17 November 2010

Ocean sunfish (Mola mola) in Sturrock Dry Dock

Helen Lockhart
All in a day's work – and a nice day for a swim!

This morning, 17 November, Aquarium curatorial staff responded to a call from someone at the Sturrock Dry Dock, who informed them that a large ocean sunfish (Mola mola) was being left high and dry as the dock was emptying out. 

A team including Two Oceans Aquarium Curator Michael Farquhar, Assistant Curator Claire Taylor, Senior Aquarist Andrea Hindley and Aquarist Kevin Spiby leapt into action and headed off to the dock, which is next to Royal Cape Yacht Club.

Fortunately, when they arrived on the scene they discovered that the sunfish had already been removed from the dock and was lying weak and exhausted in the water next to the quay.

Claire, Andrea and Kevin plunged into the water to orient the sunfish and to harvest parasites from the fish’s body for research purposes. Common to all sunfish, the parasites collected were copepods, also known as fish lice. These are tiny crustaceans and, in this particular instance, resembled miniature horseshoe crabs. 

All fish carry parasites that live either externally (on the skin and in the gills and mouth) or internally (in the gut). When a fish is stressed, the efficiency of its immune system is reduced. It is then less able to protect itself and the parasites flourish.

Collecting samples from the sunfish's skin

Once the parasites were in the bag, so to speak, our team gently righted the fish, pointing it in the direction of the open ocean. Within seconds it swam off, looking strong in spite of its ordeal. We love a happy ending!

Built in 1944, the Sturrock Dry Dock is the largest and oldest dry dock of its kind in the southern hemisphere; it services international and local seagoing vessels.

Sunfish come into the V&A Waterfront, Cape Town and Simon’s Town harbours every summer and are often injured and/or disorientated. They start appearing in October and are often sighted right through to June the following year.

The predominant species in this area is the ocean sunfish (Mola mola). Ocean sunfishes are found in all oceans of the world except the icy polar seas.

Sunfishes are so called because of their habit of drifting at the surface as if basking in the sun. Few people have ever heard of a sunfish, let alone seen one! Those who have seen these enigmatic fish only catch a fleeting glimpse of a fin or a large flat disk before the fish disappears back into the ocean depths. 

Ocean sunfish can grow up to three metres long and can weigh up to 2 000 kilograms. They don’t have tails as other fish do: the caudal (tail) fin has been replaced by a rudder-like structure. Ocean sunfish have rounded, wavy rudders. All sunfish have small mouths and the teeth are fused together in each jaw, forming a parrot-like beak. The beak is internal and hidden from view.

The Aquarium's curatorial team to the rescue

It’s interesting to note that an animal that grows to such a large size feeds on jellies, which have very little nutritional value.

Sunfish are not considered edible as they consist mainly of cartilage and gristle and their flesh is soft and insipid. Also, the skin is extremely rough and similar in texture to sandpaper.

Sunfish are the largest bony fish in the ocean. They’re considered one of the most advanced fish species because of their highly specialised body form. They are also the most fertile of all fish, producing up to 300-million tiny eggs.

Click here to read more about the Aquarium’s conservation and research work with sunfish.

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