Because of its nocturnal habits, Ophidion rochei may provide insight on the evolution of acoustic communication in environments where available light limits visual communication. Moreover, most ophidiiform species inhabit deep seas  and thus may experience similar evolutionary selection pressures associated with living in a dark environment. Consequently, an understanding of the biology of sound production in O. rochei may provide important framework for hypotheses in future studies on acoustic communication in deep sea species.
The aims of this paper are: 1) to determine the different sonic apparatus morphotypes in this species 2) to obtain and describe sounds for each morphotype, and 3) to investigate the relationship between morphology, sound characteristics, and ecological niche in O. rochei.