Sometimes floating mangrove
leaves are really fish in disguise. Batfish take pretending to be
mangrove leaves to an extreme. This post shows a Round Batfish (Platax orbicularis) that I found on the Cairns waterfront, in North
Queensland, Australia.
A round batfish beside a floating mangrove leaf
During April, the surface
waters of harbour are alive the juvenile fish and mangrove-leaf-like
batfish are suddenly present. They lie on their sides and almost
drift passively with the current, making only slow motion movements to
capture small food items.
The fish's face would often come out of the water when it was feeding
The fish would only be vertical when turning
So great was the fish's faith in its disguise, that I could almost poke a camera in its face.
In the few hundred metres of
the Cairns waterfront, perhaps half a dozen are present. Naturally,
I would prefer to be searching for fish in pristine mangrove
wilderness, but my experience is that the marina is by far the best
place to see fish that mimic mangrove material. Mimics seem to
be more abundant in the outer estuary which has large tidal flows. Mangrove flotsom mimics are difficult to find in the long mangrove creeks where the same water moves back and forth
within the creek instead of being flushed and replaced with new water
on each tide. As the marina is at the mouth of the harbour and the
floating concrete fingers trap floating objects, ideal conditions for
observing mimics are present. Still, it is no coral reef and the
pursuit of mimics needs a long attention span and time to waste.
Many species of juvenile fish are only present for a few weeks of the
year as they grow quickly and move to new habitats
Batfish begin life in the
mangroves but live on coral reefs when they are mature. Where they
come from before they become 'mangrove leaves' is not clear. I think
that they first appear as the small dark fish that lurk in the
shadows under the floating fingers of the marina. The dark young
batfish swim vertically and are hard to photograph from above.
Perhaps they mimic dark mangrove detritus, which sometimes swirls
around in eddies below the surface. Fins turning orange is the main
clue that these are juvenile batfish.
In Cairns Harbour, there are
two species of batfish that pretend to be mangrove leaves, the Longfin Batfish (Platax tiera) and the Round Batfish (Platax orbicularis). There are also a several other fish that pretend to be bits of floating vegetation including sea grass, green leaves or
pieces of bark. Perhaps, there are about 20 vegetation mimicking fish
species in total.
Long-finned bat fish swimming around floating concrete fingers
Below are some (suitably licensed) photos from
the net that show how the batfish change after they leave the
mangrove environment. Sometimes the adults return to the mangroves
and can be seen swimming around the mangroves by snorkelers.
