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Issue: March 2008

Danios Ahoy!

Author: Phil Purser

011 0308
Photographer: Hans-Joachim Richter
Though somewhat underrated in the aquarium hobby, a school of danios can really add some life and beauty to most setups.

“I’ve tried everything to kill those fish, but they just keep on living,” my friend said as he and I gazed into his aquarium. Half-empty, with no filtration, aeration, or circulation, the tank sported nearly opaque walls slick with brown and green algae. I leaned in closer and, cupping my hands over the glass, I could see several silvery flashes darting to and fro within the murk.
   “And exactly why, may I ask”—I began with my hands and face still pressed against the wall of the dying little ecosystem—“would you try to kill your fish?” My friend responded that he simply didn’t want the tank anymore; he was tired of the maintenance and upkeep, but he didn’t have the heart to flush or kill his fish outright.
   Within 15 minutes I was walking out of his apartment with a bag of murky-green water and the tank’s four unwanted inhabitants. The fish that I rescued from their slow death sentence were zebra danios Danio rerio. Exceedingly common (and typically very inexpensive), these fish were purchased by my friend on a whim, and they would have met a slow and grisly fate had I not intervened that day. Named for their light- and dark-striped bodies, the zebra danios are native to Burma, Pakistan, India, and surrounding waterways, and have been mainstays of the U.S. pet trade for decades now.
   But what makes these little fish so popular? It can’t be the low price, as we all know that hobbyists are more than willing to pay well for some of the most vivid and stunning community tropicals available. It can’t be the commercial appeal of captive breeding, as these egg-layers are prolific enough in the wild and on farms and hatcheries in their native lands to prevent American captive breeders from ever breaking even in the same way that the breeders of angelfish, koi cultivars, or discus can. And it certainly can’t be visual aesthetics; for how can such a simple looking fish compete with the kaleidoscope of colors found in the myriad of other tetras, cyprinids, cichlids, etc?

The Ever-Popular Danios
   At the end of the day, I believe the danios are as popular as they are because they satisfy such a wide range of desires: they are inexpensive, active, prolific, and quietly attractive in their own subdued way. Above all, I believe the danios are simply charming animals; their activity in the tank and their peaceful dispositions make them a nearly universally applicable fish. Almost any community tank in existence can be livened up and beautified through the addition of a small school of danios.
   Fortunately, there has never been a better time than right now for purchasing danios. There are currently more species and more cultivars of various species available in the pet trade than at any other time in industry history. And with so many danios in dealers’ tanks just waiting to be purchased, now is the perfect time to get to know a little more about these demure and delightful little fish. So join me as we wrap our minds around the ins and outs of the captive care and natural history of the zebra danio and all its kin.
   Closely related to the barbs, most of these fishes are of the genus Danio, and are native to the swift brooks, rushing streams, and languid backwaters of Thailand, Burma, India, Pakistan, and surrounding areas of Southern Asia. In the wild, these small fish are natural schoolers that find safety in numbers—numbers that may reach up to thousands of individuals, depending on the body of water in question. Larger schools typically form in lakes and ponds, rather than in rivers and flowing streams.
   Danios are diurnal omnivores that frequently take insect larvae, fry, newly deposited fish eggs (including those of their own species), and micro-bits of underwater vegetation. With their upturned mouths these fish most often take their fare from the surface of the water (mosquito larvae are a favorite prey item), but will not hesitate to dine at any level of the water column.
   In turn, these fish are preyed upon by swift-moving predatory species, by aquatic turtles and snakes, and especially by wading birds that spear individuals out of a school with their long, pointed beaks. While all these predators can severely shorten life expectancy in the wild, captive longevity can surpass five to seven years, depending on the species.

Zebra Danios
   Of the commonly available species of danios, the zebra danio is the most widely known. Hailing from India, Bangladesh, and Pakistan, the zebra danio is one of the smaller species. Large adults seldom exceed 2 inches in length. Body coloration in the wild-type zebra danio is silvery white, striped in black to deep metallic bluish longitudinal bars. One of the very first tropical fish to ever be kept in U.S. and European aquariums, the zebra danio is truly a pioneer species of the industry. Its hardiness and versatility have allowed it to be selectively bred, such that a wide variety of unique cultivars whose coloration, pattern, and finnage vary significantly from the wild-type have come into being. Some cultivars include the long-finned variety, whose dorsal, pectoral, and caudal fins are delicate, elongate, and elegant.
   One of my favorite zebra danio cultivars is the leopard-spot variety. This morph, whose black lines have been broken into speckles, wears spots of dark on a silvery-tan base that is reminiscent of the mottled coat of a leopard. A particularly stunning animal is the long-finned leopard variety, which bears the hallmarks of both the spotted leopard pattern and the long, elegant finnage of the long-finned cultivar. Although aesthetically beautiful to say the least, this cultivar is not nearly as hardy or as long-lived as the wild-type zebra danio. Prone to nervousness and poor health (namely bacterial infections when housed in unsuitably cool or filthy water conditions), these animals cannot be expected to fare as long in captivity as their wild-type brethren.
   And of course, there is the always-controversial GloFish™. A transgenic animal bearing a cnidarian gene for red coloration, this fish wears a radiant coat of electric pink to neon red that is unlike anything seen in natural tropical fish. While the original was red, other colors are now available as well. A school of GloFish™ can add an unprecedented splash of color to your tank. When these fish initially appeared, there was considerable speculation about possible horrors that they could cause, but these fears are without scientific foundation. Nevertheless, they are illegal in some places.
   Likely the most easily cultivated egg-laying fish species in the hobby today, the zebra danio is an excellent choice for beginner breeders who wish to learn more about how to cultivate fish in the home aquarium.

Giant Danios
   Second only to the zebra danio in terms of availability and popularity are the giant danios in the genus Devario. Sandy to tan dorsally and ventrally, this species wears stunning silvery to golden splotches and broken lines atop swatches of cobalt blue along their flanks. Taking the common name from the fact that these species may exceed 6½ inches in length and attain a bulk that is easily several times that of a zebra danio, the giant danio is an active schooler that can add both color and activity to the community tank.
   Requiring much larger environs than their zebra kin, the giant danios prefer long, deep aquaria that are outfitted with plenty of tall grasses and leafy plants (either artificial or living will suffice). Because of their large size and endlessly active movements, these fish can easily intimidate other, smaller species such as neon tetras, rasboras, and hatchetfish. Mix with hardy, schooling fish of similar size. Tiger barbs, red tailed sharks, and various catfishes mix well with giant danios, as do other danio species, as well as loaches, small freshwater eels, and other bottom dwellers that will keep out of the swimming range of the danios. Some cichlid keepers use these danios as target fish.
  The variety that is my personal favorite is the black-spotted danio Danio nigrofasciatus. Also known as the spotted danio or the dwarf danio, this species wears a single to double stripe along its flank (like the zebra danio), but also has a single, double, or even a triple line of spots (or broken stripes if you prefer) along its lower flank. Particularly handsome specimens will also bear black speckles in their anal fins. Although they only grow to a demure 2 inches in length, these fish make up for what they lack in beauty with their size. Black-spotted danios also have, as do all their close relatives, a pair of thin, elongate barbels extending forward and downward from the corner of the mouth. Requiring slightly warmer waters than any other species of danio, these fish should be maintained at 80° to 82°F. Coming from some of the swampier environments to host any species of danio, these Burmese fish also fare better in tanks that are heavily outfitted with broad-leafed plants and driftwood snarls. As with all species of danio, house the black-spotted danio in schools of five to twelve (or more) individuals.

Pearl Danios
   If a more vibrantly colored danio is your cup of tea, then I invite you to investigate the pearl danio Danio albolineatus. Growing to an adult maximum of 2¾ inches, these fish come clad in an eye-catching coat of bluish to silvery or mother-of-pearl iridescence that usually only extends over half of the body, with the head and dorsum being golden-tan to coppery. Particularly handsome specimens may have golden striping intersecting this blue hue along the posterior portion of the flank, or they may bear their iridescence over their entire body. Fins may be coppery translucent, or they may bear pinkish to coral-red tinting along their edges. Described by Blyth in 1860, these gorgeous little fish have been a mainstay in U.S. aquariums for almost a century now, and their wide availability shows no sign of decreasing any time soon. The pearl danio’s coloration and beauty is best displayed in a large, well-lit tank containing a populous school of their kind, for the iridescence of these fish shimmers and sparkles in bright light. House in a mature, well-planted tank.

Blue Danios
   Another danio species is the blue danio D. kerri. Although not typically as flush with cobaltine coloration as their pearl danio kindred, the blue danios are an excellent aquarium addition, for they are long lived, nearly as hardy as the zebra danios, and in captivity they readily form very tight schools whose individuals move together with such speed and precision as to give the illusion that the school is a single, uniform entity. It is rare to get this caliber of schooling formation from any other danio species. Wearing a base coat of silvery to coppery scales along the head and dorsum, these fish have a splash of electric blue intermingled with golden speckles and stripes toward the middle and back portions of the flanks. Like the black-spotted danio, this species also bears long, thin barbels extending from its chin. This species has no special requirements in the tropical community aquarium.

Glowlight Danios
   At the opposite end of the color spectrum from the blue-clad danios is the glowlight danio D. choprai, which bears crimson or orange tinting along its posterior flanks, caudal fin, and along the dorsum up through the dorsal fin. Reddish to glowing-orange splashes also occur along the head and through the upper portion of the eye. Golden hues and blue ovals are also common along the flanks; these colors and patterns are particularly handsome when overlaid by a spray of reddish to orange. Hailing from much slower-moving waters than most of the other danio species, the glowlight danio has naturally occurring longer finnage than all other wild danios; its caudal fin, dorsal fin, and anal fin, while not as long or elaborate as the long-finned cultivar of the zebra danio, consist of considerably longer rays and interstitial webbing than any other species.
   Despite its radiant coloration, this species is not to be confused with the GloFish™ danio, for while the two do bear similar coloration, the glowlight danio is a naturally occurring species, and the GloFish™ danio is a genetically altered cultivar of the zebra danio. As you might guess, the glowlight danio is an extremely popular and sought-after species, and as such, it commands a higher price than most other danios. Due to increased exportation from Burma, this species is also becoming more widely available to U.S. and European hobbyists.

Bengal Danios
   A final species to be mentioned here is the Bengal danio. Also known as the Sind danio, this fish has recently been the subject of some debate among taxonomists. Thus, it may be encountered as either Danio devario or Devario devario. Either way, this species is one of the largest of all danios commonly available in the pet trade. The title of “danio heavyweight” frequently changes hands between this fish and the giant danio, for each can exceed 6 inches in length. Although typically a bland specimen, relatively speaking, this fish does sport an attractive mix of coppery hues and bluish to silvery flashes along the lateral surfaces and the caudal peduncle. Unlike most other danios, this species can tolerate surprisingly cold environs, for in nature it hails from the high-altitude and colder-water streams of northern India and Bangladesh. An unheated aquarium that does not drop below 58°F will support these fish, though I personally recommend not housing at temperatures below 62°F. High-end temperatures should not exceed 77°F.

Danios in the Home Aquarium
   Now that we know a little more about each individual species of danio you’re likely to encounter on that Sunday afternoon trip to the pet shop, let’s review a few of the basic care and maintenance conditions that apply to all species and cultivars of danio.

Stocking
   The rule when adding any species of danio to a community tank is to mix them only with peaceful species, meaning species that are peaceful both in terms of nervousness and aggressiveness. Nervous species (such as bala sharks and some other barbs) may be driven into intense stress by the ceaseless movements of a school of danios. The result of such stress could be that your nervy specimens suffer a depressed immune system and fall ill to fungal or bacterial infections, or that they kill themselves outright (anyone familiar with high-tension fish knows how a swift, headlong rush into the glass wall of the tank can be “all she wrote” for the jumpy victim).
   Aggressive species will work the opposite effect within the tank, harassing, stressing, or even outright killing your danios. Avoid mixing with fin-nipping species (or raucous individuals of a normally peaceful species; after all, many fish do exhibit personalities) or highly territorial species such as cichlids. Obviously, utilizing a larger, more elaborately decorated tank over a smaller, more cramped tank will go a long way in alleviating the stressors caused by territorial disputes between tankmates.
   A second major consideration to keep in mind is that danios (all species) are adamant schoolers, and must not be housed in groups consisting of fewer than four or five individuals. If housed communally in large schools of five, seven, twelve, or more specimens, these fish will behave as they would in nature, but if kept too few to a tank, they will retreat back into the plants and wooden structures of your tank and seldom venture out. It is truly a shame to condemn these beautiful and active fish to such a sedentary lifestyle by keeping too few in a tank. Even danios of differing species will often swim and school together when there are enough of them in the tank and they are close in size.

Water Quality
  
Danios, while hardy and long lived, demand high-quality water conditions (don’t let my friend’s cruel treatment of his danios be an example to follow!) and frequent water changes if they are to thrive and display their finest colors and patterns. I recommend maintaining water conditions of stable pH, for when it comes to pH, stability is much more important than any specific pH value. Ideally, 7.0 is best for danios. Keep temps in the high 70s unless you have a species that requires warmer or cooler conditions. Keep ammonia and all other nitrogenous wastes as close to zero ppm as possible by way of biological and mechanical filtration. Water changes of 10 to 20 percent should be conducted weekly to biweekly (at the very least) depending on the size of the tank, the density of its population, and the caliber of your filtration. If kept under unsuitably cool or filthy conditions, these fish will likely succumb to bacterial, fungal, or parasitic infection.

Feeding
   When it comes to feeding your danios, remember that they have upturned mouths, and most naturally feed very high in the water column. Thus, your tank habitat should consist of plenty of open water and your food items should float as long as possible at the top of the water. Flakes of all varieties, floating blocks of tubifex worms, and other floating matter will be greatly relished by your fish. I have also found that sinking pellets can be crushed into fine bits that will float, or at least sink much more slowly than they would in uncrushed form.
   Though they may live just fine their entire lives on mere flakes, danios will readily accept virtually any type of fish food, including tiny brine shrimp and other such minuscule live prey items. As is true of any tropical fish species, danios will benefit from the widest variety of fare that you can offer. Live and frozen/thawed prey items are especially beneficial in helping your danios in maintaining and exhibiting their most subtle and attractive colors.

Conclusion
   The zebra danios that I rescued from my friend’s apartment that summer afternoon quickly adapted to life in my aquarium and went on to live for several more years. With the right understanding of the needs and captive requirements of these active, hardy, and beautiful little minnows, any hobbyist can support a school of danios in their own home or office aquarium. As always, I urge my readers to seek out additional information on any species that they wish to keep. Good luck! D

 

 



See the full article on TFH Digital http://www.tfhdigital.com/tfh/200803/#pg79

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