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Golden Rainbow Shark 5cm (Epalzeorhynchos frenatum)

Epalzeorhynchos frenatum
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Family: Cyprinidae

Reportedly native to Thailand, Laos and Cambodia and was once widespread particularly in Thailand where it’s been recorded from the Mae Klong, Chao Phraya and Mekong river basins with occurences in the provinces of Chiang Mai, Phrae, Phitsanulok, Nakhon Sawan, Chainat, Kanchanaburi, Phra Nakhon Si Ayutthaya, Nakhon Ratchasima and Ubon Ratchathani.

Has most often been observed grazing sandy or rocky substrates in streams and rivers and is known to move into seasonally inundated floodplains or forested areas during the wet season. It is these migratory patterns that are thought to have been disrupted by human development.

Maximum Standard Length:
130 – 150mm.

Aquarium Size:
An aquarium with base measurements of 120 x 45cm should be the smallest considered for a single specimen, with larger quarters necessary for a group. It is advised to find a filter which has a water flow between 4-5 times the volume of your aquarium. 

Provided sufficient cover is available this species is relatively unfussy in terms of dcor, and should not harm softer-leaved plants. However it will thrive in a set-up designed to resemble a flowing river with a substrate of variably-sized rocks, gravel and some larger, water-worn boulders. This can be further furnished with driftwood roots and branches plus aquatic plants from genera such as Microsorum, Bolbitis or Anubias which can be grown attached to the decor. Bright lighting will promote the growth of algae and associated microorganisms, upon which the fish will graze. Like many fishes that naturally inhabit running water it’s quite intolerant to the accumulation of organic wastes and does best if there is a high level of dissolved oxygen and moderate water movement.

Water Conditions:
20 – 26°C
pH: Happy within the range 6.5 – 8.0 but a value close to neutral is usually recommended.
Hardness: 36 – 268ppm

Primarily an aufwuchs grazer feeding on algae, small crustaceans, insect larvae, etc., and for it to develop its best colours and condition it should be offered regular meals of small live and frozen foods such as bloodworm, Daphnia and Brine Shrimp along with good quality dried flakes, granules and fresh plant material. Shelled peas, cucumber, blanched zucchini, spinach and chopped fruit all make good additions to the menu. Once settled it will often ascend into midwater to feed and browse the biofilm that tends to form on rockwork and other solid surfaces.

Behaviour and Compatibility:
A slightly better choice for the community tank than Epalzeorhynchos bicolor but tankmates must still be chosen with care. While small specimens tend to hide away much of the time they become increasingly territorial as they grow and can display particularly high levels of aggression towards similar-looking species. Some individuals may be more belligerent than others and there exist reports of apparent alliances with other species such as Chromobotia macracanthus. We’re unsure if these behavioural differences are indicative of gender but at any rate loaches from the genera Chromobotia, Botia, Syncrossus and Yasuhikotakia do seem to be left in peace by Epalzeorhynchos species whereas congenerics and members of Crossocheilus, Garra and Gyrinocheilus, for example, tend to be attacked constantly. Please note that in terms of the loaches not all may be housed together and proper research is essential.

Other bottom-dwelling fishes including cichlids and most catfish are best avoided as they may too be picked on. For the upper levels choose robust, active, schooling cyprinids. Ideally the Epalzeorhynchos should be the final addition to the tank in order to avoid it claiming ownership of the entire space. This species probably lives a solitary lifestyle and in nature would probably have only come into contact with others of its own kind infrequently and during the spawning season. These instincts heighten as the fish get older and we therefore recommend it be kept singly in the majority of cases. In a very large tank with lots of cover a cohabitation attempt might be possible but each individual is likely to require a territory with a diameter of at least a metre.

Sexual Dimorphism:
Sexually mature females are noticeably thicker-bodied than males but it’s impossible to sex juveniles accurately. Males should also exhibit a dark marginal edge to the anal fin.

As far as we know it’s not been bred in private aquaria but large numbers are farmed for the ornamental trade with the aid of hormones.