Fish with red fluorescent eyes forage more efficiently under dim, blue-green light conditions

Abstract

BackgroundNatural red fluorescence is particularly conspicuous in the eyes of some small, benthic, predatory fishes. Fluorescence also increases in relative efficiency with increasing depth, which has generated speculation about its possible function as a “light organ” to detect cryptic organisms under bluish light. Here we investigate whether foraging success is improved under ambient conditions that make red fluorescence stand out more, using the triplefin Tripterygion delaisi as a model system. We repeatedly presented 10 copepods to individual fish (n = 40) kept under a narrow blue-green spectrum and compared their performance with that under a broad spectrum with the same overall brightness. The experiment was repeated for two levels of brightness, a shaded one representing 0.4% of the light present at the surface and a heavily shaded one with about 0.01% of the surface brightness.ResultsFish were 7% more successful at catching copepods under the narrow, fluorescence-friendly spectrum than under the broad spectrum. However, this effect was significant under the heavily shaded light treatment only.ConclusionsThis outcome corroborates previous predictions that fluorescence may be an adaptation to blue-green, heavily shaded environments, which coincides with the opportunistic biology of this species that lives in the transition zone between exposed and heavily shaded microhabitats.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-017-0127-y) contains supplementary material, which is available to authorized users.

Controlled iris radiance in a diurnal fish looking at prey

“…Previously, we found that red fluorescent irides are most prevalent in small fish feeding on small, eyed prey [20], hinting at the possibility that light emission from the iris may constitute a visual aid in detection [21]. Indeed, one of those species captured more prey under "fluorescent-friendly" conditions in a subsequent experiment [22], even though the contribution of active photolocation to this finding remains to be shown.…”

“…Specifically, we test the hypothesis that light radiated from the iris is up-or down-regulated in response to the environmental context. Since up-and down-regulation of fluorescence is slow [18,23] and therefore hard to quantify in freemoving individuals, we focus on the ocular spark, a bright spot on the iris, just below the pupil (figure 1, [19][20][21][22][23][24]. Ocular sparks are produced by the protruding spherical lens (figure 2a) which allows downwelling light to cross without entering the pupil, a feature of most bony fish species.…”

Do the fluorescent red eyes of the marine fish Tripterygion delaisi stand out? In situ and in vivo measurements at two depths

“…Although fluorescent pigments are widespread in benthic marine organisms (Alieva et al., ; Eyal et al., ; Marshall & Johnsen, ; Sparks et al., ), their presence in fish living in shallow water (0–40 m) has only recently been confirmed (Anthes et al, ; Gerlach et al, ; Michiels et al., ; Sparks et al., ). To date, several studies investigated potential functions of red fluorescence in fish, including intraspecific communication, camouflage, and prey detection (Anthes et al., ; Detecting the Detector; Harant & Michiels, ; Meadows et al., ). In this study, however, we only focus on assessing whether such a red signal stands out in front of natural backgrounds and thus generates a perceptible contrast.…”

Does red eye fluorescence in marine fish stand out?In situandin vivomeasurements at two depths

“…Anthes et al [12] also found that the presence of conspicuously red fluorescent irides seems to be associated with a micro-predatory lifestyle [5, 13]. Moreover, a recent experimental study indicated that foraging success increases under dim, “fluorescence-friendly” cyan illumination relative to broad spectral illumination at the same brightness in the triplefin Tripterygion delaisi [14].…”