Image: Black Marlin fin ray base

Black Marlin fin ray base

Fin base of the marginal (leading) ray of a billfish, probably a Black Marlin.  The bone was found by Harry Rosenthal on Backwoods Beach, Cronulla (directly opposite Shark Island), New South Wales on 4 August 2012. The bone was lying on the sand in its current 'clean' state. No other bones were found in the vicinity.

Mark McGrouther
© Australian Museum


Black Marlins have rigid pectoral fins that have a very limited range of movement.  Part of this rigidity results from the flat basal surface of the leading pectoral fin ray which sits against the flat surface of the scapula. Other billfishes, such as the Blue Marlin, have a markedly convex pectoral fin base that allows the fin to be moved.


Wapenaar, M.-L. & F.H. Talbot. 1964. Note on the rigidity of the pectoral fin of Makaira indica (Cuvier). Annals of the South African Museum. 167-180.

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Tags pectoral fin, ray, bone, wash up, beach, black marlin, Istiophoridae, Makaira indica,