Puddle pirating in the NT – The mangroves

Mangroves are fascinating environments. Usually murky in the Darwin region, the water clarity and salinity can change rapidly with tide and rainfall. The fish that live in it are remarkable.

Mangrove cardinalfish (Apogon hylasoma)

Above is the Mangrove cardinalfish (Apogon hylasoma). Known sometimes as a “gobbleguts” this fish simply inhales other fish. When breeding time comes around, males hold the eggs in their mouth for protection until the young can swim away.

Estuarine toadfish (Batrachomeus trispinosis)

Estuarine toadfish (Batrachomeus trispinosis)

A grumpy looking fish is the Mangrove toadfish. This species is often mistaken for the distantly related Stonefish. They can vibrate their swim bladder to make a humming or croaking sound, reminiscent of a toad or frog. They ambush fish and shrimps using their camouflage.

Sunset or barred gudgeon (Bostrychus zonatus)

Sunset or barred gudgeon (Bostrychus zonatus)

Entering the freshwater drains during the wet season, the Sunset or Barred Gudgeon is an aggressive predator. Even aggressive to their own kind it is difficult to keep more than one in an aquarium.

Lipstick goby (Eugnathogobius nemus)

Lipstick goby (Eugnathogobius nemus)

The Lipstick goby is a comical creature found in shallow sandy pools. Males have red pigment on their lips!

Eurythmus sp

Eurythmus sp

This unidentified eel tailed catfish came from the Finniss river estuary.

Silverbiddy (Gerres sp)

Silverbiddy (Gerres sp)

Siver biddies are cool, they cruise along above the bottom, then plunge their faces into the sand or mud to extract any tasty items buried within. They live in mangrove areas, entering the freshwater after rains.

Hemigobius hoveni

Hemigobius hoveni

This Hemigobius is common around Darwin.

Greenback mullet (Liza subviridis)

Greenback mullet (Liza subviridis)

Mullet are abundant in mangroves, the Greenback mullet is probably the most commonly seen.

Mangrove Jack (Lutjanus argentimaculatus)

Mangrove Jack (Lutjanus argentimaculatus)

Mangrove Jack (Lutjanus argentimaculatus)

Mangrove Jack (Lutjanus argentimaculatus)

Mangrove Jacks are true snappers found all over the tropical Indo-Pacific. Adults live offshore on deep reefs but the young are common in clean freshwater rivers and creeks.

Tarpon (Megalops cyprinoides)

Tarpon (Megalops cyprinoides)

The Indo Pacific tarpon does not grow anywhere near the size of its Atlantic cousin. It is an air-breather and can be found in almost any freshwater or marine habitat, even the most degraded and polluted.

Wilson's mangrove goby (Mugilogobius wilsoni)

Wilson’s mangrove goby (Mugilogobius wilsoni)

Named after a friend of mine, Dave Wilson – the Wilson’s mangrove goby is common in the shallow mangrove pools around Darwin.

Sinuous gudgeon (Odonteleotris macrodon)

Sinuous gudgeon (Odonteleotris macrodon)

During the wet season, the Sinuous gudgeon invades freshwater drains to feed on drowned earthworms. They are a large gudgeon or sleeper, commonly exceeding 40cm.

Juvenile spotted scat (Scatophagus argus)

Juvenile spotted scat (Scatophagus argus)

Juvenile spotted scat (Scatophagus argus)

Juvenile spotted scat (Scatophagus argus)

Spotted scat school (Scatophagus argus)

Spotted scat school (Scatophagus argus)

The above three images show the Spotted Scat, a fish that is at home in either salt or coastal freshwater, feeding on algae and muck, including the poo of other fish (Hence the Latin name)…

Striped scat (Selenotoca multifasciata)

Striped scat (Selenotoca multifasciata)

And there is the Striped Scat also.

Vachell's glassfish (Ambassis vachellii)

Vachell’s glassfish (Ambassis vachellii)

Finally the Vachell’s Glassfish is common in mangroves of Northern Australia, being an important food item for many predators.

Puddle pirating in the NT – Finniss river

Well, you may have noticed the site has been really quiet of late. I have been busy with tourists, Bush Blitz and getting a bunch of fish photos while the dry season here in Darwin hangs on. Not long now and the rains will return and make access impossible to many areas. So let’s have a look at some of the fish I have been encountering in my travels. I’ll start with recent fish from the Finniss region west of Darwin:

Macculloch's [dwarf] rainbow fish from NT (Melanotaenia maccullochi)

The NT dwarf rainbowfish (Melanotaenia maccullochi)

The first is this tiny little rainbowfish – the Macculloch’s or Dwarf rainbowfish. This species is found in patches of northeastern Australia, PNG and one tiny part of the NT, where the local variety is very small and unusually coloured. They sport a pale colour overlaid with black stripes and a red throat. The fin tips are white with a dark submarginal band and a greenish base. This variety is found in extremely shallow water in spring fed swamps.

Primitive, Lorentz's Archerfish (Toxotes [Protoxotes] lorentzi)

The rarely seen Primitive archerfish (Toxotes lorentzi)


Most anglers of northern Australia are familiar with Archerfish- the fish with the awesome ability to weaponize water – shooting a well aimed jet from their mouths at insects, frogs and lizards in the vegetation above. This is the Primitive archerfish, one rarely seen or noticed. Juveniles have tiger stripes and together with adults are found in freshwater lagoons and rivers with lots of overhanging trees. Like the other archerfish species, the Primitive can spit water, though it is not as well adapted as the other species.

Strawman or Blackmast (Craterocephalus stramineus)

Strawman or Blackmast (Craterocephalus stramineus)

Found only in the hard alkaline rivers of the limestone country is this neat little fish. The Blackmast has a tall black and yellow dorsal fin. Feeding mostly on algae and small invertebrates it is a fast swimming species that forms large schools. Delicate and difficult to keep in the aquarium it is spectacular nonetheless.

Giant gudgeon guarding nest (Oxyeleotris selheimi)

Snorkeling in one of the waterfalls I was pleased to find this giant gudgeon guarding a clutch of eggs. This species is often called the “sleepy cod”, a name that belongs to a closely related species (Oxyeleotris lineolata). Ambush predators, they sit and wait for something to swim by, darting out in a flash. This one was about 40cm long.

 

Finniss glassfish (Ambassis sp)

Glassfish are common in many of the northern rivers. This variety is not yet named but it is common in the Finniss. Glassfish are predators, feeding on small aquatic animals.

Into the darkness – A look at the weird fish of Adelaide River

It is true that we know so little about the deep oceans. They’re dark and completely hostile to us, and even with the very best submarines we are still limited with what we can see and do. Closer to land is another mysterious marine environment we know little about, the turbid tidal freshwater rivers of northern Australia and southern New Guinea.

I’ve spent quite a bit of time on these rivers, and it’s amazing the diversity in the muddy, swirling waters. The water is extremely murky, you might normally only get 2cm visibility, at the most maybe 30cm. The water churns as it is forced up and down the rivers by the tide, stirring up sediment and food.

This article looks at the first few critters I found while conducting some casual surveys of the Adelaide River near Darwin, Australia. The fish were all photographed in a black tank as the water is pitch black in the river only a few centimeters down.

An unknown forktailed catfish from Adelaide River in Australia’s NT

In the murky waters it helps to have some sophisticated navigation equipment to find your way around and capture food. This unidentified Ariid catfish probes about with its sensitive barbels. Most catfish also have taste receptors all over their bodies to give them the best chance at finding something to eat. This catfish is extremely flexible and can quickly turn 180 degrees to snap up anything it finds. To communicate, many catfish like this one have the ability to make sounds by vibrating their swim bladder, producing croaks and grunts.

An unidentified freshwater anchovy from the Adelaide River in Australia’s NT

Food is abundant in the dirty waters, much of it is plankton. This Thryssa anchovy lives on the border of fresh and salt water, opening its huge mouth to strain the water for shrimp and fish larvae.

Possibly the first complete, high resolution image of a live nurseryfish. This unusual fish lives in murky estuarine waters of tropical Australia and New Guinea. Males have a hook like protuberance on their heads to hold and guard egg clusters. Almost nothing is known about this fish.

One of the strangest fish of all is this Nurseryfish (Kurtus gulliveri). These fish look and act like they belong in the deep seas. Their eyesight is poor, they are colourless in the wild, translucent and drift about in midwater, snapping up fish and shrimps that blunder too close. The cavernous mouth seems to be able to inhale a large volume of water, likely drawing in prey at the same time. They are weak swimmers, when netted seem to just flop about with no real vigor.

A female nurseryfish

The most remarkable thing about them is the method of raising young. The exact details of spawning are unknown but males end up with a bunch of eggs attached to a hook on their head. Skin grows to close the hook into a simple loop. This is where the eggs remain until they hatch and the young head off by themselves.

A male nurseryfish

A tiny juvenile nurseryfish

There is much more to see in these dark, mysterious waters. I’ll keep you posted on what else turns up…