Marine fishes, like other vertebrates, have a complex and highly
specialized eye (Marshall 2000). The eyes of over 70 species of
marine fishes have been analysed and have at least two different
types of cone cells (Marshall et al. 2006). Multiple types of cone
cells are a requirement for colour vision (Siebeck et al. 2008). Five
distinct types of photopigments have been isolated from the eyes of
coral reef fishes: ultra-violet-sensitive, violet-sensitive, bluesensitive,
green-sensitive, and red-sensitive (Munz & McFarland
1975; Loew & Lythgoe 1978; Levine & MacNichol 1979; Lythgoe
et al. 1994; McFarland & Loew 1994). Based on this evidence,
many coral reef fishes are physiologically capable of colour vision,
although some may only be able to distinguish between two
colours, while others may distinguish three or more (Marshall
2000).
Bluehead wrasses, like all coral reef fishes, live in one of the
world’s most colourful ecosystems. Colourful fishes and invertebrates
act as habitat, food and predators, with the full spectrum of
visible colours represented among animals as diverse as sponges,
cnidarians, molluscs and fishes (Feddern 1965; Pawlik et al. 1995).
Conspecific fishes are well understood to signal social dominance
and mate attraction by changing body colour (Warner & Swearer
1991).