Belgian scientists have discovered the hormonal mechanism by which the velvet belly lantern shark (Etmopterus spinax) controls its luminescence, making it the first instance of hormonal control of bioluminescence in fishes.
Publishing their research in a recent issue of the Journal of Experimental Biology, Julien Claes and Jrme Mallefet identified melatonin, prolactin and a-melanocyte-stimulating hormone (MSH), hormones known to control pigmentation in sharks, as the key substances in controlling bioluminescence in lantern sharks. Bioluminescence is controlled by nerve cells in other fishes.
Lantern sharks get their name from their bioluminescent abilities, possessing light-emitting photophores on their flanks and abdomen.
It is thought that the bioluminescence serves to protect the sharks from predators via counter-illumination and is also possibly used in social interactions.
The authors injected patches of skin from the bellies of freshly killed lantern sharks with various neurotransmitters and hormones and discovered that melatonin and prolactin stimulated while a-MSH inhibited bioluminescence.
The researchers also found that melatonin induced a slower, longer-lasting glow while prolactin induced a faster, quicker glow.
They hypothesize that the slower glow induced by melatonin could be very convenient for vertical migrations during which the ambient light intensity may increase/decrease gradually (matching the intensity of downwelling light with its luminescence is particularly convenient for camouflage by counter-illumination), while the faster, quicker glow induced by prolactin might be useful for schooling, mating or predator escape.
For more information, see the paper, Claes, JM and J Mallefet (2009) Hormonal control of luminescence from lantern shark (Etmopterus spinax) photophores. Journal of Experimental Biology 212, pp. 3684"3692.