INTRODUCTION
The genus Elacatinus Jordan 1904 currently contains 24 valid species (Eschmeyer and Fricke, Reference Eschmeyer and Fricke2014); all but the Elacatinus puncticulatus (Ginsburg, Reference Ginsburg1938), which is from the eastern Pacific, occur on the western Atlantic (Van Tassell, Reference Van Tassell, Patzner, Van Tassel, Kovačić and Kapoor2011), and three of which are endemic to Brazilian waters. Generally, Elacatinus species are small brightly coloured reef inhabitants that feed mainly on parasites by engaging in cleaning symbiosis with larger fishes and invertebrates (Pezold, Reference Pezold1993; Sazima & Moura, Reference Sazima and Moura2000; Sazima et al., Reference Sazima, Sazima, Francini-Filho and Moura2000, Reference Sazima, Krajewski, Bonaldo and Sazima2004). They have recently been used as models for speciation studies on large versus small geographic scales (Colin, Reference Colin2003; Palumbi & Warner, Reference Palumbi and Warner2003; Warner & Palumbi, Reference Warner and Palumbi2003; Taylor & Hellberg, Reference Taylor and Hellberg2005) and connectivity (Colin, Reference Colin2010), presenting such high speciation rates that they have yielded a comparison with Tolkien's Hobbits (Palumbi & Warner, Reference Palumbi and Warner2003) due to their low mobility and phylopatric behaviour.
The evolution of different reef fish colour morphs, as well as how they are generated and maintained in natural populations, is poorly understood. Colour polymorphisms are particularly common among reef fishes (Randall & Randall, Reference Randall and Randall1960), but despite the number of studies concerning behaviour and long hours of underwater observation, there is no report on an Elacatinus figaro white morph.
MATERIALS AND METHODS
The present observation and collection was made in January 2013 at Ilha Grande, Rio de Janeiro State, Brazil (23°06′34″S 44°15′58″W), a subtropical region on the Brazilian south-eastern coast.
The bottom was approximately 6 m deep, composed mainly of large rocks covered by calcareous algae, ascidians, bryozoans, as well as a great variety of sponges and zoanthids – predominantly Palythoa carybaeorum. The locality was a cleaning station visited by a Chaetodon striatus during the observation period. Surrounding the cleaning station, some individuals of Abudefduf saxatilis, Pomacanthus paru, Mycteroperca acutirostris, Diplodus argenteus and Dactylopterus volitans were observed. The capture was made with hand nets and the specimen was deposited at the Museu Nacional Ictiological collection under the catalogue collection number MNRJ41650.
RESULTS
We collected, for the first time, an Elacatinus figaro white morph (Figure 1A) during a SCUBA dive. The specimen was 24.8 mm in standard length and was captured at a cleaning station, at a depth of approximately 6 m, along with other regular-coloured specimens (Figure 1B).
(A) Elacatinus figaro white morph; (B) E. figaro white morph alongside other regular-coloured specimens.
The sampled individual showed a regular black colour and the absence of its yellow pigment revealed a white stripe that can also be seen as blue, depending on the light's angle of incidence.
DISCUSSION
The occurrence of colour morph variations has been documented for some species of reef fishes, such as Serranidae (Graves & Rosenblatt, Reference Graves and Rosenblatt1980; Medioni et al., Reference Medioni, Leconte Finiger, Louveiro and Planes2001), Cirrhitidae (DeMartini & Donaldson, Reference DeMartini and Donaldson1996), Syngnathidae (Guimarães, Reference Guimarães1999), Ostraciidae (Pattengill-Semmens, Reference Pattengill-Semmens1999), Pomacentridae (Planes & Doherty, Reference Planes and Doherty1997) and Pomacanthidae (Lubbock & Edwards, Reference Lubbock and Edwards1981; Colin, Reference Colin1982; Luiz-Júnior, Reference Luiz-Júnior2003).
Although we report here for the first time the Gobiidae Elacatinus figaro white morph, recently, L. Rocha (personal communication) reported the sighting of another specimen at Paraíba State, Brazil around 1995, suggesting that the morph is not as uncommon as it seems.
Carotenoid pigments are responsible for most of the yellow colouring in species, but animals are unable to synthesize them – they must acquire them, intact, from their diet (Goodwin, Reference Goodwin1984). Since the white morph lived at a cleaning station with many other regular-coloured individuals, we assume that this fish did not have any problems in acquiring carotenoids from their diet, being more parsimonious, with the belief that a mutation somewhere along the enzymatic pathway that incorporates the carotenoids is responsible for the lack of yellow pigment. The strong bright yellow colour is of vital importance for attracting other fish to the cleaning station, and since E. figaro is a specialized cleaner that consumes ectoparasites from other fish as its main source of food (Sazima et al., Reference Sazima, Moura and Rosa1997), we speculate that it is opportunistic in living alongside regular-coloured morph individuals that attract clients to the cleaning station.
ACKNOWLEDGEMENTS
The authors would like to thank Luiz A. Rocha for providing information about the white specimen observed at Paraiba in the 1990s and Abudefduf Atividades Subaquáticas for logistic support during fieldwork. The study was supported by CAPES’ grant number 2346/2011 (PNPDinstitucional) and CNPq.
