The genus has been redefined three times, and one of our sources is still using a name retired in 1991
Danios are a real genus, which puts them ahead of most shop labels on this site. The problem is that the genus has been split, recombined and emptied out again, and a care sheet written at any point in that history reads as current.
Wikipedia gives the sequence. In 1916, with many more species described in the meantime, the genus was split; the larger species into Danio and the smaller species into the genus Brachydanio. Then: in 1991, though, the two genera were recombined; most larger species formerly within the genus Danio have now been reclassified into the genus Devario. It lists 33 recognized species and gives Brachydanio and Celestichthys among the synonyms.
Aquarium Co-Op writes the zebra danio as Brachydanio rerio, which is the genus that recombination retired thirty five years ago. It is not a competing opinion, it is a page that has not been revised, and this site has met the pattern before: our marimo moss ball record has a source still offering Cladophora, the genus a 2002 DNA study moved that organism out of.
The synonym list settles an argument on one of our own records. Wikipedia gives Celestichthys as a synonym of Danio, and our celestial pearl danio record chose Danio margaritatus against Seriously Fish’s Celestichthys margaritatus. This is the reference source agreeing with that choice, and it is the only danio record we hold.
What the genus does share is a look and a diet. Wikipedia: danios are generally characterised by a pattern of horizontal stripes, rows of spots or vertical bars, some with two pairs of long barbels, and they consume various small aquatic insects, crustaceans and worms. They are found in South and Southeast Asia, commonly kept in aquaria.
What this guide is
- The question
- Three thousand searches a month for a genus of 33 species whose boundaries moved in 1916, 1991 and again as species left for Devario.
- Why it is filed here
- Under stocking, like our rasboras and tetra fish guides, because the school size and the tank are the questions that actually differ between species.
- The record behind it
- Our celestial pearl danio record, the only danio written here and the smallest fish on the list below.
The nine sold as danios, and eight of them are given the same tank
Aquarium Store Depot is the only source we hold that publishes a figure for every type it names. This is that list, unaltered.
| Type | Adult size | Tank | Temperature | pH |
|---|---|---|---|---|
| Celestial pearl danio | 1 in | 10 gal | 65 to 80 °F | 6.5 to 7.5 |
| Glowlight danio | 1.5 in | 10 gal | 64 to 75 °F | 6.5 to 7.5 |
| Gold ring Burmese danio | 2 in | 10 gal | 64 to 75 °F | 6.5 to 7.5 |
| Pearl danio | 2 in | 10 gal | 73 to 77 °F | 6.5 to 7.5 |
| GloFish danio | 2.5 in | 10 gal | 64 to 75 °F | 6.5 to 7.5 |
| Zebra danio | 3 in | 10 gal | 64 to 75 °F | 6.5 to 7.5 |
| Gold longfin danio | 3 in | 10 gal | 64 to 75 °F | 6.5 to 7.5 |
| Leopard danio | 3 in | 10 gal | 64 to 75 °F | 6.5 to 7.5 |
| Giant danio | 4 in | 30 gal | 64 to 75 °F | 6.5 to 7.5 |
Read the tank column and eight of nine are given ten gallons for fish ranging from one inch to three. That is the same figure for a fish and for another fish three times its length, and it is the clearest sign that the number is a category default rather than a measurement. Only the giant danio, at four inches, moves the tank, and it triples it.
The temperature column has two exceptions and one of them argues with a page on the same site. Store Depot gives the celestial pearl danio 65 to 80 °F here, and its own dedicated page for that species gives 72 to 76 °F, which is the figure our celestial pearl danio record cites. Fifteen degrees against four, from one publisher, about one fish. The other exception is the pearl danio at 73 to 77, and Store Depot explains it: pearl danios need a slightly higher water temperatures than other types of danios that can tolerate cold climates.
The size column has an outlier too, and it is the fish that should be hardest to get wrong. Store Depot gives the zebra danio 3 inches. Aquarium Co-Op gives about 2 to 2.5 inches, 5 to 6 cm, long, depending on the variety. Wikipedia gives adults reaching 4 to 5 cm, 1.6 to 2.0 in. The reference figure and the shop figure differ by fifty percent on the single most studied fish in the aquarium trade, which station 03 is about.
What every source agrees on is the school. Store Depot: no matter which species of danio you choose, you will need to keep them in a school, with at least 6 danios kept together at all times. Aquarium Co-Op asks for at least 5 to 6 fish and gives the consequence of fewer: they may fin nip if their school isn’t big enough to keep them entertained. That is the reason this guide is filed under stocking, and it is also the reason Co-Op tells you to avoid slower swimmers, for example betta fish, while recommending rainbowfish, livebearers, barbs, and loaches.
One of them has a sequenced genome, and one of them is a genetically modified animal you can buy
The zebra danio is Danio rerio, and outside the aquarium trade it is one of the standard vertebrates of biological research. Wikipedia: it is extensively used as a vertebrate model organism in scientific research, particularly developmental biology, but also gene function, oncology, teratology, and drug development.
It has been sequenced for a quarter of a century. The Wellcome Trust Sanger Institute started the zebrafish genome sequencing project in 2001, and the genome runs to about 1.4 billion base pairs. No other animal on this site has a published genome behind it, and it is worth holding that next to station 02: the fish whose DNA is public to the base pair is the one a shop page has at three inches against an encyclopedia figure of two.
The research use is also why the wild tolerance figures are so unusually good. Field studies of the water zebrafish actually live in found conditions mostly ranged from 16.5 to 34 °C, 61.7 to 93.2 °F, in temperature with near-neutral to somewhat basic pH. That is a thirty one degree range, wider than any band any record on this site publishes, and it is measured in rivers rather than recommended for tanks.
Then there is the row in station 02 that is not a species at all. GloFish danio is a transgenic animal. Wikipedia: in late 2003, transgenic zebrafish that express green, red, and yellow fluorescent proteins became commercially available in the United States. The fluorescent strains are trade-named GloFish.
Store Depot lists it beside the wild-type danios with the same ten gallon tank and the same 64 to 75 °F, which is correct: it is a zebra danio with an inserted fluorescent protein gene, so the care does not change. What it adds is one instruction, and the reason for it is the trade rather than the fish: it is important to purchase only GloFish in order to avoid alternatives that have been cruelly dyed. A genetically modified fish is here the humane option, because the thing it competes with is a dyed one.
This site has met the same distinction once before from the other direction. Our koi betta fish guide explains a color pattern produced by a transposon moving inside the fish’s own genome, and our alien betta guide one produced by crossing species. The GloFish is the third mechanism: a gene put in from outside, and it is the only one of the three whose result is stable and predictable.
Most of them need no heater, which puts this genus on a very short list here
Aquarium Co-Op says it without hedging for the zebra danio: the fish is comfortable at temperatures of 65 to 75 °F, 18 to 24 °C, and the tank can be unheated at that range. Store Depot agrees and then qualifies: danios do not necessarily need a heater, but a heater is always recommended for any tank setup to keep the temperature stable.
That is the same distinction our betta fish water temp guide turns on, and it lands the opposite way round. On a betta every source asks for a heater and they argue about the setting; on a danio no source requires one and the argument is whether stability is worth the equipment anyway. Both answers are about the swing rather than the level.
Eight of the nine types in station 02 are given 64 to 75 °F, which is below the 75 to 76 the rest of this site shares. A danio tank is a cool tank by the standards of this site, and that is the practical consequence of the genus rather than a preference of one species.
On this site the unheated question has now come up on five pages, and it is worth listing because it is a short list. Our celestial pearl danio record carries two sources arguing the tank should ideally be unheated. Our least killifish record has a source noting it tolerates unheated tanks. Our clown killifish record raises keeping one without a heater. Our axolotl record wants 61 to 64 °F, which most rooms supply. And now the genus that contains the first of those.
Store Depot notes one exception inside the genus and one caution about the celestial pearl danio that our own record should be read against. The exception is the pearl danio, which need a slightly higher water temperatures than other types of danios that can tolerate cold climates. The caution is blunter: celestial pearl danios are not very hardy fish and succumb to imperfect or irregular water conditions, and do better in cooler water temperatures.
That last line is the one worth carrying, because it changes the shape of the advice. A cool tank and a stable tank are not the same tank, and the fish in this genus that most wants the cool water is also the one a source calls least tolerant of irregularity. An unheated room is cool and irregular at once, which is the case for the heater Store Depot recommends and does not require.
Stripes, food and temperament, and the one word every source uses that this genus does not quite earn
Wikipedia describes the whole genus in one sentence, and it is a description of markings rather than of shape: danios are generally characterised by a pattern of horizontal stripes, rows of spots or vertical bars. Some species have two pairs of long barbels. Those three patterns are the three the nine types in station 02 are named for, which is why so many of the trade names are colors and patterns rather than places.
The zebra danio has the horizontal stripes the name records, and Aquarium Co-Op notes that the leopard variety, which swaps stripes for spots, look like a completely different species while being the same Brachydanio rerio with genetic variation. So one of the three patterns Wikipedia uses to define the genus turns out to vary inside a single species, which is a fair summary of why the labels in station 02 are unreliable.
On diet the genus is easy and the sources agree. Wikipedia: danios consume various small aquatic insects, crustaceans and worms. Aquarium Co-Op lists the aquarium version for zebra and leopard danios: fish flakes, nano pellets, freeze-dried foods, frozen bloodworms and live brine shrimp, and recommends variety to avoid nutritional gaps. Nothing in this genus refuses dried food, which separates it from our celestial pearl danio record, where Seriously Fish says the fish should not be fed dried products exclusively, and from our pea puffer record, which refuses flake entirely.
Temperament is where the word every source reaches for does not quite fit. Danios are described as peaceful, and in the sense of not being predators that is true: nothing in the genus is published as a fish that eats its tank mates. But Aquarium Co-Op attaches a condition to the word, and it is the same condition twice: they may fin nip if their school isn’t big enough to keep them entertained, and they should not be housed with slower swimmers, for example betta fish.
That is a peaceful fish with a behavior problem rather than an aggressive one, and the distinction matters because the fix is stocking rather than separation. Six danios do not nip; three do. Our betta record is the pairing Co-Op names, and it fails on speed rather than on water: a long-finned slow fish beside a fast schooling fish with nothing to chase is a bad combination in one direction only.
What the genus is genuinely easy about is the water. Aquarium Co-Op gives zebra and leopard danios pH of 6 to 8 and soft to hard water, which is close to the widest tolerance any fish on this site is published for, and it is why danios are recommended as beginner fish and used to cycle tanks. Set that against the wild figures in station 03, where field studies found the species living from 61.7 to 93.2 °F, and the reputation looks earned rather than inherited.
One species in the genus does not share it, and this guide has now said so twice because it is the fish we hold the record for. Aquarium Store Depot: celestial pearl danios are not very hardy fish and succumb to imperfect or irregular water conditions. Buying a danio for its reputation and getting that one is the single most likely way to be disappointed by this genus.
Ten gallons or twenty, and the disagreement is about the shape rather than the volume
Aquarium Store Depot gives eight of its nine danios a ten gallon tank. Aquarium Co-Op asks for a 20-gallon long aquarium, or longer, for the zebra and leopard danios that sit in the middle of that list. Twice the volume for the same fish, and the word that explains it is the last one.
A danio is a fast, continuous swimmer, which is what Aquarium Co-Op means when it describes them as energetic little speedsters and when it warns against slower swimmers, for example betta fish. A long tank gives a fish like that a lane; a tall one of the same volume does not. That is why the specification is a 20-gallon long rather than simply twenty gallons, and it is the only place on this site where a source names a tank shape rather than a capacity.
The same reasoning runs through the fin nipping in station 05. Co-Op ties the behavior to boredom rather than to territory: they may fin nip if their school isn’t big enough to keep them entertained. Six fish and a long tank are two answers to one problem, and the ten gallon figure in station 02 supplies neither comfortably.
On breeding, this genus is the easy end of the hobby and the numbers say why. Aquarium Co-Op, on zebra and leopard danios: they can release 100 or more eggs per spawning and reach sexual maturity quickly. A hundred eggs from a fish that matures fast is the reason the species became a laboratory animal in the first place, and it connects station 03 to this one: a model organism has to breed on a schedule.
What no source we hold gives is a breeding account for the other eight types. The celestial pearl danio is the exception and it is on our own record: our celestial pearl danio record carries around 30 eggs on Seriously Fish and 12 to 30 on Modest Fish, with hatching in about 72 hours. Thirty eggs against a hundred is the gap between the smallest danio and the most studied one, and it is the only breeding comparison this genus lets us make.
Two things this guide cannot tell you are worth naming rather than filling. None of our sources specifies plants for a danio tank, which is unusual: most freshwater fish on this site come with a planting instruction, and here the closest any source gets is Aquarium Co-Op asking for length rather than for cover. On this site the plants that would suit the cool, near-neutral, moderately flowing water in station 02 are our java fern, hornwort and java moss records, all three of which publish pH 6.0 to 7.5 and two of which tolerate 59 °F. That is an inference from our own rows rather than a recommendation from a danio source, and the record says so.
The other is disease. No source we hold names a condition specific to this genus, which is consistent with a group of hardy freshwater fish and not the same as a clean bill of health. What our sources do give is the behavioral tell: these are described as active fish, Aquarium Co-Op calling zebra and leopard danios energetic little speedsters, so a danio that stops swimming is reporting something the way a betta with clamped fins is, and it is the first sign worth learning on a fish this constantly in motion.
One naming note belongs here because it is the sort of thing that sends a buyer to the wrong care sheet. Aquarium Store Depot: the pearl danio is also known as the blue danio or turquoise danio, and it is a plain iridescent fish. Three names for one fish, none of which is the celestial pearl danio, which is a different species with a different temperature row and, on the same publisher, two different temperature rows of its own.
Danio fish questions, answered from the sources
How many species of danio are there?
Wikipedia lists 33 recognized species, and the boundaries of the genus have moved three times. In 1916 it was split; the larger species into Danio and the smaller species into the genus Brachydanio. Then in 1991, though, the two genera were recombined; most larger species formerly within the genus Danio have now been reclassified into the genus Devario. Brachydanio and Celestichthys are both listed as synonyms of Danio today.
What types of danio can you buy?
Aquarium Store Depot names nine: celestial pearl danio, zebra danio, gold longfin danio, gold ring Burmese danio, glowlight danio, pearl danio, leopard danio, giant danio and GloFish danio. Sizes run from 1 inch to 4. Eight of the nine are given the same ten gallon tank, which is a category default rather than a measurement; only the giant danio moves it, to 30.
How big do zebra danios get?
Our sources differ by fifty percent on the most studied fish in the trade. Wikipedia gives adults reaching 4 to 5 cm, 1.6 to 2.0 in, with wild fish typically 1.8 to 3.7 cm. Aquarium Co-Op gives about 2 to 2.5 inches, 5 to 6 cm, depending on the variety. Aquarium Store Depot gives 3 inches. Note the direction of the wild figure: captive zebra danios are larger than wild ones, which is the reverse of the pattern on our common pleco record.
Do danios need a heater?
No, and this genus is on a very short list here for that. Aquarium Co-Op says the zebra danio is comfortable at temperatures of 65 to 75 °F and the tank can be unheated. Aquarium Store Depot: danios do not necessarily need a heater, but a heater is always recommended for any tank setup for stability. Eight of its nine types are given 64 to 75 °F, which is below the 75 to 76 the rest of this site shares.
How many danios should be kept together?
At least six, and the reason is fin nipping. Aquarium Store Depot: no matter which species of danio you choose, you will need to keep them in a school, with at least 6 danios kept together at all times. Aquarium Co-Op asks for at least 5 to 6 fish and says why: they may fin nip if their school isn’t big enough to keep them entertained. The school is a behavior management tool, not just a preference.
What can live with danios?
Aquarium Co-Op recommends rainbowfish, livebearers, barbs, and loaches and warns against slower swimmers, for example betta fish. That refusal is about speed rather than aggression: a fast schooling fish with a fin-nipping habit and a slow long-finned fish are a bad pairing in one direction. On this site the livebearers are our guppy, platy and black molly records, and the loaches our kuhli loach and dojo loach records.
Is a GloFish danio a real animal?
Yes, and it is a genetically modified one. Wikipedia: in late 2003, transgenic zebrafish that express green, red, and yellow fluorescent proteins became commercially available in the United States. The fluorescent strains are trade-named GloFish. It is a zebra danio with an inserted gene, so Aquarium Store Depot lists it with the same ten gallon tank and the same temperature. Its one added instruction is about the trade rather than the fish: it is important to purchase only GloFish to avoid alternatives that have been cruelly dyed.
Why is the zebra danio used in science?
Wikipedia: it is extensively used as a vertebrate model organism in scientific research, particularly developmental biology, but also gene function, oncology, teratology, and drug development. The Wellcome Trust Sanger Institute started the zebrafish genome sequencing project in 2001 and the genome runs to about 1.4 billion base pairs. No other animal on this site has a published genome behind it.
What water do danios need?
Cool and near neutral. Aquarium Store Depot gives 64 to 75 °F and pH 6.5 to 7.5 for eight of its nine types. Aquarium Co-Op gives pH of 6 to 8 and soft to hard water. The wild figures for the zebra danio are much wider: field studies found water mostly ranged from 16.5 to 34 °C, 61.7 to 93.2 °F, a thirty one degree range, which is a measurement of rivers rather than a recommendation for tanks.
Is a leopard danio a different species from a zebra danio?
No. Aquarium Co-Op: leopard danios look like a completely different species but are the same Brachydanio rerio with genetic variation, and all varieties share similar care. Note the genus in that quotation: Brachydanio is the name the 1991 recombination retired, and Wikipedia lists it as a synonym of Danio. The same applies to the longfin varieties.
Is a celestial pearl danio a danio?
Yes, and Wikipedia settles it by listing Celestichthys as a synonym of Danio. That matters because Seriously Fish gives the accepted name as Celestichthys margaritatus while Wikipedia and the aquarium sources give Danio margaritatus. Our celestial pearl danio record prints the latter and names the argument, and this is the reference source agreeing with that choice. It is also sold as galaxy rasbora, which is wrong.
Are danios hardy?
Most of them, and one is singled out as not. Aquarium Co-Op describes zebra and leopard danios as energetic and undemanding across pH 6 to 8 and soft to hard water. Aquarium Store Depot is the source that names the exception: celestial pearl danios are not very hardy fish and succumb to imperfect or irregular water conditions and do better in cooler water temperatures. A cool tank and a stable tank are not the same tank, which is the argument for the heater Store Depot recommends without requiring.
What do danios eat?
Anything small, and nothing in the genus refuses dried food. Wikipedia: danios consume various small aquatic insects, crustaceans and worms. Aquarium Co-Op lists the aquarium version for zebra and leopard danios: fish flakes, nano pellets, freeze-dried foods, frozen bloodworms and live brine shrimp, with variety recommended to avoid nutritional gaps. That is easier than our celestial pearl danio record, where the reference source says dried food should not be the whole diet.
What do danios look like?
Wikipedia defines the genus by its markings rather than its shape: danios are generally characterised by a pattern of horizontal stripes, rows of spots or vertical bars, and some species have two pairs of long barbels. Those three patterns are what most of the trade names in station 02 describe. One of the three varies inside a single species: Aquarium Co-Op notes the leopard danio, which has spots rather than stripes, is the same fish as the zebra danio.
Are danios peaceful?
Peaceful with a condition attached, and the condition is the school. Nothing in the genus is published as a fish that eats its tank mates, but Aquarium Co-Op says they may fin nip if their school isn’t big enough to keep them entertained and to avoid slower swimmers, for example betta fish. That is a behavior problem rather than aggression, and the fix is stocking: six danios do not nip, three do.
How many eggs do danios lay?
Aquarium Co-Op, on zebra and leopard danios: they can release 100 or more eggs per spawning and reach sexual maturity quickly. It is an egg scatterer rather than a nest builder, which is why the group is easy to breed and hard to breed selectively. No source we hold publishes an egg count for the other eight types.
Which danio is the smallest?
The celestial pearl danio at 1 inch, on Aquarium Store Depot’s own list, and it is the only danio written on this site. Our celestial pearl danio record publishes 0.8 to 1.5 inches from five sources. The glowlight danio is next at 1.5 inches, which Store Depot describes as roughly two thirds the size of a zebra danio.
Which danio is the biggest?
The giant danio at 4 inches, and it is the only one of the nine that changes the tank: Aquarium Store Depot gives it 30 gallons where the other eight get 10. That is a threefold jump in volume for a fish a third longer than a zebra danio, which is a better sign that the ten gallon figure is a default than anything else on the list.