The blacksail snake mackerel (Thyrsitoides marleyi) known also as the black snoek, is a species of snake mackerel found throughout the Indo-Pacific and West Pacific at depths up to 400 metres (1,300 ft) where they appear to prefer slopes on seamounts and ridges. They are known to make diel vertical migrations to the surface at night. This species reaches a length of 200 centimetres (79 in) TL though most do not exceed 100 centimetres (39 in) SL. This species is of minor importance to local commercial fisheries. Since it is at present the only known member of the genus Thyrsitoides, that genus is said to be monotypic.