Indostomus crocodilus

Overview

The tiny Indostomus crocodilus comes from southern Thailand and northeastern Peninsular Malaysia. Males show dark brown to black bars in the dorsal and anal fins. Poor feeding competition and a need for minute live prey favor a quiet, mature planted aquarium over a general community.

Distribution & habitat

Records include Narathiwat and the Tapi basin in Surat Thani, Thailand, and neighboring Kelantan in Malaysia. A broader southern Thai range is possible, but the known sites do not establish occurrence in every river.

The type fish came from a blackwater stream in Toh Daeng peat-swamp forest, sheltering among submerged marginal roots and leaves in slow or still water. Tapi floodplain records also include stagnant habitats, such as an oxbow surrounded by freshwater scrub and swamp trees, with mud, fallen wood, and decomposing plants on the bottom.

Aquarium setup

Use dense planting over soft substrate or fine gravel. Roots, branches, floating plants, and leaves add hiding places and diffuse light. Suitably narrow plastic tubes can provide both refuges and spawning sites.

Keep current gentle. Its still- and slow-water habits do not suit continuous exposure to strong flow.

Diet & feeding

It primarily captures minute aquatic crustaceans, worms, insect larvae, and other zooplankton. Prepare tiny live foods such as Artemia nauplii, small Daphnia, and microworms. Existing husbandry experience reports rejection of dry and frozen products, with grindal worms also usually refused. Depending on a single worm culture while waiting for acceptance is therefore unreliable.

Natural microfauna in a mature planted tank may supplement feeding, but continue monitoring live-food provision and actual intake.

Behaviour & compatibility

Larger fishes can eat it, and it competes poorly at meals. Prefer a species aquarium or carefully chosen, similarly sized placid companions. It does not form a coordinated school, yet appears to benefit from interactions with its own kind; keep at least four to six.

Males defend areas against rivals but generally do not injure each other. Companions and dispersed shelters reveal a wider range of behavior than treating it as a strictly solitary fish.

Sexual dimorphism

Male pelvic fins are broad and elongated, with outer rays curving inward. Females have narrower, straighter pelvic fins and develop a rounded abdomen when carrying eggs. Dark dorsal and anal bars are also useful male markings.

Breeding

Aquarium breeding has succeeded repeatedly. Eggs are laid in small caves or crevices, including bamboo or plastic tubes. A male selects a site and defends several centimeters around it. During breeding his body becomes paler while dorsal and anal pigmentation intensifies; raised fins and tail quivering at the entrance form part of courtship.

A ready female becomes markedly paler before and during spawning, with a visible genital papilla. The pair often turns upside down to place eggs on the roof. A clutch can be deposited in several bouts with brief female departures, usually totaling five to forty eggs.

Afterward the female leaves and the male provides sole care, remaining inside except for short feeding excursions until fry swim freely and disperse. Some young may survive in a mature aquarium without predators. Alternatively, newly visible fry can be carefully siphoned to a rearing container.

Emerging fry are extremely small, making both transfer and first feeding difficult. Separate rearing requires microscopic foods such as rotifers and Paramecium, not an immediate move to the adult menu.

Notes

Compared with Indostomus paradoxus, male fin bars are darker. The underside is pale brown, the throat white or sparsely spotted, and head-bone serrations weak. Indostomus spinosus has a darker underside, more throat spotting, and stronger serrations. Slender body shape alone is insufficient for identification.

The group's systematic placement has been debated, with armor structure and development central to research. For keepers, accurate identity and a dependable supply of tiny live prey are the more immediate concerns.