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Dwarf Rasbora

Scientific Name: Boraras maculatus
Family: Cyprinidae, Subfamily Danioninae

About the Dwarf Rasbora

Species Type: Freshwater Fish
Category: Cyprinids

Care Level: Moderate. May tolerate only a narrow range of water parameters, have specific dietary requirements including frozen or even live foods, may have behaviors that severely limit potential tankmates or may require a specialized aquarium setup.

Origin: SE Asia: widely distributed in Peninsular Malaysia, limited populations in Thailand, Singapore, and perhaps Borneo and Sumatra. Occurs in dimly-lit blackwater streams connected to forest peat swamps.

Compatibility/Temperament: Very peaceful, must be kept in a group of at least eight but much preferably more. Given its small size it is best in smaller tanks as a group or with similar small fish such as the Trigonostigma rasbora species, dwarf cory species, dwarf loach species, Dario dario, etc. Best not kept with other species in the genus as they will likely cross-breed. Tends to be "lost" in larger aquaria, and will be under stress when maintained with larger fish.

Description

A very colourful fish for the smaller well-planted aquarium. Floating plants to dim the light are necessary, with a substrate of sand or fine gravel, with chunks of bogwood and branches. This species will swim throughout the aquarium, but tends to spend considerable time in the upper half of the tank. Dried leaves will offer tannins and provide a food source of micro-organisms especially for fry.

This species is easy to spawn. Females are rounder than males and usually slightly larger, and the males tend to be more colourful. Typical of the dwarf cyprinid species, this one is an egg scatterer and continual spawner, meaning that a small number of eggs will be laid almost daily if the fish are in good condition. No parental care is provided, but with thick plant growth some fry will likely survive without intervention from the aquarist. The fish has a lifespan of 3 to 5 years.

Variation in colour is evident in this species, and probably due to the different population locales. Some are much more vivid red than others. This fish is sensitive to water conditions, and partial water changes should not be so large as to result in any significant alteration in water chemistry.

The species was originally described as Rasbora maculata in 1904 by G. Duncker. In 1993, Kottelat & Vidthayanon erected the new genus Boraras for the (new) type species Boraras micros on the basis of morphology and reproduction methods, and also moved the four small-bodied Rasbora species into this genus. A sixth species has now been described (Conway & Kottelat, 2011). The name Boraras is an anagram of "Rasbora" referring to the reverse ratio of abdominal and caudal vertebrae in Boraras compared to Rasbora. The species epithet, Latin for "spotted," was changed from maculata to maculatus to agree in gender with the genus name.

All six species in this genus have a distinctive colouration and patterning. On a reddish background, in B. maculatus, B. micros and B. naevus there are three roundish black/dark brown blotches, one being a shoulder patch that is larger than the eye, a second at the origin of the anal fin, and the third on the caudal peduncle (at the base of the caudal fin). On B. brigittae and B. urophthalmoides there is a black/dark brown midlateral stripe and the caudal fin base blotch, and on B. merah there is an elongated blotch of the same colour on the anterior third of the body and then a much narrower midlateral line leading to the caudal fin base (Conway & Kottelat, 2011).

In the first phylogenetic analysis of the species in Boraras, Conway (2005) established the monophyletic lineage of this genus. Dr. Conway noted that the interrelationships of the five Boraras species remains unresolved, and no evidence was found to suggest that Boraras and Trigonostigma are closely related.

Very recent work by Tang, et al (2010) has clarified the phylogeny of the genera in the monophyletic subfamily Danioninae that includes the species within Rasbora, Boraras and Trigonostigma. Monophyletic means that all species are descended from a single common ancestor included within that clade.

References:

Conway, Kevin W. (2005), "Monophyly of the genus Boraras (Teleostei: Cyprinidae)," Ichthyological Exploration of Freshwaters, Vol. 16, No. 3, pp. 249-264.

Conway, Kevin W. and Maurice Kottelat (2011), "Boraras naevus, a new species of miniature and sexually dichromatic freshwater fish from peninsular Thailand (Ostariophysi: Cyprinidae)," Zootaxa, Vol. 3002, pp. 45-51.

Kottelat, Maurice and C. Vidthayanon (1993), "Boraras micros, a new genus and species of minute freshwater fish from Thailand (Teleostei: Cyprinidae)," Ichthyological Exploration of Freshwaters, volume 4 (no. 2), pp. 161-176.

Tang, K.L., M.K. Agnew, M.V. Hirt, T. Sado, L.M. Schneider, J. Freyhof, Z. Sulaiman, E. Swartz, C. Vidthayanon, M. Miya, K. Saitoh, A.M. Simons, R.W. Wood and R.L. Mayden (2010), "Systematics of the subfamily Danioninae (Teleostei: Cypriniformes: Cyprinidae)," Molecular Phylogenetics and Evolution, volume 57, pp. 189-214.

Dwarf Rasbora Diet

Feeds on insects, small crustaceans and zoo-plankton in nature; readily accepts prepared foods, with frozen daphnia and brine shrimp ideal.

Size

Attains 2.5cm (1 inch).

Minimum Tank Suggestion

5 gallon for a group.

Ideal water parameters for Dwarf Rasbora

Soft (< 5 dGH), acidic (pH below 7, preferably within the range of 4 to 6.5), temperature 24-26C/75-79F. All fish will be wild caught and require soft, acidic water.

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