Melanin-concentrating hormone is not involved in luminescence emission in the velvet belly lanternshark, Etmopterus spinax

Luminous deep-sea etmopterid sharks use hormonal control to regulate bioluminescence. Melatonin and prolactin trigger light emission and, conversely, alpha-melanocyte stimulating hormone actively reduces ongoing luminescence. Interestingly, these hormones are also known as regulators of skin pigment motion in teleost fish and epipelagic elasmobranchs. On the other hand, the melanin-concentrating hormone (MCH) is another regulator of the skin pigment motion in fish melanophores. Here, we studied the putative effect of MCH on the light emission control of the velvet belly lanternshark, Etmopterus spinax (Etmopteridae). In parallel, the presence of the MCH receptor in our model is investigated through database searches. Our results show that MCH is not involved in the bioluminescence triggering in the velvet belly lanternshark. Moreover, no MCH receptor transcript was found in a specific transcriptome of the luminous ventral skin of E. spinax.