Are rasboras the perfect community fish?

There are few aquarium fish as a group that are so uniformly peaceful and easily maintained as the rasboras. Via Stefan Maurer/Flickr

Rasboras are the perfect community fish in so many ways. Many are pretty. All are elegant and peaceful. Some are easy to breed. Yet only a few species have managed to gain a place in the “top twenty,” leaving some very beautiful fish both underrated and largely overlooked.

As cyprinids, rasboras share a vast family with such popular favorites as the goldfish (Carrasius auratus), koi (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 ponds than in aquariums!

Within the genus Rasbora we can find a range of diverse forms, from streamlined species to very different looking deep-bodied fish. Some species have prominent markings or attractive colors — often combining both features. Others are more subtly marked and colored. There are also a number of them lacking any exciting features, making them less desirable to hobbyists, and thus largely unavailable in the aquarium trade.

There are few aquarium fish as a group that are so uniformly peaceful and easily maintained as the rasboras. Within the genus there are some species that are notoriously difficult to acclimatize to aquarium life when collected from the wild, but once the conditioning process is complete, they will usually become resilient and even robust aquarium inhabitants. In direct contrast, other species accept unfamiliar water chemistry and general community aquarium life with ease.

In general, it is essential that any fish should be bought from apparently healthy-looking stocks, but 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 aquarium 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 collection and delivery to the point of retail sale. Both maladies are easily treated, of course, but need prompt attention when observed. Some species of rasbora react badly to recommended dosages of medications, so introducing such cures in half doses over a longer treatment period is advisable for them.

Be warned that a 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, unhappy fish. Special consideration must be given to such species to guard against this problem. The new fish should be seen to be alert, full bodied and healthy in appearance, and feeding freely before being moved into the community aquarium.

When it comes to breeding rasboras, a compatible pair — once found — will produce regular spawnings in suitable surroundings. A number of species seem willing to get on with procreation without any fuss at all.

Water chemistry varies according to the location of wild-caught fish, but in general, for breeding, soft and slightly acidic water is preferred. Fine-leaved aquatic 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 foods.

For everyday feeding, most captive rasboras will be forced to join their diverse companions in the community aquarium and survive on the daily pinch of 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 that lack the sparkle and healthy filled-out body profile that are more common to fish that receive a varied diet. The additional food costs are really small indeed, and the results are well worth it. Live foods are always an exciting treat, but frozen foods are similarly nutritious and convenient.

If the rasboras suffer from nipped fins or damaged body mucous, at least the more demanding of the species will need to be removed from the community back to the quarantine aquarium 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 few species of rasbora regularly available from aquatic retailers, there are two or three that are commonly available as popular stock items. The harlequin (Rasbora heteromorpha) is certainly the best known of the group to the hobbyist. Harlequins can be difficult as new imports, but usually become easy aquarium subjects once acclimatized and settled into new surroundings.

The harlequin rasbora is found in a range of natural habitats throughout Southeast Asia, but 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 that includes live or frozen fish foods to truly thrive and deliver its best potential. In suitable aquarium conditions this species is able to attain its full potential size of about 2 inches.

If the harlequin is number one on the rasbora popularity list, number two is quite a different fish. The scissortail (Rasbora trilineata) is much larger, more streamlined in shape, and lacks bright colors, but it does share the feature of having distinctive markings. This species will usually ship well after collection, and normally needs only a short time of conditioning for aquarium life. Quite a number are also being commercially bred for the hobby.

The tail is distinctive, as its popular name suggests. The black patch prominently displayed in each lobe of the forked tail fin is backed with a stark white area. Being set on an otherwise see-through fin, this black on white 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 4 inches, but will more usually attain about 2¾ inches in the aquarium.

Number three on the list is largely there by default. The slim harlequin (Rasbora espei) is listed from Thailand and elsewhere simply as “harlequin” on suppliers’ price lists. If a scientific name is ventured it will frequently be incorrectly quoted as Rasbora 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.

As an adult, this fish exhibits the warm glow that the body can radiate, but the intensity is beyond the capability of a mere photograph. The black/blue “triangle” is less well defined compared with the true harlequin, and allows more of the little body to be suffused by the ember-red color. This species is usually more easily acclimated to aquarium life than the harlequin. Sometimes espei is offered as hengeli, a smaller species from Sumatra. At about 1 inch for aquarium-raised fish, this is a small species. In nature, it is possible to find specimens nearer to 2 inches.

After these three placings it is difficult to suggest a fourth and onward because 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. At other times they may grow to maturity over months of being in a store’s stock aquariums with hardly a buying customer showing interest in them. I’ll cover some of the other rasbora species for those aquarists lucky enough to find them.

The firetail rasbora (R. borapetensis) is a stylish fish that is sometimes dismissed as being 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. This species is 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 color at the base of the tail is also very attractive. A maximum size of about 2 1/3 inches in aquarium culture is normal.

The tiniest of the rasboras is the dwarf rasbora (R. maculata). This is a superb little gem of a fish, but it is so small that it will frequently be passed over as insignificant. However, a small school of mature specimens will make their mark in the small fish community, and will give great pleasure to their keepers. The prominent black spots on the body and black etching on the dorsal and anal fins attract the attention of the viewer, but it takes a closer look to appreciate the subtle colors that suffuse both the body and the fins of the dwarf rasbora. Not always easily acclimated, this species will settle down well after the conditioning period. With a top size of ¾ inch, their companions must be carefully chosen. To larger fish they are little more than live food.

Unlike the “standard” scissortail, the red scissortail (R. caudimaculata) can, by contrast, be a tricky fish to acclimate to aquarium life. Once well established, however, it rarely gives further problems. This is a beautifully marked fish with black-edged scales. The black tips of the deeply forked tail fin accentuate the warm orange area that fades back into clear finnage toward the base of the tail fin. Wild-caught fish may exceed 6 inches, while aquarium raised specimens will usually just about reach 2¾ to 3 inches.

The clown rasbora (R. kalachroma) is one of the most difficult popular rasboras to acclimate to aquarium life. Low lighting over a quarantine aquarium filled with soft, acidic water with plenty of aquatic plant cover will make a good start toward settling newly acquired specimens to domestic life. When the fish seem to be well settled, begin to make partial water changes using water from the intended display aquarium to top off and thereby gradually introduce the different water conditions 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 that can regress rapidly once they have problems. But, when acclimated and cared for sensibly, they are capable of giving great beauty in return for that care without demanding anything more from their keepers than any other fish in the community. A mature size of about 3 inches is not unusual for this species.

The pygmy rasbora (R. urophthalma) is only marginally larger than R. maculata. It is usually imported, however, at an even smaller size! This species is also capable of maturing into a very pretty fish, but the colors and markings are more subdued than those of maculata and less easily appreciated. At 1 inch they are good companions for the dwarf rasbora. In the wild, they are said to reach up to 1½ inches in length.

The fire rasbora (R. vaterifloris) is another attractive species, coming exclusively from Sri Lanka. The general profile shape is similar to that of the harlequin. Acclimation of this species can be tricky. Specimens in poor condition should be avoided. The most often seen color form of this stylish fish is rosy red. The “blue” form is encountered quite often as well, and very occasionally a much darker red fish is shipped, although this latter form is now rarely seen, at least in the United Kingdom market.

This species is very prone to “white spot” (ich) disease and needs prompt and carefully administered treatment to recover. Wild fish may be found at about 2 inches long, but in the aquarium they are more likely to reach no more than about 1½ inches.

One of the toughest rasboras is the golden striped rasbora (R. daniconius). Because it breeds quite freely and is common collected, this species is always available from suppliers in Southeast Asia, but it is often dismissed as “too ordinary” and thus overlooked. But, the bright golden lateral line emphasized by a black area below is undeniably striking. The tail carries a degree of ochre yellow coloring. The distinctive scale patterning of the upper body is attractive. This is a big, tough (but not rough) fish without any particular demands needing to be met. It grows to about 8 inches in the wild, but aquarium specimens are more likely to be no longer than about 4 to 5 inches.

The green eyed rasbora (R. dorsiocellata) is a tiny species. As the name suggests, it is the brightly reflecting lower part of the iris of the eye that is the main attraction of this species. The true color of this freshwater fish is a bright green that can rarely be replicated in a photograph. The dorsal fin is also eye-catching with its white-edged black “flag” marking. This feature gives rise to an alternative popular name of hi-spot rasbora. Although capable of reaching almost 3 inches at maturity, this species is rarely seen in excess of about 2 inches in the aquarium.

The redline rasbora (R. pauciperforata) is one of my favorite aquarium fish. The slender, torpedo-shaped body is complemented with slightly elongated finnage, giving an 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 that runs from the upper lip, over the top of the eye, and along the lateral line to the very tip of the outer edge of the base of the tail fin. Aquarium conditions need to be near perfect in order to coax out the very best of the fiery quality of this red line. Coming from soft, acidic waters in Sumatra, this is the preferred water chemistry of the redline rasbora, but it will acclimate 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 schools of redlines are particularly effective. Lengths up to 2 inches may be achieved by this stunning little beauty in the aquarium, as well as in nature.

The black striped rasbora (R. agilis) is a species that I have only ever received as “undescribed” in shipments of other rasboras — notably with redline rasboras. 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 the dorsal, anal and ventral fins.

In place of the red line of pauciperforata, the black striped rasbora has a burnished gold lateral line emphasized 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 and wild-caught adults will be about 2 inches.

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.

I have never experienced an aggressive or bullying rasbora of any species. They are easygoing and compatible with other species for the peaceful community aquarium.

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