Danios & Devarios
Until recently, the number of Danio species available to the fish keeper could be easily counted on one hand, but in recent years several species have arrived on importers lists, and given their ease of keeping and breeding, there should be no reason for them to disappear. Danios are ideal for adding activity to an aquarium, and are peaceful enough to be kept in a community of small or medium sized fishes.
Danios & Devarios
For the purposes of this article, we will refer to all the species as 'danios', although there are actually two families, danio
. In general, danios have barbels, whilst devarios do not, although there are some exceptions. It can be very difficult to distinguish the differences between some species, so we should be thankful that they all have very similar requirements, since it is not uncommon for species to be imported or sold under an incorrect species or common name. Danio and devario species available in the trade typically reach between 3-12cm, so are a manageable size for aquarium keeping.
Danios are part of the Rasbora family of Cypriniformes, and originate from streams and small rivers in Asia, particularly around Sri Lanka, Malaysia, and India. The most famous of all the danios is the Zebra Danio, which is bred in huge numbers both for the aquarium trade and for genetic research. The fish has importance in genetics since it is a manageable, robust, species and can be bred in successive generations relatively quickly.
Whilst experiments with live animals for genetics research have their importance, the resulting strains should never be released into the public domain for the purposes of making money in the pet trade. This has unfortunately already happened with the Zebra Danio, and it is possible to obtain genetically modified strains with 'glowing' colours. Thankfully, most fish keepers in this country would not be too happy with such fish being sold, and we have yet to see any on sale.
Danios are active fish, and will continually dart around the aquarium interacting with each other, searching for food, and swimming against any available flow of water. Because of this natural behaviour, the fish must be kept in groups comprising of at least six for the smaller species, and at least four or five for larger danios.
Under ideal conditions, it is quite easy to encourage spawning behaviour in danios, in which the fish may chase and embrace each other, dropping eggs to the substrate. In a community tank, or a tank containing several fish, it is unlikely to ever see any young, since the eggs are normally eaten before they can hatch. To breed danios and raise a reasonable amount of young you will need to set up a specific spawning tank, and do a little research into the variety you are attempting to spawn.
Danios need plenty of swimming space, so although they are not large fish, they are best kept in reasonably sized aquariums. The smallest of the species, such as Glowlight, Zebra, and Leopard Danios, can be kept in 60cm (2 foot) long tanks, although 75cm is best, and larger species should be kept in no less than 90cm (3 foot) long tanks.
As with any fish, the environment they are kept in should 'simulate and stimulate', meaning it should be similar to their natural environment in order to encourage natural behaviour and activity. Provide a few hiding spots and vegetation around the sides and edges of the aquarium, and if possible, create some areas of strong water movement, so that the danios can swim against the current if they feel the need.
Water conditions and feeding
Because danios originate from stream environments, they are quite used to changes in water conditions, and will settle into most variations of pH and hardness, providing the change is not too great. Another factor of their natural environment is a seasonal variation in temperature, and all danio species prefer cooler water, with some able to live happily in unheated aquariums. For most species, if you are mixing them with other tropical fish, it is best to aim for 24C (75F), or in unheated tanks, 18C (64F) or above.
The natural habitats of these fish are usually very clean and clear, so good filtration and regular water changes are required in the maintenance of any aquarium the fish are kept in. In particular, keep a close eye on nitrate levels, and make sure they remain below 50ppm.
Whilst danios are quick and eager feeders, and will take almost any food type, a good diet will improve their health and encourage natural spawning behaviour. Provide a basic diet of brand name dried foods, which will supply all the essential vitamins and minerals, and supplement this with a variety of frozen or live foods, which will be appreciated by all your fish.
Although danios are very sociable and peaceful fish, they may not be well suited to live with all community fish. Whilst the smaller danios can be kept with just about anything of a similar size, the larger species might be a little boisterous for some. Any of the larger danio species are therefore best kept with active and moderately sized or robust fishes such as barbs, larger tetras, or rainbowfish. Slow moving, delicate, or skittish species, will not appreciate a shoal of large danios charging around the aquarium.
The most popular and commonly kept of the danios are the smaller varieties, since these are the species best suited to the majority of community aquariums, and contain some of the most colourful varieties. The popular Zebra and Leopard Danios (Danio rerio
) are actually variations of the same species, although there is some debate over whether the Leopard Danio deserves separate classification. Both these fish will grow to only 4cm, are highly adaptable, can live in tropical or unheated tanks, and are available in long-finned varieties.
Rapidly catching up with these two long-standing fish is the Glowlight Danio (Danio choprai), a wonderfully coloured and marked fish with a bright orange horizontal stripe and vertical banding towards the tail fin. Glowlight Danios are even smaller, at just 3.5cm when fully grown. The colour of these fish seen when young and on sale will intensify as the fish matures and settles into an aquarium, making them an excellent addition for a peaceful community of small fishes, or as a contrasting shoal in a planted aquarium.
Equally as striking is the distinctive Spotted Danio (Danio kyathit), which has a more robust and contrasting pattern than the Leopard Danio, and is a little bigger at up to 5cm. Finally, the Pearl Danio (Danio albolineatus) is more iridescently marked fish, with no spotted or striped body markings. Whilst the Pearl Danio has been a popular fish for a very long time, and is a great aquarium fish, it has become less recognised amongst all the new danio species now available. In some shops, you may see a fish called a 'Rosy Pearl', or 'Rosy Danio', which is a separate species with more red around the fins and lower body.
The larger danio species have the same characters as the smaller varieties, but because of their size appear more boisterous in the aquarium, so they are more suited to communities of larger fish. There are several larger danio species, and many are imported under the names of others, so if you want to know exactly what you are getting, you may need to use a good fish identification book.
The most common of the larger danios is the Giant Danio (Devario aequipinnatus), which can grow up to 12cm, and a similar fish has been available recently, with slightly more defined markings, Davario assemensis will reach up to 10cm.
Two larger danio species that stand out are the Moustache Danio (Danio dangila), so called because of its long barbells, and the Bengal Danio (Danio devario) Despite being called the Bengal Danio, several species actually come from Bengal, and they may also be given the same common name. The Bengal Danio has quite distinctive markings and almost looks like a cross between a danio and a Buenos Aires Tetra, with a dark band on the tail fin and red finnage.