Today’s blog is based on the little-known ‘southern ocean sunfish’, less commonly known as Mola ramsayi. The southern ocean sunfish has a bit of a raw deal, often outshone by its famous sibling species Mola mola, which is confusingly, (and somewhat arrogantly) known as the ocean sunfish… but now it’s time for the Southern Sunfish to shine!!
Photo of Mola ramsayi stranded on shallow waters in Port Phillip Bay, Victoria. (Image credit; Martin Gomon, made available through Wikimedia Commons)
Originally, when M. ramsayi was first described, it was suggested to only occur in the Southern Hemisphere (hence the common name), but since then individuals have been spotted in the Northern Hemisphere too, including the Sea of Oman, the Indian waters of Chennai and co-occurring with M. mola.
Superficially, Mola ramsayi looks a lot like Mola mola, but there are a few ways to tell them apart without resorting to genetic analysis. Polish up your specs and have a closer look at that funny tail; the clavus. Firstly, we need to look at the fin rays. These act as skeletal support, fanning out the clavus, which acts as a rudder to steer the fish and guide its movements; M. ramsayi has 16 fin rays, whereas M. mola only has 12 . Aside from the rays, M. ramsayi has 12 closely spaced ossicles which form the strange bumpy projections along the clavus and which are larger than the spaces between them, whereas M. mola only has 8, broadly spaced ossicles. If counting ossicles isn’t your thing, another handy feature to look out for is the reduced band of denticles in front of the clavus that only appear on M. mola.
The above figure shows four images of a Mola ramsayi specimen that stranded in Oman where A) shows its lack of denticle band and B) shows the ossicles on the clavus with more details shown near the fins in C) and D). These images illustrate an awesome paper, documenting the first record of Mola ramsayi from the Sea of Oman, see full reference: Sea NO, Bejgan N (2014) The first record of southern ocean sunfish, Mola ramsayi from Northern Oman Sea, Iran. Iran J Fish Sci 13:242–246.
For a whole body comparison between the two species, maybe the following image is more useful:
The above figure shows (A) M. ramsayi with a scale bar representing 50 cm; so the entire fish was 144 cm in length (photograph credit: Alex Hearn); (B) M. mola from California waters, where the arrow points to the band of reduced denticles (photograph credit: Mike Johnson). This figure is part of a great paper recording the first southern ocean sunfish sighting in the Galápagos, full reference: Thys TM, Whitney J, Hearn A, Weng KC, Peñaherrera C, Jawad L, Alfaro-Shigueto J, Mangel J., Karl SA (2013) First record of the southern ocean sunfish, Mola ramsayi, in the Galápagos Marine Reserve. Mar Biodivers Rec 6:e70.
These two papers provide a wonderful insight into the ecology of M. ramsayi, and I would highly recommend them for further reading on this stunning species. It is incredible how little we know about this fish considering they occur over such a broad area and reach lengths of up to 3.3 m! In 2014, a specimen was caught by a trawler at 85 m deep in Oman, revealing an initial idea of their ranging capabilities… in 2015 we published a sighting at 483 m from an Australian oil rig camera system… and this year a new sighting at 1,112 m deep has emerged from the Galápagos Marine Reserve which represents the deepest dive yet for any species within the Molidae family!!
As always with sunfish research, there is so much more to learn! Since M. ramsayi are not yet assessed by the IUCN (owing to a lack of data), there is a pressing need to further understand their ecology to ensure that sustainable fisheries management strategies are put in place to protect this wonderful species for the future.
If you would like to ask any questions about sunfishy science, academic life or if you spot a sunfish (esp. a stranded specimen) please get in touch using the comments section below or via Twitter: @SunfishResearch or email: firstname.lastname@example.org 🙂