Thursday, 15 May 2014

Fish with Face like a Frog

In the Old World tropics is a fish that swims with its eyes out of water so that it can see where it is going. This fish is the so-called popeye mullet or shark mullet (Rhinomugil nasutus)

Popeye mullet, Rhinomugil nasutus, close up
A large popeye mullet (Rhinomugil nasutus) feeding in the shallows
The fish are about 25 cm long and swim in the shallowest waters they can find.  In these waters large predatory fish like Barramundi (a large Perch) cannot get close to them.  Obviously, this makes the popeye mullet more exposed to aerial predators like osprey and terns, however the fish have excellent eye sight and if anything moves, they are off!  They leap across the surface back out toward the sea where they can hide in breaking waves and murky water.  Even when lifting my camera up to my eye in slow motion, fish 10 m away would see me and bound away.

Popeye mullet (Rhinomugil nasutus) feeding in a very shallow sheet of water on mud bank
School of popeye mullet (Rhinomugil nasutus) feeding in a film of water on a mud flat
Popeye mullet move in small groups along the foot of the beach and glide over the soft fluid mud with their big white pectoral fines extended.  The ride up onto fresh mud on the first ripples of the incoming tide and happily become stranded when the ripples retreat (picture above).

Minutes before, the fluid mud was the domain of an even more amphibious fish, a species of mudskipper.  The surface of the mud is green with algae and this is probably what the mullet want.  However in my photos the mullet look like they are surface (filter) feeding.  Bottom-feeding mullet stir up clouds of mud so it is easy to tell when they are feeding.

Mudskipper in popeye mullet (Rhinomugil nasutus) habitat
Habitat of  mudskippers at low tide then popeye mullet (Rhinomugil nasutus) on the incoming tide
In Australia, popeye mullet occur sporadically across a range from Rockhampton to Broome but only occur at certain locations within this range.  These photos were taken at Cardwell in North Queensland where popeye mullet are common and occur in small groups.  In the Gulf of Carpentaria, especially Pormpuraaw, the fish occur in large schools that swim along the toe of the beach.  They are not present in Cairns and Barron River Delta despite apparently suitable habit.  

Suitable habitat to my knowledge is very shallow protected coastal waters.  These areas usually have extensive areas of deep soft mud at low tide.  At high tide, popeye mullet swim in the swash of waves breaking on the beach, where the water is both shallow and turbid.  Below is a view of good habitat at the beach in Cardwell, showing breaking ripples over the mud flat at the base of a beach.  

Rhinomugil nasutus habitat - shallow water over mud flats
Popeye mullet (Rhinomugil nasutus) habitat - Cardwell
Try walking along the beach and doing rapid U-turns when a school of popeye mullet are beside you.


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