The Skeptical Aquarist

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.... 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