Saturday, 6 May 2017

Most Beautiful Fish in the Mangroves

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

Mangrove leaf mimick
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

Platax tiera juveniles

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.

Longfin batfish in transition to adult form

Platax tiera
Mature longfin batfish

No comments:

Post a Comment