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Sawbwa resplendens ANNANDALE, 1918

Etymology

Sawbwa: from a native word meaning ‘prince, chief’.

resplendens: from the Latin resplendens, meaning ‘shining, glittering’.

Classification

Order: Cypriniformes Family: Cyprinidae

Distribution

Endemic to the isolated mountain lake of Inle and surrounding watershed in Shan State, eastern Myanmar.

The lake lies in a karstic valley almost 900m above sea level in the Shan Plateau region and is home to many endemic animals including nine species of fish and numerous gastropods.

Habitat

The water in Lake Inle is clear, shallow (2-3 metres deep in most places) and has a very fertile, loamy substrate.

It’s famed for its stilted villages and local fishermen known as Intha who row their boats using only one leg.

These people, thought to have migrated from the south of Myanmar in the late 1300s, use naturally-occurring floating ‘islands’ consisting of tangles of various plant species as gardens.

These islands form a wide raft around the lake margins and the Intha take them as required, removing the aerial leaves and cutting them into sections.

Bamboo poles are added for support allowing fruit, vegetables, rice and flowers to be produced in commercial quantities. The gardens rise and fall with the water level and have come to form the habitats of many fish which take shelter among the tangle of roots and plant stems at their base.

Macrophytes also grow densely in the crystal-clear water and include Ceratophyllum and Elodea-like species.

S. resplendens is mostly collected around the margins of the lake where grass and reed-like plants proliferate and the floating islands form thick mats composed of both live and dead vegetation.

As the lake is situated in a karstic zone it contains neutral to slightly alkaline water with the pH value varying between 7.5 – 8.0. Its main outlet is a seasonal stream known as the Balu Chaung which floods at certain times of year allowing the transfer of fishes to pools and ponds close to Loi Kaw.

During drier months these are disconnected, isolating small populations of several species. We’ve yet to obtain detailed information regarding these habitats but expect them to be characterised by similarly sluggish, clear water with dense marginal/submerged plant growth.

Maximum Standard Length

Normally quoted as 20 – 25 mm but aquarium specimens can attain 30 – 35 mm.

Aquarium SizeTop ↑

Despite its small size we wouldn’t keep a group of these in anything measuring less than 60 ∗ 30 cm litres due to the sometimes combative behaviour of dominant males (see ‘Behaviour and Compatibility’).

Maintenance

Best kept in a heavily-planted set-up, preferably with a dark substrate. The broken lines of sight that exist in such a display allow it to display natural behaviour as well as helping to reduce skittishness.

Floating plants are a useful addition but driftwood and dried leaf litter are best avoided as the tannins they release are not a feature of its natural waters.

Use gentle filtration; an air-powered sponge-style unit should prove adequate.

Water Conditions

Temperature: Temperatures in Lake Inle have been recorded to vary between 20 – 24 °C.

pH: Will tolerate slightly acidic conditions but a value of 7.0 – 8.0 is preferable.

Hardness: Best kept in slightly harder water of 179 – 357 ppm.

Diet

Likely to feed on small invertebrates, algae 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 DaphniaArtemia and suchlike will not only result in the best colouration but encourage the fish to come into breeding condition.

Newly-imported specimens are often in poor condition and can be difficult to acclimatise to aquarium life.

Small live foods are therefore recommended as an initial diet with dry and frozen products being introduced as the fish become settled.

Behaviour and CompatibilityTop ↑

Very peaceful towards other species but not an ideal community fish due to its small size and aggressive interactions between rival males.

It does best when maintained alone or with active, similarly-sized tankmates that enjoy comparable water conditions.

A community based around species from Lake Inle would make an interesting project with suitable species available in the trade including Danio erythromicron, Devario auropurpurea, Parambassis lala, and Yunnanilus brevis.

Though gregarious by nature it’s a shoaling rather than schooling species which develops a distinct pecking order.

Males tend to be engaged in a continual battle for dominance, particularly when maintained in small numbers or in the presence of few females.

The best way to minimise this behaviour is to purchase more females than males; a ratio of 4:1 or more being ideal.

Unfortunately females can be hard to find on sale because exporters often prefer to ship only the more colourful males.

At the very least try to purchase it in sexed pairs or use a larger tank arranged in such a way that many broken lines of sight are provided.

Sexual Dimorphism

Males are more colourful possessing red tips to the snout and caudal-fin plus a bluish sheen on the flanks.

Females are much plainer with a uniformly olive/pale brownish colour pattern except for a dark marking just anterior to the anal-fin, and appear noticeably rounder in the belly when in spawning condition.

Reproduction

This species naturally deposits eggs among aquatic vegetation or filamentous algae but in the aquarium synthetic spawning mops can also be used if you prefer.

Apparently the most favourable results are obtained when a group of adults is maintained together as a group and the substrate checked daily for eggs, since the adults tend to eat their spawn.

Temperature also appears important, with the fish failing to spawn at values in excess of 77°F/25°C, while general hardness should be at least 20° for both successful spawning and rearing of fry.

SF member Mike Vulis notes that although the fry are relatively large they require microscopic food for at least 5-6 days before they will accept larger fare such as Artemia nauplii, apparently because they are only capable of digesting quite small amounts of food at a time.

Small meals offered several times a day are therefore recommended for optimal growth, and it is important to observe the fry closely as they absorb their yolk sacs since they require food almost immediately once free-swimming.

Thanks to Michael Vulis.

NotesTop ↑

S. resplendens may be seen on sale under several trade names including ‘Asian rummynose’, ‘rummynose rasbora’ and ‘naked microrasbora’.

These can give the false impression that it’s related to members of the genera Rasbora and Microrasbora but phylogenetic studies have shown to be more closely-affiliated with Puntius, Pethia, and other related genera. The genus is currently monotypic and likely to remain that way.

The small adult size 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, e.g., 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”.

References

  1. Annandale, N., 1918 - Records of the Indian Museum (Calcutta) v. 14: 33-64
    Fish and fisheries of the Inlé Lake.
  2. Fang, F., M. Norén, T. Y. Liao, M. Källersjö, and S. O. Kullander, 2009 - Zoologica Scripta 38(1): 1-20
    Molecular phylogenetic interrelationships of the south Asian cyprinid genera Danio, Devario and Microrasbora (Teleostei, Cyprinidae, Danioninae).
  3. Liao, T. Y., Kullander, S. O. and F. Fang, 2009 - Zoologica Scripta 39(2): 155-176
    Phylogenetic analysis of the genus Rasbora (Teleostei: Cyprinidae).
  4. Rüber, L. , M. Kottelat, H. H. Tan, P. K. L. Ng, and R. Britz, 2007 - BMC Evolutionary Biology London 7: 1-10
    Evolution of miniaturization and the phylogenetic position of Paedocypris, comprising the world's smallest vertebrate.

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