A deepwater fish with ‘lightsabers’ – dorsal spine-associated luminescence in a counterilluminating lanternshark

Abstract

We report the discovery of light organs (photophores) adjacent to the dorsal defensive spines of a small deep-sea lanternshark (Etmopterus spinax). Using a visual modeling based on in vivo luminescence recordings we show that this unusual light display would be detectable by the shark's potential predators from several meters away. We also demonstrate that the luminescence from the spine-associated photophores (SAPs) can be seen through the mineralized spines, which are partially translucent. These results suggest that the SAPs function, either by mimicking the spines' shape or by shining through them, as a unique visual deterrent for predators. This conspicuous dorsal warning display is a surprising complement to the ventral luminous camouflage (counterillumination) of the shark.

Phylogeny and Taxonomy of Flatheads, Scorpionfishes, Sea Robins, and Stonefishes (Percomorpha: Scorpaeniformes) and the Evolution of the Lachrymal Saber

“…Recent studies (e.g., Sparks et al, 2014;Anthes et al, 2016;Gruber et al, 2016) have demonstrated that a number of fish groups have green and red fluorescence that appears to be playing an ecological and/or evolutionary role. As such, it is possible that the synanceiids could be advertising or highlighting this specialization with this fluorescence in a similar role as the bioluminescence associated with the defensive dorsal spines in etmopterid sharks (Claes et al, 2013) or that the lachrymal saber is involved in intraspecific competition and mate choice where synanceiid species are advertising their sabers to conspecifics.…”

New observations and ontogenetic transformation of photogenic tissues in the tubeshoulder Sagamichthys schnakenbecki (Platytroctidae, Alepocephaliformes)

“…The bioluminescence was found probably to be involved in reproductive signalling and counter‐illumination, the former being a possible trade‐off for the latter. The discovery of bioluminescence in fishes is ongoing, seen for example by a recent discovery of light organs associated with regularly examined dorsal‐fin spines in the common species E. spinax (Claes et al ., ) and in less frequently observed taxa such as the northern fat‐tail pencil smelt Nansenia boreacrassicauda Poulsen 2015 or the halosaur Aldrovandia oleosa Sulak 1977 (Poulsen, ; Poulsen et al ., ). Recent studies have shown that bioluminescence is likely to drive speciation (Alfaro, ; Claes et al ., ; Davis et al ., ; Ellis & Oakley, ).…”

Structure, composition, mechanics and growth of spines of the dorsal fin of blue tilapia Oreochromis aureus and common carp Cyprinus carpio

“…They are elongate structures with a high length-to-width aspect ratio, making them ideally suited to serve as the stiffening element for the hydro-dynamically functioning fin, similar to masts in a sail. Their conical shape, which ends distally in an extremely sharp free end, also forms an effective defence mechanism (Claes et al, 2013). The spine of C. carpio additionally possesses recurved serrations that are located on the caudal aspect of the distal third of the spine, similar to spines of Siluriformes (Trapani, 2008;Souza-Shibatta et al, 2013;Vanscoy et al, 2015), several fishes from the Tetraodontiformes and Gasterosteiformes (Bannikov & Tyler, 2006) and spines in the dorsal fin of some shark species (Maisey, 1979).…”