The Skeptical Aquarist

When we talk about "Characins" we're using an old-fashioned term to describe tetras and their kin. If we were being consistent, we'd call them "Characids." In the Tree of Life Web Project, the Characiform fishes are described, and the relationships among their 14 or 16 families (still under hot debate) are laid out in the kind of genealogical chart called "cladistics".

Spawning characins. Getting tetras to spawn can be a very demanding feat, or it can be quite unpremeditated. It all depends on which tetra. In 1998 I put eight Black Neons, Hyphessobrycon herbertaxelrodi, in a 33 gallon tall tank to help the initial cycling. The aquarium was fitted out with lots of Mopane roots and quite densely planted. Sadly, the adults developed a bacterial disease that attacked their central nervous system; one after another they succumbed, and I had to net them out. I settled down to let the tank continue cycling properly, but on the 19th day after the doomed tetras had been introduced, I noticed the first of what turned out to be eight fry, lurking under leaves and darting out to attack a copepod or other all-but-microscopic organism. So I was reminded that some tetras can virtually spawn themselves. Penguin Tetras (Thayeria boehlkei), for another example, first spawned for me among Anubias leaves, right in a quarantine tank.

There's a laid-back account of classic characin spawning (Flame Tetras, Hyphessobrycon flammeus, in this case), by Oleg Kiselev at www.thekrib.com. The usual elements are all here: a clean all-glass 10 gal. tank without substrate, but with the bottom covered (with peat and Java Moss) "leaving just about no parts of the bottom accessible to the adult fish," with very soft water with peat filtration resulting in acidic pH, and live food. The newly free-swimming fry get a good nutritional start browsing the biofilm on the Java Moss, and graduate to brine shrimp nauplii. If you'll cover the whole bottom of a tank with Java Moss, some tetra fry will grow to maturity even in a community tank, I've found.

Veteran aquarist Al Castro offered "Ten steps to breeding tetras" at the Aquarium Fish website.

Robert J. Goldstein pared away some myth and mystique about spawning characins in an article "Breeding Neon Tetras" in Aquarium Fish July 2000, pp 36-41. R/o, distilled or de-ionized water all serve as well as rainwater, he pointed out. Peat moss soaking in a bucket provides him the blackwater component, but alder berries, which some German aquarists use to acidify the water, seemed to him to have no effect. He too uses Java Moss as a spawning medium, which also absorbs unwanted wastes, nutrients and toxins, and later will provide a grazing ground for the smallest fry. He paints three sides of his 10-gallon spawning tanks to provide the dim secure environment that encourages spawning, but you could substitute brown wrapping paper. He separates the sexes and feeds live foods. Goldstein's fish didn't spawn the very next day: "My fish didn't read the books," he says. Instead he left his group of six together four or five days, till he spotted the first glass-like fry clinging to the glass. Then he removed his spawners, even though the females still looked swollen. That seems a pretty sensible touch, rather than trying to wait for spawning to be "over." Apparently the bottom of his spawning tank gets loosely littered with peat moss sediment, which may provide some extra cover for eggs and larvae. The article is full of detail, but the message is reassuringly simple, "that it can be done regularly with little effort."

In Hawaii, the Center for Tropical and Sub-Tropical Aquaculture posts an article on commercial spawning procedures for Hyphessobrycon serpæ, titled "Spawning and production of the Serpae Tetra." Though the text is slanted towards encouraging the nascent Hawaiian fishfarming industry, there are details here that will interest you. Make a note of the other articles there, on Tinfoil Barbs or raising Arowana. Most fishkeepers don't know this site.

Characin link. The one outstanding website devoted to the Characins— with some other softwater fishes— is Randy Carey's site, www.characin.com. Randy's fishroom is a daydreamer's ideal; ranks of 20 gallon long tanks, each typically containing some tetras, some pyrrhulins (the "Splash Tetras") and some Apistos. Check the posted list of fishes Randy has successfully bred since 1991. Fanatic dedication pays off: Randy's characins breed in 98% reverse osmosis water, for a start. Don't miss his article "Spawning and raising Tetras, Barbs and Rasboras" at the site. I think it's the best, most detailed advice ever given for spawning any of these soft-water egg scatterers.

Carnegiella strigata (Marbled Hatchetfish). There are two subspecies of this surface-hugging hatchetfish, one from pools and small side streams in the upper Amazon, where Peru, Colombia and Brazil come together, the other from Guyana and Suriname. Every aspect of their structure identifies them as fishes that haunt the surface. In natural surroundings most of their food consists of insects that have fallen on the water and the smallest water-dwelling crustaceans. So, though they're very good about eating flake food, they'll thrive better if you supplement the flakes with some freeze-dried bloodworms or daphnia, or some live fruit flies. They're uneasy kept in solitude. They love some current and will hang out together in the filter outflow. You know what jumpers the hatchetfish are; sometimes they have been called "freshwater flying fish." If you're keeping hatchetfish, drop your water level several inches to give them some headroom, and give them some reassuring floating plant cover, using Water Sprite, for example. With the security of shade, they'll show more subtle tints in their scheme of a silver belly shading to olive-brown back overlaid with dark streaks and marbling.

I generally leave my tanks alone as much as I can, keep my paws out of the water and let them get on with whatever they're doing, but fishes that jump out at the first opportunity, before I even do anything to alarm them... well they make me skitterish too. Nobody around here seems to breed hatchetfish consistently, and in the U.S. we still rely on wild-caught stock, though Singapore supplies European fishkeepers.

Chilodus punctatus (Spotted Headstander). ("kye-LO-dus:" toothy lips) Here's an underestimated fish that's widely distributed in the weedy backwaters of the Amazon basin, in the Tocantins, Rio Negro and the Orinoco, even in Guyana, where it was first collected "from the standing waters of the savanna" in the 1840s. The various populations have some local differences. It's a biofilm grazer like the Nannostomus species, and it needs to be constantly supplied with some vegetable supplement. Chilodus punctatus has sometimes suffered from getting confused with a moderately closely-related headstander, Abramites, which does have a well-founded aggressive reputation. I have found these shy and gentle fish to be subtly competitive among themselves, not unlike Nannostomus. Though the Baensch Atlas (v.I, 318) says that they're found in schools, I notice a change in their behavior within a few days, even with shipments that have arrived in dealers' tanks. Schooling is largely a fright reaction, I think. Perhaps the fin-flaring and body-shimmying that I witness may just presage early jockeying towards some pre-nuptial condition. Surely they're much more interesting if you keep them in a group of three or four, well matched for size.

Chilodus punctatus has been very occasionally bred in aquaria--— Rolf Geisler gave an account in TFH as long ago as Aug. 1959--— but not yet on a commercial scale. Not enough market pressure for them, I imagine. In the U.S. at least, the fishes you buy are likely to be wild-caught. They will probably arrive home starving, but too frightened to eat. Try to avoid purchasing individuals with very flat, knife-thin abdomens. They may be suffering from intestinal nematodes, too, so they bear careful watching in a full-length quarantine that includes pre-emptivede-worming medication.

The fish are at home in a well-planted aquarium, with open space to move around in but some dark shadowed places near at hand, suitable for a moment's refuge, and with the added security of drifting green plants overhead. Soft water filtered with some peat is preferred. Tannins and low pH tend to reduce the bacterial load; these fish are prone to finrot and intestinal problems if they don't have constant greens. In sympathetic surroundings, the silver of their body color will become suffused with rosy golden and olive tones as they mature. A photograph at a Norwegian aquaristic website gives a good impression. Each scale has a warm black botch at its base and is delicately outlined with black to create a subtle all-over reticulated patterning. The bold lateral stripe is inky black. The eye is rosy red. But it's the obliquely vertical stance of these fishes that makes them memorable. It isn't easy to keep Chilodus punctatus in robust condition; they will take flake food and algae wafers, but they need to have some live food to supplement it, and vegetables to supplement their algal pickings. And they won't thrive with boisterous tankmates.

Links. Aside from abbreviated entries in fish species, there's not much. The Aquaworld website has some useful detail.

Hemigrammus bleheri (Rummynose Tetra). Randy Carey has updated his 1993 article, "The Three Species of Rummy-Nose Tetra" at his website, with his additional notes: www.characin.com If you're interested in these tetras with a reputation for being delicate, that's the first place to look.

If you're looking for a consistently schooling tetra, the Rummynoses fill the bill. Conversely, don't keep them in groups of fewer than six.

Hemigrammus erythrozonus (Glowlight Tetra). Erythro does mean "red," but the brilliant eyelight and body bar of a Glowlight Tetra can vary from clear bright red to the pink of highly-polished new-minted pure copper. Otherwise, the fish is a fairly translucent brownish, with a silvery white belly. There's a red leading edge to the base of the dorsal fin. Peat filtration and a dark woody background bring out the touches of icy white at the leading edges and tips of fins. What small mouths they have. The fishes max out at about an inch and three-quarters, with females notably more robust.

These beauties were first noticed in a temporary overflow pool in the floodbottom of the Rio Mazaruni, in Guyana (then British Guiana). H. erythrozonus are also found in the Potaro and the Essequibo rivers; in other words they're well-distributed through the central watersheds of Guyana. They were formally published to science in 1909, but they didn't get exported til 1933. Glowlights for the market are all bred now in Singapore.

Spawning doesn't quite follow standard tetra procedure, in that the male performs an enticing courting dance for the female, blocking her movements to give her shimmying broadside displays. If she's ready to accept him, their excited fin-flicking movements will build to a climactic side-to-side barrel roll in which about a dozen eggs get extruded in a burst. The eggs will be eaten as soon as spawning heat has cooled, so be prepared to remove the pair. A good trick is to provide a removable screen divider, with plenty of Java Moss all on one side, where the slightly tacky eggs will stick. With the divider, you can separate the pair for a day or two beforehand, and then screen them from their eggs caught up in the moss afterwards. Though Glowlights will even spawn in water with a pH slightly above neutral, they have a reputation for not being very forthcoming about spawning. They mature early and spawn only while they're young. In my soft water, flirting pairs form even in a planted community aquarium, so I think the problem of reluctance to spawn may be in the hardness of the water. When I'm told that the extremely tiny eggs will swell once they're out in open water, I'm reminded that the water has a lower molarity than the fluids in the fishes' ovary. So it occurs to me that reports of hard water reducing fertility of spawnings might have some connection to impaired osmotic reaction of the egg membrane when water is not very soft. If your Glowlights are resisting spawning, see whether you might encourage them by doing a part water change with some distilled water.

Within a month of hatching, well-fed fry will start to show iridescence. They look like a cloud of sparks, if you can have them against a dark woody background.

Animal researcher Grant E Brown and his co-workers have been investigating Glowlight Tetras' reaction to the alarm pheromones that tetras exude when they are attacked or harmed. The effects of an unidentified characoid "fright substance" have been recognized for decades, but recently the actual molecule has been tentatively identified. Alarm pheromones are produced by all Ostariophysii, the giant group of fishes that includes catfishes as well as tetras. In a series of experiments starting in the 1990s, the researchers showed that H. erythrozonus even detected the fright substance exuded from predatory Cichlasoma that had recently dined on tetras. Their alarm responses included increased shoaling, more restricted cruising the tank, more hesitancy about inspecting the cichlid. And "fin-flicking:" if you know Glowlights and some other tetras, you'll recognize the action of "fin-flicking," but you probably didn't identify it as an alarm display to alert other Glowlights— nor did you imagine that the twitching gesture had some deterrent effect on potential predators. If fin-flickings are important communicating gestures, that would give a purpose to the leading edges of Glowlight fins being heightened with white. Abstracts of Grant Brown's articles are posted at http://www1.union.edu/~browng/; follow links to "Publications."

Hyphessobrycon herbertaxelrodi (Black Neon). I keep Black Neons in my somewhat generic "Amazon" aquarium, even though they aren't fishes of the Amazon Basin; in fact, Black Neons come from the Mato Grosso, far to the south in Brazil, in the Rio Taquari, which is part of the Paraguay drainage. The area was for long inaccessible even to a cargo plane, so remote that Hyphessobrycon herbertaxelrodi didn't arrive in the U.S.A. until 1960. The clunky name honoring Dr. Axelrod set off a tiresome modern fad for flattering v.i.p.s with attaching their complete names to new species: why not "doctorherbertraxelrodi" while you're at it, eh?

When they were first imported, Black Neons seemed to require soft water and peat filtration, but they have settled down in captivity. Any that you may see are captive bred, and no one thinks of Black Neons as especially delicate and demanding tetras any more. In fact, if they are well-fed, and not too jostled and distracted by other species, Black Neons will spawn casually in a community tank, if water is soft and pH is slightly acidic. Peat filtration will help. You'll see them sporting and chasing in the evening, and in the morning, unless you're up at dawn, it will all be over: the females will be slender once more and the eggs will have all disappeared.

The patterns and the colors or transparency of fishes is never arbitrary. We know that selection by predators and by sexual attraction have shaped these animals. But I was vividly reminded of the survival value of Black Neons' patterning one afternoon when I was watching them dashing back and forth in a shaft of sunlight. The upper body of this fish is all but transparent. The bold irridescent green stripe down the center of the fishes' flank marks a sharp upper edge to a black streak that counter-shades away below to a silvery white belly. I suddenly compared the fish in sunlight to a small shiny horizontal leaf with a blinding band of sunlight across it and its top facing me in shadow. How unfishlike the camouflaged Black Neon appears. Then it turns away to flee and disappears, like a deep-keeled cardboard fish-shaped cutout that's suddenly been turned end-on! What is a predatory fish presented with? —a flash of irridescent green, like a leaf surface caught in sunlight, then a snap disappearance!

Though they tend to shoal together, a slight degree of intra-specific aggression keeps H. herbertaxelrodi from acting in unison as a true school.

Hyphessobrycon (Paracheirodon) innesi (Neon Tetra). In 1936 visitors to the Shedd Aquarium in Chicago lined up to view exotic Neon Tetras for the first time. The fish had been collected in the Amazon and shipped to Germany. Then they were flown back across the Atlantic in the dirigible airship Hindenburg.

Neon Tetras are now many generations removed from the clear and blackwater streams where they were first discovered and exported. Their home territory is the lower Putumayo River and the Leticia-Tabatinga district where the borders of Peru, Colombia and Brazil come together along the upper Amazon. They can be found as far down the Amazon drainage as São Paulo de Olivença. For years, while Neon Tetras were being flown out of Leticia, the exact locality from which they were being collected was kept tightly controlled as a "trade secret;" it was even withheld from the scientists who formally described them. The location wasn't revealed til about 1960.

All but a tiny percentage of Neons on the U.S. market now come from Hong Kong, where cooler weather encourages more prolific breeding than in Malaysia and Singapore. In a brief 1998 bio of Neon Tetras by Dr. William Fink's biology student at U. of Michigan, Emily Couture, (now deleted from the Web), she emphasized how little is known about Neon Tetras in their native habitat, and incidentally remarked on the disease susceptibility of mass-produced Neons that are farmed in continuously medicated water in southeast Asia.

In 1998 Prof. Frank Chapman and some colleagues at the University of Florida wrote an article "Controlled spawning of the neon tetra" in the journal Progressive Fish Culturist, to encourage Florida fish farmers to take up the domestic production of this popular species. Robert J. Goldstein spoke to Prof. Chapman while doing preparation for his article, "Breeding Neon Tetras" for Aquarium Fish July 2000, and Chapman expanded on his published thoughts about why Neons were such meager producers, when aquarists got them to spawn. Chapman thinks that the Asian fish are fed chow laced with testosterone, a common "color enhancer." The testosterone makes the young fishes color up prematurely, so that they're marketable at barely half an inch, whereas unjuiced juveniles don't begin to show their colors til they are a bit larger. Chapman thinks that testosterone is decreasing females' fertility. Of course, once you have raised your own tank-bred Neon Tetras, female fertility will be back to normal in the next generation. So, the next time you're at a club auction event, you might consider paying a premium for a member's tank-raised Neon Tetras.

But good news follows Chapman's work at the University of Florida; much healthier neons from Florida fish farms are beginning to come onto the U.S. retail market. A January 2001 U. of Florida press release announced that the breeding "secrets" were slightly acidic, soft water at 77oF. Hmm. No surprises for you there!

Mike Edwardes gives a useful report on breeding neons at his website.

Nannostomus marginatus (Striped Pencilfish). I don't know why I haven't explored the Nannostomus more. There are some fifteen species of Nannostomus, members of the Lebiasinidae, which makes them close relatives of Characins. All of them have long cylindrical bodies and the "tiny mouths" their name specifies. Adults reach almost 2 inches, and, in a flattering reversal, they grow larger for us in aquaria than they are found in nature. Probably they live longer in aquaria, too, under the right conditions. All the Nannostomus have a reputation for being delicate, when they don't have the clean, soft, acidic waters they require. Variable Nannostomus marginatus populations are found in the mid- to lower Amazon, Rio Negro and Orinoco river systems, in the upper Amazon basin of Peru, and in the Guianas too. There is a separate population of N. trifasciatus with a distinct ocellated spot in the tailfin in the Rio Apeu, near Boa Vista, Para, Brazil. They have been collected in shoreline reaches of the Amazon itself, but they more characteristically range up into small shaded tributary streams, the kind of forest environment that is most under attack from short-term speculative forestry and cattle-ranching. "Most of the species with wide distributions are geographically somewhat variable regarding life color patterns, scale counts and sometimes vertebral counts," wrote characin guru Stanley Weitzman in a Tropical Fish Hobbyist article, May 2001, "Nannostomus marginatus and a related coral red form;" this is the most useful print article on this species and a public introduction to the newly found coral red form.

Perhaps Nannostomus marginatus are the most beautiful Nannostomus. Mine seem to be from the Rio Negro population, a silvery gold with clean black stripes, with small flecks of nail-polish red. The clear parts of the fins reflect a skim-milk bluish sheen in reflected light. Alpha males in competition flush rosy red. At night the fishes take on a different, protective coloration, drab gray with three vertical dark blotches. In an aquarium that combines small open spaces with dense surface tangles they lose their shyness, but they wouldn't thrive with really boisterous tankmates. They always keep that dash-and-freeze behavior that is so characteristic of fry and of many small fishes. The floating tangles in my aquarium are important, for that is where Nannostomus prefer to deposit their spawn, I hear. They hold a station below a leaf or in the pendant roots of Water Sprite, from which they rush out to challenge their conspecifics with fin extensions and broadside shimmying. If that doesn't work, vigorous body-slamming is called for. Though no harm is done, no permanent pecking-order seems to get established either. This behavior has overtones of pre-nuptial jockeying, but I haven't caught mine in the act. Quite often, schooling behavior is reported: in the Baensch Atlas, for example, or in a capsule bio by U. of Michigan Biology student Mara Zimmerman that's unfortunately been deleted at http://www.umich.edu/bio440/ —but I'm convinced this is shoaling, not schooling, a fear reaction that is a temporary artefact of laboratory conditions. The schooling behavior I mean. All that remains of Mara Zimmerman's good brief report, with a bibliography, is the best photo portrait of N. trifasciatus on the web.

Currently I have two rival males and four plump females in a densely-planted 10-gallon tank. One male keeps the females loosely herded in a harem. The other male challenges. The females don't seem to have any strong loyalties. The spawnings are eaten by Melania snails before they hatch. It took me months to figure that out.

Randy Carey also has beautiful close-ups of this photogenic fish, and a well-written brief article, at www.characin.com. My fishes have the red mid-body splotch he takes as a mark of N. marginatus. Stanley Weitzman and Richard Vari say, "Complex distribution patterns, active speciation, and variable chromosome counts make this a challenging genus for taxonomists, and species limits are ill-defined." (in Paxton and Eschmeyer's Encyclopedia of Fishes, 2nd ed., 1998, p102). No doubt some inadvertent further blurring of Nannostomus populations has taken place in the aquarium world.

The T.F.H. article I mentioned was occasioned by the first importation, in late November 2000, by Julio Melgar of Acuario Nanay, of some N. marginatus in which courting males flushed a strong red. The new find comes from small streams in the mid reaches of Rio Nanay, near the village of Albarenga, and from tributaries of Rio Tigre, near Santa Helena, in the province of Loreto, Peru, west of Iquitos, whence these wonderful fishes are being shipped. The males display even to their mirror reflections, and the coral red color fades when they aren't in displaying mood. In courting, the male approaches the female from behind with his anal fin spread wide so as to cup it round the female's vent, concentrating his sperm round the shed egg, which improves chances of fertilization.

Spawning N. harrisoni. Randy Carey describes his set-up in "Randy's Fishroom."

Paracheirodon axelrodi (Cardinal Tetra). The only question is, what's the second most glorious tetra, right?

Their home waters in the upper Orinoco, Rio Vaupes and northern tributaries of Rio Negro aren't the tannic blackwaters of traditional aquarists' lore after all, it appears, but instead shaded clearwaters. Softness counts when you're trying to please Cardinal Tetras, and the pH can drop below 6.0. The limestone waters of Florida will never suit them for breeding: in the U.S.A. these fish are still eluding the mass manufacturers and come in, wild-caught, somewhat seasonally, from the mid-reaches of the Rio Negro. In Europe, however, they are bred for the market. Even at home, if you can't give them the very soft, acidic water they need, they'll never show their most intense color for you. The golden cast of peat filtration, some patches of shade from floating plants and a dark woody background, such as natural corkbark, present Cardinal Tetras at their best. A school is a must, or they'll be disoriented and shy.

These fishes first were first discovered in 1952 by Harold Sioli in a tributary of Rio Negro. In the winter of 1955-56 the first shipment of them was sent to New York, flown out from Manaus by the largest exporter, Paramount, who were pioneers in shipping Amazonian fishes by hydroplane. The new species was about to be formally named Hyphessobrycon cardinalis by Dr. George S. Myers (of Stanford) and Weitzman. But lo! the publication date of a newcomer magazine, Tropical Fish Hobbyist, was advanced by a few days, so that a rival scientific name honoring its publisher gained precedence. The ensuing dispute went all the way to the International Commission on Zoological Nomenclature before it was settled!

In Europe, the market is supplied by breeders in the Czech Republic. Wild stock for the U.S. market are still collected around Barcelos on the mid Rio Negro about 430 km from Manaus, and exported from Manaus, where the Rio Negro joins the Amazon. The fishing season coincides with low water levels from October to February. The Cardinal Tetra is the indicator species for the ornamental fish trade in the middle Rio Negro basin. During the severe El Nino event of the 1990s, drought in the Rio Negro basin dried up populations of Cardinal Tetras in all the accessible creeks and igapes, causing some consternation in eco-circles, but after the rains returned, the natural populations bounced back in two seasons. The general lesson is, few tetras survive to maturity in nature. Cardinal Tetras are virtually annual fish, though they live for five years or so in an aquarium.

Broader concerns, about the sustainability of the ornamental fishing trade that is founded on Cardinal Tetras, (which still represent some 80% of exported Rio Negro fishes), and the social impact of the trade, are being studied by the Projeto Piaba, begun as a biological inquiry in 1989 but working now to develop a responsible sustainable Rio Negro ornamental fishery. You might be interested in reading about the Project and the Rio Negro fishing community at the Projeto Piaba website.

In Cardinal Tetras from the Rio Negro, the iridescent blue-green line ends at the base of the little adipose fin. In Rio Orinoco populations, the stripe ends short of the adipose fin, with a red streak that's noticeably wider in the caudal peduncle.

In the Rio Negro there are also some "blond" or "golden" Cardinals, more curious than desirable, in my opinion.

There are some discussions of Cardinal Tetras in Conservation and Management of Ornamental Fish Resources in the Rio Negro Basin, 2001 (proceedings of an international workshop on Amazon River Biodiversity at St. Louis, 1999). I can't nail down a dependable link, but a google.com search for the key words will find it.

Besides Cardinal Tetras and Neons, a third look-alike tetra is Hyphessobrycon (Paracheirodon) simulans, rarely seen. But if you know what you're looking for, you might pick out a few as "contaminants" in a tank of imported Cardinals or Neons..

Thayeria boehlkei (Penguin Tetra). Thayer, for whom the genus is named, was the underwriter of the Amazon expedition of 1865-66, which had for its geologist-biologist the famous Louis Agassiz. Agassiz was more than an ichthyologist; in his youth he made his public reputation expounding the fresh idea that there had been an "Ice Age," and in time Agassiz lived to become the last widely-respected professional biologist to resist the concept of evolution. The species name is for J.E. Bohlke, an ichthyologist at Philadelphia's Academy of Sciences.

This species is from Rio Araguaia and also from the upper Amazon basin in Peru, but the fish you'll buy have been shipped from Thailand or Singapore.

When this tetra came on the U.S. market it was confused with another, T. sanctæ-mariæ, and the mistaken identity persisted for years. When it's at rest, this fish has an unusual up-slanted posture that's emphasized by the black lower lobe of its caudal fin. Does the slanting black stripe and blot make its outline read as less fishlike to a predator, I wonder? These bold fish are competitive with each other, but in all the mutual chasing I've yet to see a fin torn. If you think of tetras as pure carnivores, like mini-Piranhas, you'll be as surprised as I was to see Penguin Tetras tear into a floating blanched spinach leaf.

This is an easy tetra to spawn. The females regularly fill with eggs. Pre-nuptial broadside displays, and rushing and feinting get more excited over a couple of days till in an evening fishes start to pair up and make wild dashes through the plants, with eggs blown in every direction.