Indostomus paradoxus

Described from Lake Indawgyi, with most of the type series collected at its northern end, near Nyaungbin, Kachin state, northern Myanmar, and subsequently recorded in tributaries of the Ayeyarwady/Irrawaddy River around the state capital of Myitkyina. More recently it's been found much further south near the town of Einme in the river's delta region, and thus appears to be considerably more widespread than previously thought.

Indostomus spp. tend to inhabit slow-moving or standing waters among submerged macrophytes, riparian vegetation or leaf litter. At the type locality of I. paradoxus the substrate was composed of black clay and water full of green algae, rotten and rotting vegetation (Prashad and Mukerji, 1929).

In March 2003 it was collected from a pool measuring around 20 m x 4 m with maximum depth about 1 m located close to Einme. The water was clear with a temperature of 29 °C84 °F, pH was 7.1, substrate composed of mud and there were dense growths of aquatic plants in the form of Nelumbo and Eichhornia spp.. Other fish species included Dario hysginon, Parasphaerichthys lineatus and Chaudhuria ritvae.

An aquarium with base dimensions of 40 ∗ 20 cm16 ∗ 8 in or more is sufficient.

Fares best in a well-planted set-up with a soft substrate although fine-grade gravel is acceptable. Driftwood roots or branches, floating plants and leaf litter can all be added to lend a more natural feel and further increase structural complexity while also serving to diffuse the light entering the tank, while lengths of suitably-sized plastic piping can also provide useful refuges and spawning sites. It naturally inhabits sluggish or still environments therefore filtration, or at least water flow, should not be very strong.

Chiefly a micropredator feeding on tiny aquatic crustaceans, worms, insect larvae and other zooplankton. In the aquarium it does not accept dried or frozen products as far as we know and must be offered small live foods such as Artemia nauplii, Daphnia, micro worm, etc., although grindal worm is normally refused for some reason. In mature, planted aquaria the naturally-occurring microfauna is likely to provide a useful additonal food source.

A poor competitor and will be preyed upon by larger fishes so it's best kept alone or with similarly-sized, placid species such as members of Boraras, Danionella or Dario. Though not gregarious in the sense of schooling/shoaling fishes it does seem to benefit from interaction with conspecifics and displays more interesting behaviour when maintained in numbers, therefore the purchase of no less than 4-6 individuals is recommended. Males are territorial towards rivals but do not damage each other.

Adult males possess broad, elongated pelvic fins with the outer rays curved inwards, while in females the pelvic fins are straight and more slender. Gravid female individuals typically display a rounded abdomen.

Has been bred in aquaria on numerous occasions. Spawning occurs in small caves or crevices including artificial alternatives such as small lengths of bamboo or plastic piping. Individual males select spawning sites and defend the area around these for a distance of a few cm in each direction. During the spawning period they take on an overall lighter, more reddish colouration, and exhibit a light brown stripe in the dorsal and anal fins. Females are courted via a display involving erect fins and quivering movements of the caudal region, taking place at the entrance to the spawning site. Receptive, ripe females take on a significantly paler colour pattern prior to and throughout spawning, and the protruding genital papilla is clearly visible. Eggs are most often deposited on the roof of the spawning site with both fish upside down during spawning. The overall process may involve several separate events with the female leaving the site briefly between each, and a typical clutch consists of 5-40 eggs. Post-spawning the female leaves the site and the male assumes sole responsibility for brood care, remaining in the tube or cave except for short periods of feeding. This behaviour is maintained until the fry are free-swimming and begin to disperse. In mature aquaria with an absence of predators it's possible that some fry may survive or they can be siphoned into a seperate container as and when spotted. The latter is no easy task, however, as newly-emergent fry are minute and if removed require microscopic food such as rotifers, Paramecium, etc. for the initial period.

This species is rare in the aquarium hobby though its name is often misapplied to the closely-related I. crocodilus. It can be told apart from congeners by the following characters: dorsal and anal fins without dark markings, with a light brown bar in breeding males; ventral surface light brown; throat white, occasionally with a few brown spots; ridges of head bones weakly serrated or not serrated, depending on the bone. In both I. crocodilus and I spinosus adult males possess dark bands in the dorsal and anal fins, these becoming more intense when breeding. I. crocodilus is otherwise similar to I. paradoxus, but in I. spinosus the ventral surface is coloured dark brown, throat marked with numerous brown spots, and the ridges of the head bones are strongly-serrated. The family Indostomidae currently contains just a single genus with three species of which I. paradoxus is the type. It was raised alongside both family and genus by Prashad and Mukerji (1929)[5], and remained the only member for 70 years until I. crocodilus and I. spinosus were described by Britz and Kottelat (1999)[3]. It's included in the order Gasterosteiformes which also includes the well-known stickleback family Gasterosteidae, and on description was considered most closely-related to pipefishes, seahorses, and sea dragons of the familes Solenostomidae and Syngnathidae. However the view of its placement has since changed several times with some wildly different suggestions. Banister (1970) studied the osteology of I. paradoxus and removed it from Gasterosteiformes, placing it in his new order Indostomiformes and recommending it be placed close to Gobiesociformes (cling fishes). Subsequent authors including Fraser (1972), Pietsch (1978), Patterson (1993), and Orr (1995) placed it variously close to, within, or unrelated to Gasterosteiformes. Britz and Johnson (2002)[4] demonstrated that Indostomus spp. are probably related to gasterosteoid gasterosteiforms via an analysis of I. paradoxus ontogeny. The two families display some notable similarities in structure and development of the body armour which are unique among fishes, but further study is still required to confirm the precise placement of Indostomus within the Gasterosteiformes.