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THE ROHU SHARK
Text by David Marshall
Our photograph comes courtesy of Mr. Tree, to whom we send
a big THANK YOU, of the Peoples Republic of China who photographed
this beautiful Rohu Shark in the Ruili fish market of Yunnan.
This photograph was first published on the Petfrd web-site
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Natural history
Found in the freshwaters of Asia and Africa are a number of
primarily vegetarian members of the Cyprinidae family (Carps
and Minnows) whose body contours resemble, to various degrees,
those of the marine sharks, thus they have also gained the tag
of 'shark' within their common names.
Although a very rare import for the aquarium fish trade one
of the most spectacular species of 'freshwater shark' must surely
be Labeo rohita, which is probably recognised more easily under
the common names of Rohu and Rohu shark. The people of Assam
would tell us that Rau and Row are the traditional names to
use whereas the people of Burma would say nga-myit-chin in reference
to this fish.
Amazingly these plant eating fish are known to grow to a size
of 200cm, a weight of 45.0kg and reach an age of 10 years. The
temperature tolerance of this specie is remarkable with a range
of between 14 and 30 C. Riverine in nature, they can tolerate
salt levels of 5 ppt.
Youngsters are bright silver in colour with scales that look
as though they were pasted onto the body. In maturity the body
takes on a darker appearance, with mature fish in certain areas
of their natural range showing red edges to the scales, augmented
with black, silver or bright red coloured fins. Youngsters do
look somewhat like sharks but fully grown adults are of a typical
carp shape and their scales seem to fall back into the body.
Compared to the body size that of the dorsal fin is very short.
At all ages the mouth is in a highly placed position.
Natural distribution sees these fish found in Burma, India,
Bangladesh, Nepal, Myanmar and Pakistan. Spawning, which brings
what are normally solitary living fish into groups, coincides
with the southwest monsoons whose savage rains spread flood
water out over grassland. Given a full grown body size and large
ovary weight it is possible for a mature female Rohu shark to
release as many as 2,794,000 eggs at one go.
Commercial use
For thousands of years the Rohu shark has been fished for its
flesh. The first attempts at commercial production revolved
around small fish which were trapped during the monsoon season
and then grown on in the safety of pens constructed within the
rivers themselves.
Since 1957 the Rohu has become the subject of major commercial
and aquaculture production with ponds, small reservoirs and
rice fields forming the main vessels of intense farming. This
has seen importations of aquaculture stock into Cambodia, China,
Japan, the Philippines, Israel, Mauritius, Vietnam, Sri Lanka,
Thailand and areas of the former USSR.. Along with these countries
frozen Rohu flesh is now available in the Middle East, Canada
and, as we shall see, the U.K.
Fish farmers with a cut finger or small open sore etc. never
place their hand(s) into a tank or pond containing a Rohu shark
as medical researchers in India found, during research carried
out in the 1990's, that these fish can carry bacteria responsible
for tuberculosis and although eating the flesh cannot transmit
this disease to the human body contact with this bacteria through
open water is possible.
The Rohu shark attains maturity when 24 to 36 months old. Although
wild females only spawn once in 12 months under hatchery conditions
they are induced to spawn three times within such a period.
To induce spawning the females are given two injections and
male's one injection of a carp pituitary gland extract. The
fish are either spawned naturally, using a ratio of two males
to every female, or have milt and eggs stripped and mixed. The
fertilised eggs take between 18 and 24 hours to hatch.
The tiny fry feed upon zooplankton. When they reach a size
of 25mm this diet is changed to that of unicellular algae and
decaying vegetation. Although supplementary feeds are available
the aquaculture industry has yet to develop an adequate substitute
so decaying vegetation and/or rice remains the main food source
of the nursery produced fish from growing fry to mature adult.
This means that cost effective farming of the Rohu shark is
hard to achieve.
To try and increase body size and the yearly numbers of spawnings
Rohu have been crossed with several types of carp (Rohu x Chinese
carp crosses have been found to live no longer than 12 months)
but none of these crossings have created fruitful production
yields so the race is now on to produce a strong human-engineered
genetic stock of Rohu (something that is also happening with
the beautiful Labeo boga - which beats the Tiger barb for 'fin
nipping') that has all the attributes needed to attain more
successful aquaculture practices.
The most famous recipe that utilises Rohu flesh is known as
Katsuri machchi. For this dish the flesh is mixed with a number
of sweet and sour ingredients that include salt, onion, garlic,
cinnamon and ginger.
In response for a request for information on the Petfrd website
Aquarists' Peter Cottle, Retro gk and Fish Fish Fish all let
me know that they had tasted the flesh of the Rohu shark. Peter
(who has travelled to the Indian sub-continent) had tried this
flesh both curried and grilled. Fish Fish Fish had shared a
flat with a fish biologist from Bangladesh who was able to obtain
Rohu from London's Billingsgate Market and again the flesh was
curried.
In recent years sport fishing for Rohu has become big business
with adventure fishing holidays to Thailand, where these fish
are known as Pla Yissok Tet, the easiest means of coming across
a Rohu in semi-wild habitats. Sweet corn and rice are the preferred
baits. When caught on rod and reel these fish are renowned for
their fighting qualities.
Aquarium care
Here I have to confess that I purchased a Rohu shark, 2.5cm
in length, from an aquarium retail outlet in South Yorkshire
not knowing exactly what I was bringing home and on the strength
that this little beauty had the most brilliantly bright silver
body of any fish I had ever seen.
When research revealed exactly what this 'silver bullet' was
I could have fallen down a mouse hole but decided to persevere
and keep it for as long as space allowed. To start with into
a tank of 60x30x30cm it went and having grown to a size of 15cm
it was placed into an aquarium of 120x30x40cm. Whether these
fish adapt their growth to fit the surroundings or some vital
component was missing from a natural diet I cannot say but my
Rohu ceased growing at a size of approximately 80cm. As my fish
aged the body began to arch but this did not effect its movement
in anyway. The fins did show shades of red but were more often
dark blue.
The Rohu was well settled at a pH of 7 and a constant temperature
of 27 C. It ate vegetable-based flaked food, cichlid pellets
and adored pieces of Thai crabstick. It never attempted to disrupt
the décor and lived in almost perfect harmony, hardly
ever resorting to 'fin nipping', with a group of large Silver
Dollar, a Distichodus affinis, a pair of large Tinfoil barb
and several Synodontis.
When 'spooked' by any of its companions it dived into the gravel
and covered itself in a 'gravel shower'. Like a number of large
cyprinid species it had an almost inbuilt instinct that cats
were bad news and every time the sound or vibration of paws
had been detected on the fish house roof (which my friend Andy
Rushworth believes is a natural defence to similar vibrations
made by fishing birds) the Rohu would be very nervy for several
hours, make sustained 'gravel showers', and I never dare lift
the condensation shield at this time as these fish can jump.
This fish was in my care for close to 10 years when it began
a series of leaps and on the 5th such leap was found dried out
on the fish house floor. I believe that it sensed an end to
life was close and that it deliberately chose to end its days
this way?
From conversations with my friend Andy Rushworth (another regular
Petfrd contributor) and other Aquarists' with an interest in
Asian fish species it appears that I was extremely lucky to
have the chance to keep a Rohu Shark as these fish rarely, and
perhaps wisely, are seldom imported for the U.K. aquarium hobby.
If you can add any further information to our study then please
feel welcome to do so.
Acknowledgements:-
A big THANK YOU to the Petfrd web-site and named members.
References:-
Books
The Freshwater Fishes of India -A Handbook By K.C. Jayaram.
The Fish Fauna of Assam and the Neighbouring North-Eastern
States of India by
T. K. Sen.
Ornamental Aquarium Fish of India by Kishori Lal Tekriwal and
Andrew Arunava Rao.
Living Fishes by Webb, Wallwork and Elgood.
Y.A.A.S. Size Guide for showing fish.
Internet
Fishbase information sheets (see links).
Thailand tourist fishing websites.
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