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Rasboras and Danios.
Rasboras and Danios are Cyprinids that are
so closely related that you'd be hard pressed
to describe the difference between them:
danios generally sport barbels but rasboras
never do. Maurice Kottelat and his co-workers
are beginning to see the genus Rasbora as a kind of catch-all casserole, out of
which they have been pulling separate genera,
like the anagrammatic Boraras micros-- its minute relative B. maculata appears in some of Takashi Amano's aquaria
and turns up on the market sometimes-- and
a couple of Microrasbora species. Even the colorful R. axelrodi now has its own genus, Sundadanio: "danio of the Sunda Isles." These
small schooling fishes fill the same ecological
niches in India and South-East Asia that
Characins fill in South America.
Rasbora (Trigonostigma) heteromorpha. (Harlequin Rasbora). There are about sixty species in the genus
Rasbora but in the LFS, if you just say "Rasbora,"
this is probably the Rasbora you mean. "Heteromorpha," the "different shape," refers
to the body shape, which is higher and deeper
than the classic streamlined rasbora form,
so different in fact that recently (1993)
researcher Maurice Kottelat has proposed
a new genus, Trigonostigma ("trangle blotch") for the three
(now four) "Harlequin" Rasboras.
You may already be aware that R. heteromorpha is one of several lookalike species. A Thai
species, R. espei, which was recognized as a subspecies by
Meinken in 1967 and considered a genuine
species in 1987, even sometimes appears in
the aquarium trade. A smaller "Harlequin,"
maxing out at about an inch, is R. hengeli. It comes from the Tembesi River drainage,
a tributary of the Hari River in central
Sumatra. In 1999 Dr Kottelat and his co-worker
Kai-Erik Witte added still another new Harlequin,
T. somphonsi. Europeans and Japanese aquarists seem to
be adopting the new genus names faster than
Americans.
When R. heteromorpha were first imported into Europe (to Germany,
1906) they had a reputation for being difficult
to spawn. Their homewaters are extremely
soft, with pH dropping below 6.0. Luckily
for us, they have become acclimatized to
harder water over many captive generations,
and they have lost their fussiness. Still,
the more reverse osmosis or de-ionized water
you can use, and the lower the pH drops as
a result, the more viable eggs a spawning
is likely to produce. Broad-leaved plants
seem to be an inducement, for the female
tips upside-down to deposit a couple of eggs
at a time on the underside of a leaf. They
aren't prolific, but left alone in a large
planted aquarium with plenty of hiding places
for the young, R. heteromorpha will maintain their school. Our captive
R. heteromorpha remain smaller than the wild populations.
The common harlequin rasbora R. heteromorpha is found locally quite abundant only in swamp
forest habitats in the Malay peninsula and
Thailand and in the northern half of Sumatra,
typically in warm peaty shaded "blackwaters."
Luckily for the future of the species, it
survives also in more "developed"
and disturbed areas. The collection of this
species in the swamp forest has been described
in the University of Singapore's impenetrable
website http://www.science.nus.edu.sg/%7Ewebdbs/biodiversitii/bio/aquarium_more.html#clownThe specimens are literally scooped out individually
or in groups. Although this is a schooling
species, the dense vegetation and uneven
terrain of the swamp forest makes collection
generally difficult. School children love
to earn pocket money by catching fish in
their spare time. Middlemen pay by lots of
a hundred or per piece. During the low water
season, when the fish population is concentrated
in shallow pools of water, in excess of a
hundred thousand fishes can be obtained within
a week. Shortly afterwards, the populations
often collapse anyway, due to a shortage
of water. So, for this species at least,
University of Singapore biologists anticipate
that the rapid loss of forests (especially
swamp forests) will pose a greater threat
to Rasbora heteromorpha's survival than aquarium-trade collecting
pressure. Though R. heteromorpha are not very prolific breeders, their endurance
in the trade, despite the extensive collecting
efforts, is due in no small part to their
very extensive distribution and the difficulty
in collecting them en masse like other Rasboras.
Even as schooling fish, harlequin rasboras
are not present in huge numbers. That the
species is still extant, even abundant in
some places, means that the current fishing
practices are sustainable.
Czech aquarists Jaroslav Elias and Frantisek
Podvesky's detailed article on R. heteromorpha, reprinted from TFH is archived at www.e-aquaria.com. Linda
Lewis' good introduction to the species,
from Aquarium Fish, Dec. 1991, is archived at http://208.62.34.133/cis-fishnet/afm/G29144.htm
Danio (Brachydanio) rerio. Zebrafish. When I was a kid, no community tank was complete
without a few zebrafish. I took them so much
for granted in those days that I haven't
kept them for years now, I've got to admit.
I hope you can resist the clumsy long-finned
mutants, though,— and the golden forms, where
their snappy stripes are bleached to ghostly
traces. There are about 26 valid species
of Danio in the broader sense including "Brachydanio," which was formerly separated out.
The Brachydanio characteristics, like a shorter anal fin
and a shorter lateral line, are after all
only functions of Brachydanio 's smaller size.
The Danio genus has a wide range, from the upper reaches
of the Mekong River, in southern China, to
the island of Sri Lanka, which has some rare
Danios with very spotty distribution. Recently
Fang Fang, working with Sven Kullander at
the Swedish Museum of Natural History, has
revised the Danios, including six new danios from barely-explored
northern areas of Burma, Thailand and Laos.
If you're interested, look at the brief outline
of Fang's project, with some photos of Danios
you're unlikely to see at the LFS, at http://www.nrm.se/ve/pisces/danipage.shtml.en . The striped danios that even you and I
might identify as quite distinct from the
vertically barred danios are in fact a species
group that is separate from a less familiar
third group of species, which belongs with
Danio dangila, which we never see in the trade. For technical
reasons, since Danio dangila was described first (in 1822), it looks
as though the obscure stranger will keep
the familiar name, while the familiar "danios"
we love are to be cast off in their own genus,
as Devario. Stay tuned.
There are also many casual hybrid populations
of Danio species in the trade: for instance,
it will be rare for you to find the true
Giant Danio (D. aequipinnatus) not blurred with the Queen Danio (D. regina), or to discover the authentic Danio nigrofasciatus, which has been supplanted in the trade
by the hybrid Leopard Danio, a fish that
appeared in 1963. Max Gibbs illustrated some
of these trade hybrids in Aquarium Fish, December 1997, and a version of his article,
"Dashing and delightful" is archived
at http://www.animalnetwork.com/fish/library/
Our familiar long-suffering zebrafish is
becoming the first fish to have its complete
genome mapped. Because the Zebra is used
as a model for studying vertebrate development,
you can find on the web all sorts of arcane
stuff about zebrafish DNA and other cutting-edge
molecular biology that's over my head. But
it never hurts just to have a look, to see
what they're up to. A first look might be
the list of zebra-related biology links at
http://www.golgi.harvard.edu/BioLinks/Zebrafish.html And check out the Zebrafish Information
Network (ZFIN) centered at University of
Oregon. "The Zebrafish Book" at
the site has detailed suggestions for raising
Zebrafish in the labs that might give you
some pointers too: http://zfish.uoregon.edu/index.html And don't miss, under "Publications
and Community," the page "Zebrafish
for K-12!"
Alan Alda hosts a PBS-TV series, "Scientific
American Frontiers." In the segment
"Gene Hunters" he visits Nancy
Hopkins in her M.I.T. lab with 150,000 zebrafish,
to discuss this gene isolating project. You'll
also find a BioScience article on zebrafish genetic research.
A simpler article on spawning Zebrafish is
Reet Thomas's at www.aquariacentral.com
And Mike Edwardes has a notebook entry on breeding Zebrafish,
with his unusually good photos.
Tanichthys albonubes. White Cloud Mountain Minnow. Found before 1932 (when it was scientifically
reported), not by a boy scout as you often
hear, but by scouting leader Tan Kan Fei
(Tanichthys is "Tan's fish"), in cool fast-running
streams on the lower slopes of Pai-yun Shan
(which translates as White Cloud Mountain),
a traditionally revered mountain near Guangzhou
(Canton). The specific name albonubes just re-translates "White Cloud."
Much has happened in Guangdong province since
1932: years of rigorous Japanese occupation
followed by civil war, then population and
industrial pressures. Stanley Weitzman and
Hans-Georg Evers reported in the summer of
1999 that the species was now extinct at
this original location; Randy Carey gives
you a brief note on this grim development
in his Journal, 20 July 1999, at www.characin.com.
This is the fish to recommend if someone
asks you which egglayer they should begin
with. White Clouds are hardy, lively, and
almost as colorful as Neon Tetras. The Germans
used to call the fish the Arbeiterneon, the "Proletarian Neon," back before
World War II, when Neon Tetras were still
exotic imports for rich aquarists only. Dutch
aquarists call them "Chinese Danios."
Different populations have varying color
patterns. The original find have steely-blue
bodies, and red fins with white edges. An
even more southerly race found near Hong
Kong has olive bodies, with red-edged yellow
fins. Longfin variants dubbed "Meteor
Minnows" have been coming and going
in the trade since 1956, but the normally
crisp colors of this species usually become
washed out —and you know how I feel about
mutants. Mike Yamamoto, of Hawaii, wrote
the detailed story of these long-fin variants
in Aquarium Fish, April 1998.
Guangdong is the hilly southernmost province
of China, tropical in climate, but sub-tropical
at higher elevations. White Clouds thrive
best at slightly cooler temperatures, in
the mid-60s, right down to the low 40s without
stress. In an American household, they really
don't need a heater at all.
Breeding. White Clouds breed like Barbs, but they
don't have the same voracious appetite for
their own eggs, if you keep them well fed
with brine shrimp during spawning. More eggs
will survive if there's some loose well-boiled
peat or Java Moss on the tank's bottom. They
aren't finicky about the softness of the
water. I've read about breeding them in "sterile"
tanks free of gravel, furnished with that
green cellophane grass that fills some Easter
baskets. Still, I'd stick to skeins of Java
Moss floating from cork bark chunks; the
protozoans that cover the surfaces of the
moss will provide the best first meals for
the fry. Spawning extends over several days,
so you could replace the Java Moss every
evening and remove it, along with its eggs,
to a fry tank with identical water and a
mature sponge filter. The eggs hatch and
fry appear within 24 hours; better look close:
Mike Yamamoto describes them as "tiny
black splinters."
Links.White Clouds head Mark Owen's page of cool-water
"tropical" fishes at http://www.aquaria.net/art/finart/cool.html
Robin Rhudy devotes a full page to them at
http://userpages.umbc.edu/~rrhudy1/wcmm.htm with full descriptions of breeding and rearing
them and links to further information.
There's a good brief 1997 article written
by Dave Sanford for the Greater Seattle Aquarium
Society magazine, archived at http://www.gsas.org/Articles/1997/white-clouds.html
Ron Finlayson reported to the Boston Aquarium
Society on his success leaving White Clouds
outdoors in summer to breed in a Massacusetts
garden at http://www.bostonaquariumsociety.org/html/daphnian/ron0599.htm
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