Shining in the dark: First record of biofluorescence in the seahorse Hippocampus reidi

Abstract

Marine environments are visual domains restricted regarding light characteristics. Overall, blue monochromatic spectrum prevails in offshore areas especially below 15m depth, since long wavelengths are quickly attenuated. Light intensity is even more constrained in coastal waters, particularly those of tropical estuaries and bays, because further scattering through dissolved and suspended materials. Biofluorescence, which is the ability of organisms to absorb light and reflect it in a different wavelength, has been reported for many marine fish. In this paper, biofluorescence was recorded for the first time for the longsnout seahorse Hippocampus reidi , under natural conditions at Ilha Grande bay, Brazil, and both adult, juvenile and fry individuals kept in captivity. Although displaying the same colour emissions, seahorses differed in relation to body lighting, colour patterns, and age wherein fluorescence occurs. Newborn seahorses exhibit green biofluorescence only in the eyes and stomach. Further experiments are necessary to address whether H . reidi can change the patterns of biofluorescence emission for sensorial and social purposes.

First detection of biofluorescence in a deep‐sea anglerfish

“…Additionally, it is observed across various habitats, occurring in shallow tropical coral reef fishes (Michiels et al ., 2008; Sparks et al ., 2014), species that inhabit sandy or rubble habitats (Miyamoto et al ., 2020) and arctic fishes (Gruber & Sparks, 2021). Green is the most common fluorescent emission in fishes, although yellow, orange and red also occur (Gruber et al ., 2016; Michiels et al ., 2008; Sparks et al ., 2014), and some species will fluoresce multiple colours (Gruber & Sparks, 2021; Vaccani et al ., 2019). Biofluorescence is also found in species that occur at greater depths, where the blue light spectrum may be limited, precluding ambient fluorescence from occurring (Sparks et al ., 2014).…”

Diversity of Seahorse Species (Hippocampus spp.) in the International Aquarium Trade

“…Large seahorse species that are commonly fished, such as H. reidi (Figure 3b), are overall less specific in their habitat requirements but share several traits with small congenerics, such as the use of camouflage and an immobile body posture while using the tail as holdfast [29,108] (Figure 3b), but some species are able to change coloration as part of their courtship behavior [109,110] or need for camouflage [103]. A few species are exceptional and show much interspecific variation in coloration, including bright tints [29,111] and biofluorescence [96,112]. Various large seahorse species are commonly found in seagrass beds [113][114][115][116][117][118], and as they can be monitored easily by recreational divers as citizen scientists [119], they can also be handpicked by professional fishermen.…”

First record of biofluorescence in lumpfish (Cyclopterus lumpus), a commercially farmed cleaner fish

“…This variance is a result of scattering from the water itself or by suspended particles within the water body or absorption by particles (Jerlov, 1968 ). Marine organisms absorb the ambient blue light (450–495 nm) present in their environment generally via fluorescent compounds, reemitting green (495–570 nm), orange (590–620 nm) and red (620–750 nm) fluorescence into their environment (Gruber & Sparks, 2021 ; Vaccani et al ., 2019 ). The shorter wavelengths (blue, green) can penetrate to deeper depths, whereas longer wavelengths (orange, red) are quickly attenuated in depths >15 m (Kirk, 2011 ).…”

“…The unique lighting conditions produced by this spectrally restricted (blue‐shifted) illumination allow marine organisms to exploit fluorescence to produce visual contrast and patterns (Gruber et al ., 2016 ; Gruber & Sparks, 2021 ; Sparks et al ., 2014 ). Biofluorescence in marine teleost fish may function for communication, predator avoidance or prey attraction in otherwise cryptic species (Gruber & Sparks, 2021 ; Vaccani et al ., 2019 ; Sparks et al ., 2014 ). Biofluorescence appears particularly common and phenotypically variable in tropical fish communities (Anthes et al ., 2016 ; Gerlach et al ., 2016 ; Gruber & Sparks, 2021 ).…”

“…( 2014 ) reported green fluorescence covering the entire body of varying fish species, whereas Vaccani et al . ( 2019 ) documented the green fluorescence concentrations around the head, eyes and upper trunk of the diurnal seahorse Hippocampus reidi . Green fluorescence may be related to prey attraction, as has been documented through the attraction of juvenile Sebastes rockfish to green hydromedusa tentacles under excitation lighting (Haddock & Dunn, 2015 ; Vaccani et al ., 2019 ).…”