Environmental Biology of Fishes 66: 231–236, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. Male courtship sounds in a teleost with alternative reproductive tactics, the grass goby, Zosterisessor ophiocephalus Stefano Malavasi 1,∗ , Patrizia Torricelli 1 , Marco Lugli 2 , Fabio Pranovi 1 & Danilo Mainardi 1 1 Dipartimento di Scienze Ambientali, Campo della Celestia 2737/b Universit ` a Ca’ Foscari di 30122 Venezia, Italy (e-mail: mala@unive.it) 2 Dipartimento di Biologia Evolutiva e Funzionale, Universit` a di Parma, Viale della Scienze, 1-43100 Parma, Italy Received 3 December 2001 Accepted 16 June 2002 Key words: sound structure, dominant frequency, amplitude, acoustic behaviour Synopsis Male grass gobies show two alternative breeding tactics, territorial and sneaker, distinguished by body size and difference in ray elongation on the second dorsal fin. The larger males, with elongated fins, are territorial and emit sounds during courtship. Smaller males, without elongated fins, act as sneakers. Both large and small males produce sounds in the presence of a ripe female. Males produce a grunt, lasting about 300 ms, made up of pulses repeated at a low rate (22–68pps). Pulse duration, number, and repetition rate, did not differ between the two male types, but dominant frequency and sound amplitude did. Dominant frequency had a strong, inverse relationship with body size, whereas sound amplitude showed a weak positive relation to body size. Male size, and not the particular reproductive male tactic employed, is the most important correlate of sound properties in this species. Introduction The literature on the origin and evolution of alternative tactics and strategies in fishes is abundant (reviewed in Taborsky 1994). However, few studies have exam- ined the structure, use and function of signals (mainly visual) by males adopting different strategies or tactics. The use of sounds in the context of sexual or aggressive communication has been widely documented among fishes (reviewed in Fine et al. 1977, Hawkins & Myrberg 1983). Sound properties, such as amplitude or spectral composition, have been found to be related to body size in several species (Takemura 1984, Lobel & Mann 1995, Myrberg et al. 1993). In species with plas- tic tactics, factors other than body size may affect the expression of secondary sexual traits (Oliveira & Almada 1998, Grober 1997), including sounds (Brantley et al. 1993). Aspects such as the facultative use of acoustic signals or their structural changes across ontogeny have been poorly investigated among these species. The plainfin midshipman Porichtys notatus is the only teleost where the acoustic signals emitted by different types of males have been thoroughly inves- tigated. Males of this species adopt alternative repro- ductive strategies and display divergent development of the acoustic communication system (Bass 1992). Within the large and diverse family Gobiidae (Teleostei), the occurrence of alternative tactics (Cole 1982, Magnhagen 1992, Mazzoldi et al. 2000, Torricelli et al. 2000, Malavasi et al. 2001) and sound communication (Tavolga 1958, Mok 1981, Takemura 1984, Torricelli et al. 1990, Lugli et al. 1997, Lindstrom & Lugli 2000) have been docu- mented in many species. The grass goby, Zosterisessor ophiocephalus, is a burrowing species, inhabiting the sea grass meadows of shallow brackish waters along the coasts of Mediterranean and Black Sea. The breeding male of this species produces grunt-like sounds asso- ciated with territorial defence and courtship behaviour (Casaretto et al. 1988). The grunt emitted during fight- ing is often followed by a ‘staccato’ sound (Casaretto 1988). Available evidence strongly indicates the pres- ence in this species of a conditional reproductive strat- egy consisting of two types of male, distinguishable