Dive Dry with Dr. Bill

#609: Ranzania from Tasmania? Or Tanzania?

This fall I've been focusing on some of the unusual marine critters that have entered our local waters due to the warm water event and the hurricane events off Baja California the past summer. Time for yet another in this series. I had seen reports on Facebook from SoCal waters of a strange-looking fish that I readily identified from posted pictures as the slender mola (Ranzania laevis) but I hadn't seen one myself yet.

Last week I received a call from Jason Manix saying he had found a strange looking fish near the Tuna Club. Mark KeppelI also found one in Avalon Bay. I told Jason I'd be down shortly (well, actually, at my full height of 6' 1") to take a look. I waited on the city dock and the Can Do approached with Jason on board holding a fish. It was one of the slender molas. I thanked him and immediately took over 60 still images of it. Then I threw the 10" fish out to a waiting cormorant, but despite being "slender," it was too thick for the bird to get down its gullet.

The slender mola is a relative of the ocean sunfish (Mola mola) but is not frequently seen in our coastal waters. It is an oceanic species usually present well offshore in tropical and occasionally temperate waters around the world down to depths of about 450 ft. They swim in schools, so they must be highly educated. However, one source stated they are solitary... perhaps their observations were of fish expelled from class for throwing spitballs. A third source suggested that adults are solitary while juveniles swam in schools... hmmm, just like humans.

Looking at the slender mola you can quickly see the similarities with its larger relative, the ocean sunfish or Mola mola. Both lack true tails and have a short clavus instead, although the larval stage is said to have a tail or caudal fin. The dorsal and anal fins are located well to the rear of the body. My research indicates that these are surprisingly fast swimmers. I certainly couldn't determine that from the dead specimen sliming up my hands! Its mouth is small and oval-shaped, and looking into it you can see a beak-like structure. This helps reveal its evolutionary position with the puffers and filefish. The eyes are fairly large relative to their size. The fish is silver in color but usually a darker blue above with variously colored faint stripes on the dorsal region and dark stripes emanating from the eyes.

It is believed Ranzania juveniles may feed at night on planktonic crustaceans based on the stomach contents of dissected individuals. The assumption of night feeding was based on the presence of a copepod that remains at deep depths during daylight and migrates closer to the surface at night. Another source stated they will also feed on small fish and even jellyfish like their relative the Mola mola.

It seems not a lot is known the slender mola's natural history, probably due to their largely open ocean existence. Fortunately for the species, its sex life has never been featured in Playfish, Pentreef or any scientific journals that I'm aware of. It is believed the individuals in our part of the globe gather and spawn in the central Pacific. At times their larvae are reported in large numbers in plankton tows.

Strandings of Ranzania in coastal waters are believed to occur when strong winds blow them into regions of cooler water and they cannot adjust to the new temperatures. Off South Africa strong winds have caused them to appear inshore and on beaches, but the cold water from upwellings in that area kill them off. Perhaps the strong winds from our recent hurricanes drove them inshore where the cold California Current may have caused the same problem.

I was intrigued to read that the Polynesians consider it bad luck to catch and kill slender molas. They believe this fish is the King of the Mackerels, and that they lead the mackerel to the Polynesian islands where they are fished by the local population for food. I certainly hope neither Jason nor Mark experience any bad luck from finding them... or me for photographing the already dead specimen! I've walked under enough ladders, seen enough black cats and shattered a few mirrors when I looked at my reflection in them to last a lifetime.

© 2014 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Slender mola and tail region; head and view of the oval mouth.

This document maintained by Dr. Bill Bushing.
Material and images © 2014 Star Thrower Educational Multimedia