Horadandia atukorali

Cyprinidae

Native to Sri Lanka and southern India where it´s restricted to Kerala and Tamil Nadu states plus the Union State of Puducherry (formerly Pondicherry). A subspecies, H. a. brittani, was described by Devi and Menon in 1992 from Pathiramanal Island, Vembanad Lake, Kerala but was brought into synonymy by Menon just a year later.

According to Talwar & Jhingran (1991) it shows a preference for sluggish and still waters such as rice paddies, swamps and weedy ponds, tending to be most common in flood plains and other lowland areas. It's also been collected from ditches with dense growths of submerged vegetation. In Kerala species inhabiting similar environments include Carinotetraodon imitator, Laubuca dadiburjori, Aplocheilus parvus, Pseudosphromenus dayi  and P. cupanus.

20 - 30 mm.

A group is best kept in a tank measuring upwards of 18" x 12" x 12"/45cm x 30cm x 30cm/42.5 litres

This species can appear a little devoid of colour if kept in sparse surroundings but makes a superb addition to the heavily-planted aquarium. This can be further decorated with twisted roots, branches, smooth rocks and stones and a few handfuls of leaf litter, if you prefer. A dark substrate is best and consider the addition of some floating vegetation to provide shade. Filtration should be relatively gentle.

68 - 78.8°F/20 - 26°C.

Aim for a value of 5.5 - 7.5.

2 - 12°H

Chiefly 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.

It's a schooling species by nature and should be kept in a group of at least a dozen specimens. Maintaining it in numbers will not only make the fish less nervous but will result in a more effective, natural-looking display.

Mature females are noticeably rounder-bellied and usually larger than males.

This species hasn't been bred often in aquaria but the few reports that do exist suggest it's not too difficult. 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 eggs will be laid regularly. In a well-furnished, mature aquarium it's therefore possible that small numbers of fry may start to appear without 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 smaller, say 12" x 8" x 8"/30cm x 20cm x 20cm/12.6 litre containers should also be set up and filled with aged water. Fill most of the available space with fine wool mops, Java moss or other fine-leaved plant. Neither lighting nor filtration is necessary although you can install a small air-powered sponge filter if you prefer.

A small group or single pair of adults can then be introduced. The eggs are only mildly adhesive, tending to fall to the base of the tank from where they can easily be siphoned into a separate container using a length of air line or similar. Alternatively the adults can be removed once eggs are spotted. Incubation usually takes between 47 - 54 hours (Sado and Kimura, 2005) with the fry initially requiring microscopic foods such as Paramecium until big enough to accept Artemia nauplii, microworm or dried products of a suitably fine grade.

This genus is monotypic and distinguished from other cyprinid taxa by a combination of a moderately compressed, elongated body with two rows of teeth on the lower pharyngeal (throat) bone and lacking barbles, visible lateral line and a symphyseal knob on the lower jaw (Talwar & Jhingran, 1991). Its 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 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".

Following Liao et al. (2009) Horadandia 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 H. atukorali is included in "clade three" alongside Boraras brigittae , 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 B. brigittae  and T. heteromorpha  were found to be inconclusive in some respects and further work regarding their phylogenetic position was recommended.

Literature cited

1. Britz, R. 2009 - Zootaxa 2277: 53-60.
   Danionella priapus, a new species of miniature cyprinid fish from West Bengal, India (Teleostei: Cypriniformes: Cyprinidae).
2. Britz, R. , K. W. Conway, and L. Rüber. 2009 - Proceedings of the Royal Society of London, Series B - Biological Sciences. (Published online 11 March 2009).
   Spectacular morphological novelty in a miniature cyprinid fish, Danionella dracula n. sp.
3. 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).
4. Rema Devi, K. 1996 - J. Bomb. Nat. Hist. Soc. 93(2): 303-304.
   Extension of range of distribution of Horadandia atukorali Deraniyagala (Pisces: Cyprinidae: Rasborinae) to Pondicherry and Tamil Nadu.
5. Rüber, L. , M. Kottelat, H. H. Tan, P. K. L. Ng and R. Britz. 2007 - BMC Evol. Biol. London. 7: [1-10].
   Evolution of miniaturization and the phylogenetic position of Paedocypris, comprising the world's smallest vertebrate.
6. Sado, T. and S. Kimura. 2004 - Ichthyol. Res. 52(2): 152-157.
   Developmental morphology of the cyprinid fish Horadandia atukorali.
   
7. Talwar, P. K. and A. G. Jhingran. 1991 - A.A. Balkema, Rotterdam. 541 p.
   Inland Fishes of India and Adjacent Countries. Vol 1.