Characids and relatives: "Tetras" and Pencilfishes
Characids and their relatives. The name ''tetra'', first coined by aquarists after World War I for a now narrowly circumscribed genus Tetragonopterus, came to be broadly applied to a group of related small and commonly peaceful, generally silvery or semi-transparent South American characids, with splashes of color on body or fins."Tetra" when I was a lad used to embrace even the related pencilfishes and hatchetfishes that I've included in this folder (they're actually members of the larger group Characiformes). When until recently I've continued to talk about "characins", I've simply been using another old-fashioned scientific term to describe tetras; now the authentic "Characins" have been reduced to a group of just twelve genera closely related to Charax, a silvery Amazonian that's seldom imported. The Characinae in the narrowed sense as they're now understood are a sub-unit of the Characids, which rank as a genuine "monophyletic" family, that is, descended from a single ancestor. Because of the huge number of catch-all species in the designation Characidae, and the great variety they present, the compilers of the Check List of the Freshwater Fishes of South and Central America (2003), though they grouped many of the species among well-defined sub-families, left a large remainder, of 88 genera comprising 620 species, as incertae sedis, that is with an uncertain seating within the umbrella grouping. Genetic analysis is beginning to sort out these relationships, but even some of the genera most familiar to aquarists, like Hemigrammus and Hyphessobrycon, are very likely to be disassembled in the near future.
In the Tree of Life Web Project, the Characiform fishes are described, and the relationships among their 14 or 16 families (lumping or splitting still engendering hot debate) are laid out in the type of systematic genealogical chart called a "clade". That the Characiformes inhabit both both the Neotropics and tropical Africa is a reminder that South America and Africa were once joined, in the Cretaceous.
Tetras are shoaling fishes that are happier with at least a half-dozen more of their own species than they would be in a mix-and-match assortment of fishes that seem "similar" to the aquarist. One shoal to a tank is a good general rule.
Spawning characids. Getting tetras to spawn can be a very demanding feat, or it can happen quite unexpectedly. 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 (this was before the era of "fishless cycling"). The aquarium was fitted out with lots of Mopane roots and quite densely planted. Sadly, the adults began to manifest 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 planktonic organism. So I had my H. herbertaxelrodi after all and 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.
Aquararticles has a pageful of links to articles from aquarium society newsletters detailing the spawning of various characoids. There's a laid-back account of classic characin spawning (Flame Tetras, Hyphessobrycon flammeus, in this case), by Oleg Kiselev at The Krib. 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 well-established community tank, I've found.
Veteran aquarist Al Castro offers "Ten steps to breeding tetras", now at the Fish Channel 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: reverse osmosis, distilled or de-ionized water all serve as well as rainwater, he pointed out. Peat moss soaking in a bucket provided 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 used Java Moss as a spawning medium, which also absorbed unwanted wastes, nutrients and toxins, and later provided a grazing ground for the smallest fry. He painted 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 separated the sexes and fed live foods. Goldstein's fish didn't spawn the very next day: "My fish didn't read the books," he said. Instead he left his group of six together four or five days, until 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 was full of detail, but the message is reassuringly simple, thatspawning can be done regularly with little effort."
An article on commercial spawning procedures for Hyphessobrycon serpæ, Brian Cole and Michael Haring's "Spawning and production of the Serpae Tetra," has details that will interest you, though it's slanted towards encouraging the US fishfarming industry. Make a note of the freshwater articles on Tinfoil Barbs, Lemon Tetras or raising Arowana posted at the largely marine aquaculture CTSA site. Most fishkeepers don't know this site.
Characid links.The one outstanding website devoted to the Characids — with some other softwater fishes — was Randy Carey's former site; his old fishroom was one kind of daydreamer's ideal; ranks of 20 gallon long tanks, each typically containing some tetras, some pyrrhulins (the "Splash Tetras") and some Apistos. Fanatic dedication paid off: Randy's characins were breeding in 98% reverse osmosis water, for a start. I miss his website, but don't overlook his article "Spawning and raising Tetras, Barbs and Rasboras" archived at Aquafind, and his current webpage. I think it's the best, most detailed advice ever given for spawning any of these soft-water egg scatterers.
Characidae at Wikipedia.