Taxonomy & naming
Kottelatia brittani was described by Herbert R. Axelrod in 1976 from material collected in the Segamat District of Johor, peninsular Malaysia, and placed at that time in the large catch-all genus Rasbora as Rasbora brittani. The Catalog of Fishes (Eschmeyer, the authority for valid names) records the current valid combination as Kottelatia brittani (Axelrod, 1976), the parenthetical authority marking its transfer out of Rasbora.
The genus Kottelatia was erected to receive this species when the genus Rasbora was progressively dismembered by phylogenetic revision; Rasbora in the old sense was shown to be polyphyletic, and multiple satellite genera — among them Boraras, Trigonopoma, Brevibora, and Kottelatia — were carved from it. Kottelatia is monotypic: brittani is its only species. The common name Brittan's rasbora, honouring the American ichthyologist Martin R. Brittan, who produced the foundational 1954 revision of Rasbora, persists in the aquarium literature despite the genus change.
Morphology
Brittan's rasbora is a small, slender, laterally compressed cyprinid reaching a maximum total length of approximately 2 in, though most aquarium specimens are somewhat smaller. The body is elongate and fusiform, with a slightly pointed snout and a small, terminal to slightly upturned mouth suited to surface and mid-water feeding. The coloration is relatively plain: a pale, translucent silvery body with a mid-lateral stripe of darker pigment running from behind the gill cover to the caudal peduncle, and an overall yellowish or straw flush on the flanks in good condition.
Sexual dimorphism is modest but present. Females are typically deeper-bellied than males and appear more full-bodied when gravid. Males are slimmer and may show slightly more intense coloration along the lateral stripe, particularly when in breeding condition.
Habitat
Kottelatia brittani is native to quiet, forested lowland streams and small tributaries of the southern Malay Peninsula (type locality: Segamat District, Johor, Malaysia) and Sumatra, where it is associated with the Batang Hari drainage in Jambi Province. Its preferred habitats are the shaded, slow-flowing or gently-moving reaches characteristic of lowland Sundaland forest streams: clear water with overhanging and marginal vegetation, leaf litter on the substrate, and little direct sunlight penetrating the canopy.
Water parameters at these sites tend toward the soft and mildly acidic end typical of Sundaland lowland drainage, though this species is more tolerant than some peat-swamp endemics of the region. FishBase and Seriously Fish both document a pH range of 6.0–7.5, a temperature range of 68–79 °F, and moderate hardness of 18–143 ppm — reflecting a fish that can inhabit both clearer, slightly harder streams and the softer waters closer to peat-swamp margins.
Feeding
In the wild, Brittan's rasbora is an opportunistic micropredator and omnivore typical of small-stream Sundaland cyprinids. Its diet consists primarily of small invertebrates — aquatic and terrestrial insects, small worms, and tiny crustaceans — taken from the water surface and mid-water column, supplemented with algae, plant matter, and fine organic detritus wherever available.
In the aquarium the species presents no feeding difficulties. It accepts high-quality dried flake and micro-pellet foods readily and benefits from regular provision of small live and frozen foods such as daphnia, micro-worms, mosquito larvae, and baby brine shrimp to maintain condition and natural behaviour. Because it is a gentle, non-aggressive feeder, care should be taken in a community setting to ensure it is not outcompeted at mealtimes by bolder tankmates.
Mating
Kottelatia brittani is an egg-scattering, non-guarding spawner — the reproductive strategy universal among danio and rasbora-tribe cyprinids. There is no pair bond, no nest construction, and no parental care of any kind. Spawning is typically triggered by rising temperatures, fresh-water additions, and increasing day length, mirroring the seasonal onset of rains that characterise its lowland Sundaland home.
Courtship consists of a male closely pursuing and driving a gravid female through the vegetation. When both fish are ready, they press together briefly among fine-leaved plants or at the substrate surface and release eggs and milt simultaneously. The act is brief and may be repeated multiple times during a single spawning session. Neither parent shows any interest in the eggs or larvae after release.
Breeding
Breeding Kottelatia brittani in the aquarium follows the standard approach for small Sundaland egg-scatterers. A separate, shallow spawning tank furnished with fine-leaved plants (Java moss or similar) or spawning mops is recommended, with soft, slightly acidic water (pH around 6.5, low hardness) and a temperature of 75–79 °F. A well-conditioned pair or small group of adults is introduced in the evening, and spawning commonly occurs in the morning hours.
According to observations documented on Seriously Fish, the actual spawning period lasts roughly 24 hours, with adhesive eggs hatching in approximately 18–28 hours at tropical temperatures. The larvae become free-swimming one to two days after hatching. Because the adults will readily consume eggs and fry, parents are best removed immediately after spawning concludes. First foods for the free-swimming fry should be infusoria or commercial micro-fry preparations, progressing quickly to newly hatched brine shrimp nauplii as the fry grow.
In the aquarium
Brittan's rasbora is an undemanding, peaceful species well suited to a soft-water planted community aquarium. It is a shoaling fish and should be kept in groups of at least six to eight individuals; a larger school produces more natural behaviour and reduces shyness. Given its gentle temperament and modest size, it is best housed with similarly placid companions — other small rasboras, dwarf gouramis, small corydoras, or similarly-sized peaceful cyprinids. Boisterous or nippy tankmates should be avoided.
The ideal setup replicates the shaded, well-planted lowland stream: a dark substrate, driftwood, leaf litter for tannin release and visual cover, and fine-leaved or floating plants to soften the light. Filtration should provide gentle flow rather than strong turbulence. Water parameters of pH 6.0–7.5 and temperature 68–79 °F (68–79 °F) are appropriate, with softer, slightly acidic conditions closer to the lower end of those ranges preferred for long-term health and breeding readiness.
Conservation
Kottelatia brittani is assessed as Least Concern (LC) on the IUCN Red List, with the most recent evaluation completed on 3 April 2020. The IUCN notes high resilience — a minimum population doubling time under 15 months — and low vulnerability to fishing pressure. The species has not been evaluated under CITES or the Convention on Migratory Species.
Despite the LC designation, its range is restricted to lowland forested stream systems in Johor (Malaysia) and Sumatra, habitats that face ongoing pressure from deforestation, agricultural conversion, and water extraction across Sundaland. The long-term health of this and many similar small-stream cyprinids of the region depends on the retention of riparian forest buffers and the integrity of lowland drainage systems that are among the most threatened freshwater environments on Earth.