Young arctic fish glow in the dark | Polarjournal
The lumpfish(Cyclopterus lumpus) is a bottom-dwelling fish found at depths from 50 to 800 meters. The fish belonging to the perch species grows up to 65 cm long and can weigh up to 9 kilograms. A total of 30 species of lumpfish are known. Image: TheSupermat CC BY-SA 3.0

A characteristic of young adolescents is to stand out from adults. At least with humans, this can be observed again and again. Fewer examples are known from the animal kingdom in this regard. But at least one example has been discovered by an Irish-British research team in a fish species that also occurs in the Arctic waters between Nunavut and Svalbard.

The lumpfish juveniles studied glowed neon green when Dr. Thomas Juhasz-Dora, a veterinarian and doctoral student at the University of Cork, Ireland, used royal blue spectral light on the animals and then photographed them with a digital camera and a special yellow filter. “I thought “Wow!”,” the researcher explained in an interview. The fish showed a strong biofluorescence response, which means that they probably glow like this at depth as well. The results of the study were published in the Journal of Fish Biology.

According to the research team, the glow is biofluorescent, which means that the animals do not cause it themselves. Rather, this form of glow occurs when the fish re-emit absorbed light (in this case, in the blue to ultraviolet range) at a lower wavelength (in this case, green). Biofluorescence is not to be confused with the other form of luminescence called bioluminescence, in which organisms have the ability to generate light. The research team also observed that different parts of the body glowed with different intensity. Especially the small tubercles at the edges and the lateral line of the otherwise scaleless fish shone strongly.

Some marine species are known to be biofluorescent. But most of them are found in tropical and subtropical waters and at greater depths. It is usually used for communication, predator avoidance, and attracting potential prey. Little evidence of biofluorescence is known from Arctic marine animals. Lumpfish are very remarkable in this respect, experts agree. The animals, which have a large range and occur from Spain to Svalbard, live at depths of up to 800 meters, but come close to the surface in summer to lay their eggs and fertilize them there. These are a popular delicacy and are also sold as “caviar of the north”. Lumpfish are also very popular in fish farms, where they keep fish lice at bay.

Why the animals glow is not yet clear. The research team suspects communication as the main reason. Furthermore, it is not yet clear whether the glow occurs in all developmental stages of the fish, whether there are sex-specific differences and whether the fish even possess the necessary tool to see the glow, i.e. a yellow filter in the intraocular cornea. This would at least provide another clue as to whether communication may indeed be the main reason for the glow in the dark of subarctic waters.

Dr Michael Wenger, PolarJournal

Link to study: Juhasz-Dora et al (2022) J Fish Biol 1-5 First record of biofluorescence in lumpfish (Cyclopterus lumpus), a commercially farmed cleaner fish;

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