Introduction

The concept that animals typically communicate in networks (involving at least one signaller and more than one receiver) derives from the active space of signals and social spacing of conspecific and heterospecific receivers (McGregor & Peake, 2000; Ch. 1). The ecological and evolutionary consequences of such networks have been explored most thoroughly for visual (e.g. Ch. 12) and acoustic signals (e.g. Otter et al., 1999; Ch. 2), although it is clear that chemical signalling also can involve networks (Chs. 11 and 16). Research on aquatic communication networks has so far been limited to the context of visual and acoustic signalling (e.g. Oliveira et al., 1998; Chs. 5 and 18). Semiochemicals (i.e. chemicals that transfer information within and/or between species) exert important and diverse effects on the behaviour and physiology of aquatic animals (Liley, 1982; Chivers & Smith, 1998; Kats & Dill, 1998; Sorensen & Stacey, 1999; Stacey & Sorensen, 2002; Wisenden, 2003). Studies of two key aspects of fish chemical ecology (predator–prey and reproductive interactions) have revealed great differences in the sources and nature of the semiochemicals released, their active spaces and their biological functions. These studies also provide sufficient information to assess, in fish, the existence and function of semiochemical information networks, which we define more fully below as a general category of network that includes not only communication networks employing specialized signals but also other networks employing unspecialized cues.