Malabar danio

The Malabar danio (Devario malabaricus) is a species of freshwater ray-finned fish belonging to the family Danionidae. Originating in Sri Lanka and the west coast of India, the fish has been circulated throughout the world through the aquarium fish trade. It grows to a maximum length of 6 in (15 cm) but rarely exceeds 4 in (10 cm) in a home aquarium.

Malabar danio
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cypriniformes
Family:	Danionidae
Subfamily:	Danioninae
Genus:	Devario
Species:	D. malabaricus
Binomial name
Devario malabaricus (Jerdon, 1849)
Synonyms
Perilampus malabaricus Jerdon, 1849 Danio malabaricus (Jerdon, 1849) Puntius malabaricus (Jerdon, 1849) Perilampus canarensis Jerdon, 1849 Perilampus mysoricus Jerdon, 1849 Danio micronema Bleeker, 1863 Perilampus aurolineatus Day, 1865 Paradanio aurolineatus (Day, 1865) Eustira ceylonensis Günther, 1868 Perilampus ceylonensis (Günther, 1868)

The Malabar danio is found in tropical climates in a wide variety of waters, from mountain streams to small pools, but it prefers flowing waters. It is an active, schooling fish that prefers to be in groups. Its diet consists of insects and plant matter.

The species was earlier incorrectly considered a synonym of Devario aequipinnatus, which is a valid name for a different species.

Species Description

The Malabar danio is a relatively small, brightly colored fish with stripes that may be broken up. Adults are commonly found to be 8.0 cm long.¹ Their fusiform bodies are elongated and laterally compressed with a superior mouth. The dorsal fin sits posteriorly with 12 to 16 dorsal soft rays. The anal fin is composed of 15 to 20 soft rays. They also possess 5-6 irregular, vertical bars on the anterior half of their bodies.

Malabar danios possess a danionin notch. Characteristic of the family Danionidae, this notch is an indentation of the lower jaw.⁹ Fish in the genus Devario are characterized by a short maxillary barbel, a P stripe that extends on the median caudal fin rays, and a short and wide premaxillary ascending process with a protrusion connecting to the kinethmoid. The kinethmoid is a midline sesamoid bone or cartilage within the intermaxillary ligament that is unique to cypriniform fishes.¹⁰

(Figure 1. A simplified diagram of Devario fish. Numbers correspond to landmarks for measurements taken in a study. Credit: https://doi.org/10.1111/eff.12799)

Though there are at least five other Sri Lankan Devario species, D. malabaricus can be distinguished by their anteriorly bifurcated (forked) P stripe that originates at their forked caudal fin. Both sexes lack nuptial tubercles, however males have epidermal tubercles located on the anterior rays of the pectoral fin.²

(Figure 2. Live color patterns and specimen color patterns of D. malabaricus (orange dot) and D. micronema (green dot). Credit: https://doi.org/10.1111/eff.12799)

Geographic Distribution

The Malabar danio is a widespread, habitat generalist native to the lowest peneplains of both Sri Lanka and southern India.⁷ Note that at the time of description, present-day Kerala, India was known as Malabar. D. malabaricus is the only Sri Lankan Devario species also occurring in India. D. malabaricus occupies more habitat types and a broader range of environments than the Devario species endemic to Sri Lanka. Their ecological generalism may be linked to their greater sexual dimorphism as compared to the similar species D. micronema.³ They may reside in lowland flood plains, hill streams, and mountain torrents from elevations of sea level to approximately 1,300 m above sea level.³ Their temperature range lies from 18 °C to 25 °C.¹ D. malabaricus lives in various ecoclimatic zones including waters varying in turbidity, shade, and disturbance levels.³ This species can live in both lotic and lentic ecosystems. In Sri Lanka, D. malabaricus can be found in both dry zones and wet zones. Their wide geographic distribution appears to be a contributor to their relatively unrestricted gene flow, as they lack the phylogeographic structure observed in other Sri Lankan Devarios.⁸

[Figure 3. A phylogenetic tree depicts the evolutionary relationships between five Sri Lankan Devario species. A map locating Sri Lanka is displayed alongside. Credit: https://doi.org/10.1016/j.ympev.2020.106853]

Biology and Life-History

Malabar danios often form medium sized shoals close to the surface of the water column.² They feed on terrestrial insects and detritus.1 A study investigating temperature and hunting suggests that Malabar danios have an increased reaction distance and therefore an easier time searching for food in higher temperatures, even though the elevated temperatures do not lead to a significant increase in body speed.⁴ Though they can live in reservoirs and tanks, these fish are found to prefer flowing water.

Malabar danios are group spawners and egg scatterers.² They are oviparous, and spawn in shallow water after heavy rains among plants growing on the bottom. An adult will spawn around 200 light-orange, sticky eggs that will hatch in one to two days. The fry will be free-swimming after the fifth day. They do not exhibit parental care. The parents must be removed from aquaria to prevent them from eating the eggs, as this species exhibits egg cannibalism.

These fish are extremely difficult to identify as juveniles and can only be identified once mature.¹¹ Size and maturity go hand in hand for this species. Males of size 50 mm are said to reach first maturity and the size at first maturity is 40 mm for females. Fecundity ranges between 20 and 30 per gm body weight.¹¹ Malabar danios exhibit sexual dimorphism but retain similar body sizes.² Interestingly, Malabar danios release an alarm substance of 7-hydroxybiopterin when injured that alerts other Malabar danios to swim rapidly away when they detect the substance.⁶ This alarm reaction has also been observed in other cyprinid fish species.

Conservation Status

The IUCN Red List of Threatened Species listed D. malabaricus as Least Concern as of August 2019.² This organization has previously assessed this species as a species of Least Concern in 2009 and 2011, suggesting that D. malabaricus has a relatively stable overall population. It can be assumed this species is threatened by common issues plaguing other aquatic life in this region. Threats to D. malabaricus include anthropogenic habitat alteration, agricultural pollution, dams, indiscriminate fishing, invasive species, and climate change.²

Additionally, the Malabar danio is a popular aquarium fish. Exploitation for the aquarium trade may lead this species to decline in its native habitat. Captive breeding programs for the aquarium trade in places such as Singapore, Thailand, and Hong Kong have helped reduce the number of D. malabaricus taken from the wild, but it is unknown if the boosted prevalence of D. malabaricus in aquariums will harm wild populations in the future. There are no management or monitoring programs for this species as of 2019.²

See also

• List of freshwater aquarium fish species