Arius graeffei
Kner & Steindachner, 1867
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he genus Arius is wide ranging throughout the continents
of Asia, Africa, Australasia, South and Central America and there
are about 80 species with the vast amount of them occurring along
sea coastlines, estuaries and coastal lagoons hence one of the common
name of this genus, ‘Sea Catfishes’.
The species we are concentrating on this month is one of only
5 represented in the freshwater rivers of Australia and Papua
New Guinea, the 'Lesser Salmon Catfish', Arius graeffei.
Make sure that you don't let the p.H. drop too low as they like
it more on the alkaline side. They have appeared periodically
in the tanks of retailers and I would be interested if someone
out there is still keeping this species.One cause for concern
is the poisonous spines of the dorsal and pectoral fins as they
will need to be treated with respect as it can take quite a while
for a wound of this nature to heal up if you are unlucky enough
to be punctured.
Colouration is not terrifiic in this species as they have a dark
brown to blue upper body fading to a white/creamy underbelly.
They are also treated as a food fish in its native habitats, they
are renowned for their good taste if prepared properly but some
fisherman treat them as pests as they can get caught in their
nets and can take a considerable amount of time to disentangle
them, and of course as well as avoiding the sharp spines they
can ruin a net for future use.
One very interesting subject that was thrown up by my enquires
was the ‘homeing device’ or electrical fields
that this species possesses and below I have reproduced a published
paper from the Australian Defence Science site from Alan Theobald
DSTO Defence and Darryl Whitehead of the University of Queensland
Australia called, Using Fish Sense for Mine sensing.
“The superior sensory capabilities of fish may one day
replace conventional sonar as a means of detecting marine threats
such as sea mines. New research sponsored by DSTO's Maritime Operations
Division at the University of Queensland's Zoology Department
is exploring the electro-reception used by various fish species
for possible military applications.
For example, catfish (Siluriformes) and sharks and rays (elasmobranches)
can detect electrical fields as weak as 0.07 and 0.001 microvolts
per centimetre, respectively. Researchers at the University of
Queensland have shown that the Australian salmon-tailed catfish
(Arius graeffei) has a sensitivity equal to or better than
any other bony fish. In fact many indigenous animals, such as
platypus and echidna, can detect the very low electric fields
from their prey.
The new research program will target species that inhabit estuarine
waters and, indeed, migrate between fresh and salt water which
have vastly different electrical conductivities. It is hoped that
a good understanding of the physical and biological processes
will result from observing different populations of the same species.
Diagram of
electroreception of its prey by a catfish (Arius graeffei).
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“The illustration (above), for example, shows the changes
in heart rate (top) and blood pressure (bottom) when a voltage
of 70 nanovolts is introduced along the sides of the fish.”
“This research has a long way to go before military applications
can be realised. However, if it is possible to replicate the type
of natural mechanism plus the signal processing chain, then an
alternative to sonar could be produced. In the first instance,
noting that the ranges at which fish themselves detect electric
fields is of the order of metres, this work is targeted at the
possibility of detecting mines, which might be buried in the sea
bed and therefore difficult to detect using acoustics.”
“The basic electro-receptive unit in fishes is the ampullary
organ (shown) which is the ampulla enlarged portion of the canal
containing receptor cells and supportive cells. Receptor cells
are electro-receptive sensory cells and the cup-like cells that
encase them are the supportive cells.”
 “The
length and structure of the ampullary canals varies greatly between
species and habitats. They can be six centimetres long on the
marine catfish (Plotosus anguillaris), whilst on freshwater
catfish they can be just 0.1 to 0.2 millimetres long. The ampullae
themselves may contain hundreds of sensory cells and species may
have thousands of ampullae over the skin.”
“In nature only the toothed whales, such as dolphins and
porpoises, have been shown to have evolved active sonar as a detection
mechanism in water.
Left : Darryl Whitehead, University of Queensland with
Arius graeffei.
Many fish species do, however, detect water-borne acoustic energy
up to a few kilohertz from sources other than themselves.”
“Typically marine animals have evolved other sensory systems
such as olfactory, magnetic, electric and tactile, as well as optical.
These systems are used for both detection of prey and navigation.
By contrast, human technology has developed sonar systems, either
passive or active, primarily to detect underwater objects. Since
World War Two, vast military funding has been directed at the development
of complex sonar systems. This research represents one step in the
search for complementary approaches to sonar for underwater detection.”
Acknowledgments: Darrryl Whitehead of the University
of Queensland for his permission to use his paper, Using Fish
Sense for Mine sensing.
Dorsal 1/7; Anal 15-19; Pectorals; 1/10 to 1/11; gill rakers on
first arch 17 to 22; raker like processes on back of all gill arches,
12 to 20 on first, 15 to 23 on second, 15 to 21 on third; palatel
teeth villiform, in transverse series of 4 oval patches, inner (vomerine)
patches smaller than outer (palatine) patches, patches may fuse
in larger specimens to form two patches or one large patch across
palate; maxillary barbels moderately long, 2.5 to 5.8 in SL, extending
to edge of opercle, usually to above pectoral fin base or midway
along pectoral fin length or below dorsal fin spine in juveniles;
head ovate, snout rounded or slightly truncate; head 3.0 to 3.8
in SL; eye oval, 3.7 to 8.4 (mean 6.1) in HL.
Dark brown, dark blue, fawn or ocher above, sometimes iridescent,
fading to yellowish, cream or white ventrally; some fish from western
Northern Territory with black and cream blotches; fins tan or bluish
brown.
Only A. graeffei and Arius berneyi out of the 5 species
are deemed appropriate for housing in an aquarium as the rest get
way too big for captivity. You would need a good sized tank of course
as A. graeffei can grow to around 18" and if kept with
other fish would need to be housed with larger Cichlids for instance,
as they can be carnivorous, but as far as my enquiry's have thrown
up they can be a good addition to a larger tank.
This fish and some others of its genus have an unusual breeding
pattern for a catfish, it is a mouthbrooder!. The male incubates
the eggs buccally for 2-4 weeks at at a temperature of 32c. When
hatched the young are relatively large and at 2 months of age they
are about 6cm long. The females ventral fins are modified into “claspers”
to assist in the retaining of the eggs as they are extruded. The
breeding season in the wild is reported to be the beginning of the
wet season ( spring or early summer).
In its native habitat they feed on insect larvae, aquatic plants,
prawns, crayfish, molluscs and small fish. In the aquarium they
will eat anything given such as earthworms, chopped liver, frozen
brine shrimp, prawns, pellets, tablets and large flake.
| Etymology |
Arius:
Derived from the Greek word Apelos (pronounced Araios)
which means "sanctified by the god of war", and
refers to the bony structure extending from the skull covering
to the powerful thorn of the first dorsal fin ray.
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| References |
Baench, Aquarium Atlas 3
Allen, R.Gerald.
Freshwater Fishes of Australia.1989.
Burgess, E.Warren
Dr. Atlas of Freshwater & Marine Catfishes 1989.
Top picture: 
Middle diagram & Bottom picture: Australian
Defence Science |
Australia,
from the Houtman Abrolhos Islands, Western Australia to Hunter
River, New South Wales.
Papua
New Guinea, in the Purari River.
