Many are pretty. All are both elegant and peaceful. Some are easy to breed. Rasboras are the perfect community fish in so many ways. Yet only a few species have managed to gain a place in the “Top Twenty” league, leaving some very beautiful fish underrated and largely overlooked. As Cyprinids rasboras share a vast family with such popular favourites as the goldfish (Carrasius auratus), koi carp (Cyprinus carpio), danios, barbs, labeo “sharks”, and many other species familiar to the fishkeeper. There are undoubtedly vastly more of their family members worldwide kept in outdoor pools than aquariums! More incongruously they also have many coarse angling fish as close relatives.
Within the genus Rasbora we can find a range of diverse forms, from the rapier-like streamlined species, to quite disimilar looking deep bodied fish. Some species have prominent markings, or pretty colours – often combining both features. Others are more subtly marked and coloured. There is also a bunch of them lacking any exciting features to make them desirable to the hobbyist, and are largely uncollected.
There are few aquarium fish as a group which are so uniformly peaceful and easily maintained as the rasboras. Within the genus there are some species which are notoriously difficult to acclimatise to aquarium life when collected from the wild, but once the conditioning process is complete they will usually become resilient and even robust. In direct contrast other species take to unfamiliar water chemistry and general community aquarium life with ease. It is essential that any fish should be bought from apparently healthy looking stocks, and this is perhaps especially true of many of the rasboras. Even if your supplier properly conditions newly arrived fish before offering them for sale, a “home quarantine” tank in which the fish may be further conditioned and observed before releasing them into an established aquarium, is an invaluable asset. Wild caught rasboras frequently manifest “white spot” and “velvet” diseases during handling between catching (at source) and delivery to the point of retail sale. Both maladies are easily treated, of course, but need prompt attention when noted. Some species of rasbora react badly to recommended dosages of disease cure medication, and introducing such cures in half doses over a longer treatment period is advisable for them. Be warned that change of water chemistry for a few species can cause dramatic reactions, resulting in emaciated-looking fish with clamped fins and other symptoms typical of a sickly, stressed, and unhappy fish. Special consideration must be given to such species to guard against this problem. The new fish should be seen to be perky, full bodied, fresh and bright in appearance, and feeding freely before being moved into the community aquarium.
Very often breeding rasboras is a matter of luck . That is to say a compatible pair, once found, will produce regular spawnings in suitable surroundings, although not a few species seem willing to get on with procreation without any fuss. Water chemistry varies according to the location of wild caught fish but in general, for breeding, a soft slightly acidic water will be preferred. Fine leafed plants over which they can scatter their highly adhesive eggs will also be helpful. Suitable fine live foods will also be an invaluable conditioner for breeding fish. Hatching time is very short. Fry will appear after 24 to 30 hours, and grow rapidly when given the correct feeding. For everyday feeding most captive rasboras will be forced to join their diverse companions in the community aquarium to survive on the daily pinch of convenience dried food. The ability to do quite well on such an unvaried diet is an asset or a fault, depending on your point of view. The easy option may produce fish which lack the sparkle and healthily filled out body profile which the more cosseted communities will conspicuously display. The extra food costs are really small indeed, and it is just a little more time which is required to take the simple steps towards caring for the aquarium community more humanely and with hugely satisfying results. Live foods are always an exciting treat, but frozen “fresh” foods are similarly nutritious, and convenient, of course.
If the rasboras suffer from nipped fins or damaged body mucous at least the more tricky of the species will need to be removed from the community back to the quarantine tank for rest and treatment. Unattended it is likely that fungal or bacterial infections will plague the damaged fish with the risk of the infection then spreading to other vulnerable species.
Although there are so few species of rasbora regularly available from aquatic retailers there are two or three which are commonly available as popular stock items. The Harlequin (Rasbora heteromorpha) is certainly the best known of the group to the hobbyist and takes a high rating in the top twenty list. Harlequins can be difficult as new imports, but usually become easy aquarium subjects once acclimatised and settled into new surroundings. So this is No.1 in the rasbora popularity list. Number 2 is quite different. The Scissortail (Rasbora trilineata) is much larger, more streamlined in shape, lacking bright colours, but sharing the feature of having distinctive markings. This species will usually ship well after collection and normally needs only a short time in conditioning for aquarium life. Quite a number are also being bred for the hobby. No.3 on the list is largely there by default. The Slim Harlequin (Rasbora espei) is listed from Thailand and elsewhere simply as “Harlequin” on supplier’s price lists from source. If a scientific name is ventured it will frequently be incorrectly quoted as heteromopha. Juveniles of the two species certainly look very similar. But with maturity there is a marked difference. Anyone buying espei mistakenly for the true Harlequin should not be disappointed with the lovely mature fish. It does not deserve to live in the shadow of its well known relative. After these three placings it is difficult to suggest a fourth and onwards placing as so many other species jostle for the position. Aquarium hobbyists can be as fickle about their preferences as any teenager is about music choices. Redline rasboras (R. pauciperforata), for example, can be in such demand at a given time that it is difficult to keep enough supplies coming through the system. Another time and they may grow to maturity over months of being in a store’s stock tanks with hardly a buying customer showing interest in them.
This article has concentrated on those species most likely to be encountered by the fishkeeper, but it leaves a whole lot more undescribed. Altogether the genus Rasbora is a fascinating one to work with for the serious breeder, or a useful one from which to choose community fish for the average hobbyist. The author has never experienced an aggressive or bullying rasbora of any species. They are easy going mixers with other species for the peaceful community aquarium, from whichever part of the world they may come.
The Harlequin fish (Rasbora heteromorpha) must surely be familiar to any tropical fish fan. The range of natural habitats is widespread throughout South East Asia, but the Harlequin is primarily found in parts of Malaysia, Sumatra, Thailand, and Singapore. Some stocks are available from commercial breeders, but wild caught supplies are still essential to satisfy the huge demand for this lovely fish. Most of the world’s supplies are shipped out through Singapore, though the stock will probably have been collected from other sources. Although the Harlequin will survive well on a good dried-food diet, it needs a varied diet which includes live or frozen foods to truly thrive and deliver its best potential. Even in aquarium conditions this species is able to attain its full potential size of about 5 cms.
The Slim harlequin (Rasbora espei) is predominently shipped out of Thailand to the world’s fishkeepers. This mature fish illustrates the warm glow which the body can radiate, but the intensity is beyond the capability of a mere photograph. The black/blue “triangle” is less well defined compared to the true Harlequin and gives over more of the little body to be suffused by the ember-red colour. This species is usually more easily acclimatised to aquarium life than heteromorpha. Sometimes espei is offered as hengeli, a smaller species from Sumatra. At about 3 cms. for aquarium raised fish this is a small species. In nature it is possible to find specimens nearer to 5 cms.
The Scissortail rasbora (R. trilineata) is altogether a different configuration than the deep bodied “Harlequin” types. Here we have a typical elongated and streamlined “fish shape”. It is one of the most popular rasboras despite the complete lack of any bright colours. The tail is distinctive, as its popular name suggests. The black patch prominently displayed in each lobe of the forked caudal fin is backed with a stark white area. Being set on an otherwise see-through tail fin the feature is eye-catching. As the fish swims the tail lobes open and close with a slight scissor action. The highly reflective silver body catches front lighting most effectively, and the lateral line shines out with a burnished gold effect. Big adults might reach 10 cms, but will more usually attain about 7cms. in the aquarium.
Unlike the “standard” Scissortail, the Red scissortail (Rasbora caudimaculata) can, by contrast be a tricky fish to acclimatise to aquarium life, but once well established it rarely gives further problems. Some caution at clean-out time or water change time would be advisable, however. This is a beautifully marked fish with black edged scales. The black tips of the deeply forked caudal fin accentuates the warm orange area which fades back into clear finnage towards the caudal peduncle. Wild caught fish may exceed 15 cms. while aquarium raised specimens will usually just about reach 7 or 8 cms.
The Clown Rasbora (Rasbora kalachroma) is one of the most difficult popular rasboras to acclimate to aquarium life. Low lighting over a soft acidic water filled quarantine aquarium with plenty of plant cover will make a good start towards settling newly acquired specimens to domestic life. When the fish seem to be well settled begin to make part water changes, using water from the intended long-term aquarium to top up and thereby gradually introduce the different water condition to the fish. Do not waste your money to buy this species unless the stock looks to be in perfect condition. Sick Clown rasboras are troublesome patients which can regress rapidly once they have problems. But when acclimatised and cared for sensibly at the critical times of change to their surroundings they are capable of giving great beauty in return for that care without demanding anything more from their keeper than any other fish in the community. A mature size of about 8cms. is not unusual for the species.
The Fire rasbora (Rasbora vaterifloris) is another pretty rasbora, coming exclusively from Sri Lanka. The general profile shape is similar to that of the Harlequin. Acclimatisation of this species can be tricky. Unconditioned specimens should be shunned. The most often seen colour form of this stylish little fish is rosy-red. The “blue” form is encountered quite often too, and very occasionally a much darker red fish is shipped, although this latter form is now rarely seen in the UK market. This species is very prone to “White Spot” disease and needs prompt and carefully administered treatment to recover. Wild fish may be found at about 5 cms. long, but in the aquarium they are more likely to reach no more than about 4 cms.
One of the toughest rasboras is the Golden striped rasbora (Rasboras daniconius). Because it breeds quite freely and is common at source this species is always available from suppliers in South East Asia, but it is often dismissed as “too ordinary” and overlooked. But the bright golden lateral line emphasised by a black area below is undeniably striking. The tail carries a degree of ochre yellow colouring. The distinctive scale patterning of the upper body is attractive. This is a big, tough (but not rough), fish without particular demands needing to be met. It grows to about 20 cms in the wild. Aquarium specimens are more likely to be no more than about 10 to 12 cms.
Less under-rated is the Firetail rasbora (Rasbora borapetensis). But even this stylish fish is sometimes dismissed as too plain! Those who look rather more closely and decide to buy are usually delighted with their purchase when it is established in the home aquarium. They are invariably inexpensive to buy, and one of the hardier rasboras. The bright gold lateral line, underscored with black, is a striking enough feature, but the prominent red patch of colour at the base of the tail is very attractive. A maximum size of about 6 cms. in aquarium culture is normal.
The Green eyed rasbora (Rasbora dorsiocellata) is a tiny species. As the name suggests, it is the brightly reflecting lower part of the iris of the eye which is the main attraction of this species. The true colour is a bright green which rarely can be replicated in a photograph. The dorsal fin is also eye-catching with a white-edged black “flag” marking. This feature gives rise to an alternative popular name of Hi-spot rasbora. Although capable of reaching almost 8 cms. at maturity this species is rarely seen in excess of about 5 cms. in the aquarium.
The Redline rasbora (Rasbora pauciperforata) is one of the author’s favourite aquarium fish. The slender torpedo shaped body is complemented with slightly elongated finnage, giving and altogether streamlined appearance. As a pretty, elegant, and peaceful fish, this lovely species can vie with the rest for a well deserved place in the peaceful community aquarium. The main feature is, of course, the red line which runs from the upper lip, over the top of the eye, along the lateral line to the very tip of the outer edge of the caudal peduncle. Aquarium conditions need to be near perfect in order to coax out the very best of the fiery quality from the red line. Coming from soft acidic waters in Sumatra, this is the preferred water chemistry of the Redline rasbora, but it will acclimatise to other conditions quite well, albeit at the expense of the intense glow the lateral line of red is capable of radiating. Small groups or shoals of Redlines are particularly effective. Up to 5 cms. may be achieved by this stunning little beauty in the aquarium as well as in nature.
The Black striped rasbora (Rasbora agilis) is a species which the author has only ever received as “strangers” in shipments of other rasboras, and notably with Redlines. Although similar in overall shape to the Redline rasbora this species is even more slender and the finnage more elongated with fine pointing at the tips of dorsal, anal, and ventral fins. In place of the red line of pauciperforata the Black striped rasbora has a burnished gold lateral line emphasised by the black area below it. This golden line follows much the same path from nose to tail as the red line of pauciperforata. The super-streamlined body enables this species to be fast and elusive, or agile – as its scientific name suggests. The top size for aquarium raised fish or wild caught adults will be about 5 cms.
The tiniest of the rasboras is the Dwarf rasbora (Rasbora maculata). This is a superb little gem of a fish, but is so small that it will frequently be passed over as insignificant. But a small shoal of mature specimens will make their mark in the small-fish community, and give great pleasure to their keeper. The prominent black spots on the body, and black etching on the dorsal and anal fins, attracts the attention of the viewer, but it takes a closer look to appreciate the subtle colours which suffuse both the body and fins of the Dwarf rasbora. Not always easily acclimatised, this species will settle down well after the conditioning period. With a top size of 2 cms. their companions must be carefully chosen. To larger fish they are just more live food.
The Pygmy rasbora (R. urophthalma) is only marginally larger than R. maculata. It is usually received, however, at an even smaller size! This species is also capable of maturing into a very pretty fish, but the colours and markings are more subdued than those of maculata and less easily appreciated. At 3 cms in aquarium conditions they are good companions for the Dwarf rasbora. In the wild they are said to go to 4 cms.