Anabas testudineus (BLOCH, 1792)

Climbing Perch, Kletterfisch (DE)

SynonymsTop ↑

Anthias testudineus Bloch, 1792; Perca scandens Daldorff, 1797; Amphiprion scansor Bloch & Schneider, 1801; Lutjanus testudo Lacepède, 1802; Anabas spinosus Gray, 1834; Anabas variegatus Bleeker, 1851; Anabas macrocephalus Bleeker, 1855; Anabas oligolepis Bleeker, 1855; Anabas microcephalus Bleeker, 1857; Anabas trifoliatus Kaup, 1860; Anabas elongatus Reuvens, 1895; Anabas testudineus kavaiya Deraniyagala, 1952; Anabas testudineus lacustris Das, 1966; Anabas testudineus ricei Das, 1966; Anabas testudineus riveri Das, 1966; Anabas tongtruongensis Nguyen, Ngô & Nguyen, 2015

Etymology

Anabas: from the Greek anabás (Gr. ἀναβάς), meaning ‘having gone up’, in reference to the ability of type species Anabas testudineus to move short distances over land.

testudineus: Latin term for ‘tortoise-like’, in reference to this species’ hard and solid skull structure.

Classification

Order: Perciformes Family: Anabantidae

Distribution

The type locality is given as “Japan” by Bloch, but this was in error and the species does not occur naturally there. It is however widely distributed in Pakistan, India, Bangladesh, Nepal, Bhutan (probable), Sri Lanka, Myanmar, Thailand, Cambodia, Laos, Vietnam, southern China, Malaysia, Indonesia, Brunei Darussalam and Singapore.

It is farmed commercially for food in several countries with non-native populations now established in the Philippines, Papua New Guinea, some Pacific islands close to Australia and possibly elsewhere.

Habitat

Inhabits the majority of drainage systems across its native range and has been recorded in many different habitat-types including swamps, marshes, lakes, canals, pools, small pits, rice paddies, puddles, oxbows, tributaries and main river channels. Though primarily a lowland, freshwater species it also occurs in brackish coastal environments in some areas.

During the wet season it often enters ephemeral flooded habitats where it may become trapped as waters recede. If necessary it’s able to travel across land for distances of several hundred metres provided it remains moist. These movements are not thought to be undertaken on a regular basis but are more likely related to extremes of competition, contamination or a lack of water literally giving the fish no other choice than to find more suitable habitat. Under extreme circumstances it’s even able to aestivate for several weeks by burying itself into moist ground.

Contrary to some accounts A. testudineus has never been recorded to hunt or forage while emerse nor is it capable of climbing trees due to its limited physiology. The latter rumour apparently originated towards the end of the 18th century when a specimen was found in a tree 5 feet off the ground but is now thought to have been transported there by a bird or other animal. When moving over land its movements are in fact somewhat slow and ungainly as it supports itself by splaying the pectoral fins and opercles, both of which feature thickened, specially-adapted spines, while forward momentum is provided via lateral movements of the caudal fin and posterior part of the body.

Maximum Standard Length

Officially 150 – 200 mm, but it appears that some forms may be fully-grown at 100 – 120 mm..

Aquarium SizeTop ↑

A tank with base dimensions of 100 cm x 45 cm is required, even for a single specimen, and a group of adults would need something much larger.

Maintenance

Ideally a soft, sandy substrate should be used though it is not essential. Additional furnishings are as much a case of personal taste as anything else although ideally plenty of cover should be provided. The most favoured set-ups tend to feature relatively dim lighting plus some chunks of driftwood, scattered roots/branches and a layer of floating vegetation such as Ceratopteris thalictroides or similar. Other plant species can also be added according to preference.

Although reports of this species ‘climbing’ are greatly exaggerated (see ‘habitat‘) use of a tightly-fitting cover is still essential since it is an accomplished jumper and also an obligate breather of atmospheric air (see ‘notes’) which should ideally be humid. Leaving a gap of 10 – 15 cm between water surface and cover should suffice. Although filtration must be efficient strong water flow should be avoided if possible.

Water Conditions

Temperature: 15 – 30 °C

pH: 5.5 – 8.0

Hardness: 36 – 447 ppm

Diet

Chiefly predatory though wild fish apparently feed on some vegetative matter including algae and rice grains as well as smaller fishes, invertebrates and molluscs. In the aquarium larger live and frozen foods such as earthworms or shellfish are taken and most specimens will also learn to accept dried alternatives, with pelleted products generally preferred to flake.

Behaviour and CompatibilityTop ↑

Unsuitable for the general community given its adult size and predatory nature. Much smaller fishes are likely to be eaten but suitably-sized, robust cyprinids, catfishes, cichlids and mastacembelids are normally ok provided sufficient space is available.

There exist mixed reports as to the degree of intraspecific aggression displayed by this species when maintained in captive groups. While some experiences appear to suggest it is belligerent and territorial others describe a relatively placid, even peaceful fish. The lack of clarity may be related to its confused taxonomic status in that several species are possibly being referred to under the same name (see ‘notes’), or perhaps different populations have evolved contrasting behavioural traits due to some ecological influence(s). Temperature may even play a part since many fish species are known to become more aggressive under warm conditions.

Sexual Dimorphism

Sexually active females are slightly larger and noticeably thicker-bodied than males, while males are darker in colouration and apparently develop tubercules on the pectoral fins when breeding. These observations relate to specimens from West Bengal state, northern India meaning they may not prove applicable to all populations.

Reproduction

One of the few anabantoids, alongside members of the genera Helostoma and Ctenopoma, not to exhibit parental care. It’s rarely-bred in aquaria without the aid of hormones but it is apparently possible with the fish becoming sexually mature at less than a year old and measuring 100 – 120 mm in length. When in spawning condition males develop a reddish hue to the body, particularly on the pectoral and ventral fins and a blackish, diamond-shaped marking appears on the caudal peduncle, Females display only a faint reddish colour while the caudal peduncle spot is oblong in shape and somewhat diffuse. Females also become rounded as they fill with eggs and exhibit a prominent bulge at the vent which is absent in males. it should be noted that this may not be true for all populations since it is based on observations of Indian fish.

In nature the eggs are deposited in open water at the onset of the rainy season with the male wrapping itself around the female and fertilising the eggs as they are laid. Around 200 eggs are released until during each embrace with each female capable of laying 5000-35,000 during a single spawning event. The eggs are not adhesive and rise to the surface where they float for approximately 24 hours before hatching. The emergent fry are about 2-3 mm long and free swimming within two days of hatching.

NotesTop ↑

This species isn’t especially popular in the aquarium trade but is undoubtedly interesting despite its lack of colour. In addition to its survival ability in the absence of water it’s also capable of producing audible sounds though the purpose of these has not been fully-studied. Naturally-occurring xanthic and albino forms have also been recorded.

There is considerable confusion as to the taxonomic status of the two species currently occupying this genus, with ichthyologists widely agreeing that there probably exists a number of additional taxa given the range of morphological differences exhibited by different populations plus their wide distribution. Some of these have been previously described as distinct species or subspecies but most are now considered synonymous with A. testudineus. The only other valid name at time of writing is A. cobojius which represents the form native to northern India and Nepal but even this should be treated with caution and we include everything under A. testudineus here.

The lack of clarity regarding the composition of the genus also leads to inevitable issues in terms of assessing conservation status and the IUCN currently classifies A. testudineus as ‘data deficient’ pending taxonomic review. A 2000 study which involved DNA analysis of six wild Thain populations in order to compare them with farmed specimens revealed all to be genetically distinct from one another while a taxonomic comparison between a form from Bangladesh and one introduced from Thailand for food revealed differences in some aspects of morphology, meristics and patterning.

Any comprehensive study of the species across its entire geographic range is likely to be complicated by the fact that artificial population mixing has already occurred in some places due to escapes from aquaculture projects. For example many of those produced by commercial farms in Bangladesh originate from Thailand which is somewhat inexplicable given the species occurs there naturally.

What is slightly more certain is the phylogenetic position of the genus within the suborder Anabantoidei where it almost certainly represents the sister group to the African anabantids i.e. members of Ctenopoma, Microctenopoma and Sandelia.

Like others in the suborder Anabantoidei this species possesses an accessory breathing organ known as the labyrinth. So-called due to its maze-like structure this organ allows the fish to breathe atmospheric air to a certain extent. It comprises paired suprabranchial organs which are formed from the expansion of the epíbranchial (upper) section of the first gill arch and housed in a chamber above the gills. It consists of many highly vascularised, folded flaps of skin the form of which greatly increases the available respiratory surface area. The structure of the organ varies in complexity between species tending to be more well-developed in those inhabiting particularly oxygen-deprived conditions.

A. testudineus has the largest suprabranchial organs and greatest-sized labyrinth apparatus relative to body mass of all anabantids, and is often said to be the most primitive member of the family. Unlike in other teleosts the opercular and subopercular bones are not fused into a single entity but joined by a thin, flexible membrane meaning the opercle is essentially hinged and can open very widely with the subopercular rotating both ventrally and laterally.

References

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