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Origin: Brunei, Malaysia; Sarawak; in springs in Mulu National park.

Etymology: Macro=big, large; Stoma=mouth.

Synonyms:None.

First European import: Germany, 1984, by T. Schultz. First American import: 1980.

Description: See drawing on the stamp. Aquariumbred fish have fainter colors.

Care: Extremely difficult. Only specialists should try to keep the fish. Requires painfully pure and very soft water(90% RO), with a strong current, filtration over active peat. Large tanks are also advised, the fish can swim extremely fast, and have been known to kill themselves by swimming against the tank glass. Tanks should be covered extremely well, as Betta macrostoma is an excellent jumper, and is susceptible to cold air. Lot's of hideouts, especially floating plants, and very frequent large waterchanges. An UV filter is strongly recommended.

Temperature: 24-26 degrees.

Feeding: Varied live and frozen foods(krill) should be supplied. Carefull, don't use food that may be infected with diseases. In nature the animals mainly feed on live insects. Schultz(1999) described that sick foodfish, as well as red mosquitolarvae and tubifex caused Betta macrostoma to die.

Size: up to 11 cm, Schultz reports 9 cm in aquaria.

pH: 3.0-5.5

Breeding: If the fish can be kept alive, usually breeding will occur. The fish can be bred after 6 months, breeding occurs near the surface, and the female takes the initiative.

Sexual dimorphism:Males are much more colorfull.

Prices:Germany: 50-200€, USA 80-300$.

Additional: The fish is protected by the Sultan of Brunei, who likes the fish. It's prohibited to be in possession, to try to catch, or to keep the fish in a tank in Brunei. Please remember that they still have corporate punishment in that country, so do NOT try to smuggle the fish out of Brunei.

Schultz described how once infected fish refused to eat and died. Treating the fish with medication resulted in similar behaviour, besides that if a hole could be found to jump through all the fish in a tank with treatment would jump through the hole.

Picture references:Picture 1: Oliver Lucanus. Picture 2: Brunei stamp, www, public domain.

References:Baensch, H. A., Riehl, R.(1985): Aquarien Atlas II. Mergus Verlag, Melle, Germany.Oliver Lucanus; personal communication.

Schultz, T. (1999) : Sind Grossmaulkämpfer keine Aquarienfische?, DATZ, 4/99, pp 18-24.

If you are interested in this fish please join our anabantoid board

How to obtain these fish:
US and Canada: www.belowwater.com(Wholesale only, so ask your aquariumstore to order them for you)