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Environ Biol Fish (2009) 86:427441 DOI 10.1007/s10641-009-9543-y
Why is the neon tetra so bright? Colorationfor mirror-image projection to confuse predators? Mirror-image decoy hypothesis
Takehide Ikeda & Shiro Kohshima
Received: 20 October 2008 /Accepted: 7 October 2009 /Published online: 23 October 2009 # Springer Science + Business Media B.V. 2009
Abstract The neon tetra (Paracheirodon innesi), which inhabits blackwater streams of the Amazon basin, has extremely bright coloration characterized by metallic blue-green stripes. To clarify the ecological function of this coloration, we examined the appearance of living neon tetra. They changed color in response to lighting and background conditions, and became less conspicuous under each condition to the human eye. Although they appeared bright in colorless clear water, their stripes appeared darker in blackwater. In addition, the visible area of their stripes was small and their brightness decreased, unless they were observed within a limited viewing angle (approximately 30 above the horizon). The results show that from the viewpoint of approaching submerged predators, a bright mirror image of the stripes is projected onto the underside of the waters surface, providing a dramatic visual target while the real fish remains less conspicuous. Based on these results, we
hypothesize that the neon tetras bright coloration is an effective predator evasion strategy that confuses predators using bright mirror images.
Keywords Anti-predation . Camouflage . Iridophore . Aposematic
Abbreviations the angle between the horizontal and the line of measurement/sight
Introduction
The neon tetra (Paracheirodon innesi; Myers 1936) is a small characin with bright coloration that inhabits blackwater streams of the upper Amazon basin (Gry 1966). A popular aquarium fish, it is characterized by remarkably bright body coloration, particularly an iridescent blue-green lateral stripe along both sides of the body that extends from the iris to the caudal peduncle. Weizman and Fink (1983) noted that while body stripes are common in other characids, they are never of the intensity found in Paracheirodon.
The physiological structure and characteristics of the iridescent chromatophores (iridophores) in the body stripe have been studied (e.g. Clothier and Lythgoe 1987; Nagaishi et al. 1990; Oshima and Nagaishi 1992), and the stripe appears to be capable
T. Ikeda (*)
Graduate school of Bioscience and Biotechnology, Tokyo Institute of Technology,2-12-1 WA-43, Ookayama, Meguro-ku,Tokyo 152-8551, Japane-mail: [email protected]
S. KohshimaWildlife Research...