Boraras brigittae - Mosquito Rasbora

Cyprinidae

Appears to be endemic to southwestern Borneo though occurence records are scant. The type locality is given as Bandjarmasin, a port town in the Indonesian province of South Kalimantan (Kalimantan Selatan).

Inhabits black water streams and pools associated with ancient forest peat swamps. The water is stained brown due to the release of tannins and other chemicals released by decomposing organic matter and the substrate scattered with fallen leaves, twigs and branches. Such environments characteristically contain very soft (negligible hardness), acidic (pH as low as 4.0) water and are often dimly-lit due to the forest canopy above and dense marginal vegetation. Across much of Southeast Asia these precious biotopes are under threat from rubber/palm oil plantations, building developments and other human activities.

Around 1.2"/3.5cm.

Though small it still needs space to swim and dominant males will form temporary territories when spawning so a group is best kept in a tank measuring at least 18" x 10" x 10"/45cm x 25cm x 25cm/29.5 litres.

Best kept in a densely-planted tank and is an excellent choice for the carefully-aquascaped set-up. The addition of some floating plants and driftwood roots or branches to diffuse the light entering the tank also seems to be appreciated and adds a more natural feel. Filtration does not need to be particularly strong as it mostly hails from sluggish waters and may struggle if there is a fast current.

To see it at its best a biotope-style set-up can also make an interesting project. A soft, sandy substrate is probably the best choice to which can be added a few driftwood roots and branches, placed in such a way that plenty of shady spots are formed. If you can't find driftwood of the desired shape common beech or oak is safe to use if thoroughly dried and stripped of bark.

The addition of dried leaf litter (beech, oak or Ketapang almond leaves are all suitable; we like to use a mixture of all three) would further emphasise the natural feel and as well as offering even more cover for the fish brings with it the growth of microbe colonies as decomposition occurs. These tiny creatures can provide a valuable secondary food source for fry whilst the tannins and other chemicals released by the decaying leaves are thought to be beneficial for blackwater fish species such as this. Leaves can be left in the tank to break down fully or removed and replaced every few weeks.

Allow the wood and leaves to stain the water. A small net bag filled with aquarium-safe peat can also be added to the filter or hung over the edge of the tank to aid in the simulation of black water conditions. Alternatively obtain some genuine peat fibre and simply drop a few handfuls into the tank. This will become completely saturated with water after a few days and sink to the bottom where it can look really effective. Provided a good routine of water maintenance is practiced no adverse effects should occur using either peat or leaves in an aquarium.

Fairly dim lighting should be used to simulate the conditions the fish would encounter in nature. You could add some Asian plants that can survive under such conditions such as Microsorum pteropus, Taxiphyllum barbieri or Cryptocorynes. A few patches of floating vegetation would be really useful to diffuse the light entering the tank too. Do not add this fish to a biologically immature tank as it can be susceptible to swings in water chemistry.

77 - 82°F/25 - 28°C

5.0 - 7.0

5 - 10°H

As with other Boraras species it is likely to be a micropredator feeding on small insects, worms, crustaceans and other zooplankton in nature. In the aquarium it will accept dried foods of a suitable size but should not be fed these exclusively. Daily meals of small live and frozen fare such as Daphnia, Artemia along with good quality flakes and granules will result in the best colouration and encourage the fish to come into breeding condition.

This species is very peaceful but does not make an ideal community fish due to its small size and rather timid nature. It will do best when maintained alone or with other diminutive species such as Microdevario, Sundadanio, Danionella, Eirmotus, Trigonostigma, pygmy Corydoras and small Loricariids such as Otocinclus. It also makes an ideal companion for shy anabantoids such as Sphaerichthys, Parosphromenus or the more diminutive Betta species and in a planted set-up can be housed alongside freshwater shrimp of the genera Caridina and Neocaridina. We don't recommend keeping it with other Boraras as hybridisation might occur.

It's a shoaling species by nature and really should be kept in a group of at least 8-10 specimens. Maintaining it in decent numbers will not only make the fish less nervous but will result in a more effective, natural-looking display. Males will also display their best colours and some interesting behaviour as they compete with one other for female attention.

Mature females are noticeably rounder-bellied and often a little larger than males. Males are generally more attractive with dominant individuals often displaying intense colouration.

Like many small cyprinids this species is an egg-scattering, continuous spawner that exhibits zero parental care. That is to say when in good condition and in the presence of both males and females relatively small numbers of eggs will be laid daily. In a well-furnished, mature aquarium it is therefore possible that small numbers of fry may start to appear without human intervention.

However if you want to increase the yield of fry a slightly more controlled approach is required. The adult group can still be conditioned together but one or more separate, say 12" x 8" x 8"/30cm x 20cm x 20cm/12.5 litre containers should also be set up. These should be very dimly lit with the base either left bare or covered with some kind of mesh of a large enough grade so that any eggs that fail to adhere to the plant can pass through but small enough so that the adults cannot reach them. The widely available plastic 'grass'-type matting can also be used and works very well. The water itself should be of pH 5.0-6.5, 1-5°H with a temperature towards the upper end of the range suggested above. A decent-sized clump of Java moss or other fine-leaved plant should also be added filling perhaps half the available space. Filtration is not really necessary but you can use a small, air-powered sponge filter if you prefer.

Two or three pairs of well-conditioned adult fish should then be introduced to each container. It is wise to make the transfer slowly in order to avoid excessive levels of stress but if conditions are to their liking they should begin to spawn the following morning. While this species certainly will eat its eggs it appears not to actively hunt for them as is the case with many small Puntius and other related species. Once spawning has commenced it should continue on a daily basis.

The pair(s) should be left in situ for no more than a couple of days before being removed as the first eggs should hatch by the second day after the initial spawning. The tiny young will survive on their yolk sacs for another 24 hours or so after which they will require Paramecium or other microscopic food. After a week to ten days they should be large enough to accept Artemia nauplii/microworm etc. As the days pass additional fry should start to appear from later spawning events. It's best to wait a week or two before starting to perform small water changes in order to avoid unduly shocking the young fish.

To many Boraras brigittae is the most attractive member of the genus which perhaps explains why it is so common to see B. urophthalmoides (mis)labelled with the name in the trade. While it might be confused with the 'red/orange' colour form of urophthalmoides at first glance brigittae is easily identifiable by its larger adult size, lack of distinct dark blotch at the caudal peduncle, comparitively short, often broken lateral stripe and overall brighter/more uniformly red patterning. It is sometimes seen on sale with the alternative trade name of 'chili rasbora'.

Boraras was erected in 1993 in order to separate a small band of species from the larger Rasbora grouping on the basis of differences in morphology and reproductive strategy. In older literature they are therefore referred to as members of Rasbora and following Liao et al. (2009) the genus is a member of the rasborin sub-group within the subfamily Danioninae (the other sub-group contains the danionins). This group is further subdivided into six clades (clusters of closely-related species) of which Boraras (or at least Boraras brigittae; the only species involved in the study) is included in "clade three" alongside Horadandia atukorali , Rasboroides vaterifloris , Trigonostigma heteromorpha  and three species previously included in Rasbora but moved into new genera by the authors; Trigonopoma gracile , T. pauciperforatum  and Rasbosoma spilocerca  (note: since the new names have yet to find general acceptance the latter are all still listed within Rasbora here on Seriously Fish). Of these it was found to form a monophyletic group with Rasboroides meaning these two derived from the same common ancestor. The results for Boraras brigittae and T. heteromorpha  were found to be inconclusive in some respects and further work regarding their phylogenetic position was recommended.

The small adult size in Boraras species evolved via a process known as miniaturisation, characterised by sexually mature adults with a significantly reduced size of less than 20mm SL. Among bony fishes cyprinids are one of the few groups in which this phenomenon occurs repeatedly with all Barboides, Danionella, Microdevario, Microrasbora, Horadandia, Boraras, Paedocypris, Sawbwa and Sundadanio species representing miniaturised taxa along with a few members of Danio, Laubuca and Rasbora. All show a preference for still or slow-moving waters, often in nutrient-poor habitats such as forest peat swamps.

The anatomical structure of miniaturised cyprinids can vary greatly; there are two principle 'groupings' with some species possessing intermediate features to some degree. The first contains those fishes which though small are essentially proportionally dwarfed versions of their larger relatives e.g. Barboides, Microdevario, Microrasbora, Horadandia, Boraras, Sawbwa, Sundadanio, Danio, Laubuca and Rasbora.

The other includes those in which anatomical development stops at a point where adult still resemble a larval form of their larger ancestor i.e. Danionella and Paedocypris. The latter are usually referred to as 'developmentally truncated' or 'paedomorphic' and are thought to have evolved via a process known as 'progenetic paedomorphosis' i.e. paedomorphosis brought about by accelerated maturation. They typically exhibit a simplified skeletal structure along with species-specific morphological peculiarities such as the tooth-like projections in male Danionella dracula . Britz et al. (2009) consider that developmental truncation may have facilitated the development of such novelties "by freeing large parts of the skeleton from developmental constraints, dissociating developmentally linked pathways and creating a greater potential for more dramatic changes".

Boraras species from the Malay Archipelago (Boraras brigittae, B. maculatus  and B. merah ) tend to have a slimmer, more elongate body profile than those from Indochina (B. micros , B. urophthalmoides, B. sp. 'South Thailand') which may assist when attempting to identify them.

Literature cited

1. Conway, K. W. 2005 - Ichthyol. Explor. Freshwaters, Vol. 16, No. 3, pp. 249-264.
   Monophyly of the genus Boraras (Teleostei: Cyprinidae).
2. Mayden, Richard L.; Tang, Kevin L.; Conway, Kevin W.; Freyhof, Jörg; Chamberlain, Sarah; Haskins, Miranda; Schneider, Leah; Sudkamp, Mitchell; Wood Robert M.; Agnew, Mary; Bufalino, Angelo; Sulaiman, Zohrah; Miya, Masaki; Saitoh, Kenji; He, Shunping. 2007 - J. Exp. Zool. (Mol. Dev. Evol.) 308B: 1–13.
   Phylogenetic relationships of Danio within the order Cypriniformes: a framework for comparative and evolutionary studies of a model species.
3. www.petfrd.com
4. www.fishbase.org
5. Liao, T. Y., Kullander, S. O. and F. Fang. 2009 - Zoologica Scripta Early View (Articles online in advance of print).
   Phylogenetic analysis of the genus Rasbora (Teleostei: Cyprinidae).