Taxonomy & naming
Adrianichthys kruyti was described by Weber in 1913 from Lake Poso. The genus Adrianichthys holds the four large Poso buntingi, set apart from Oryzias by their size, their upturned jaws and their specialised reproduction. Kottelat's 1990 synopsis of the lake's buntingi is the standard modern reference for the genus.
Morphology
The species has a protruding, upturned lower jaw that gives the mouth a beak-like profile, which is why it is sometimes called the duckbill buntingi. Adults are much larger than any Oryzias; FishBase gives a maximum of 6.5 in TL.
Habitat
Endemic to Lake Poso, a deep tectonic lake in Central Sulawesi, Indonesia. FishBase describes it as a freshwater, pelagic fish and gives a pH range of 7.5 to 8.5 and a temperature range of 22 to 25 C for the lake. It lives at the surface and in open water rather than among weed beds.
Feeding
Diet has not been described for this species. The upturned mouth suits feeding at the surface.
Mating
Courtship and spawning behaviour have not been described for this species.
Breeding
FishBase notes that the eggs are carried, protected by the pelvic fins, until hatching rather than being scattered. Kottelat's work on the Poso buntingi describes a reproductive guild that differs from that of Oryzias. Clutch size and incubation time have not been published for A. kruyti.
In the aquarium
This species is not kept in aquaria. It is a lake endemic from a deep, large water body and has no record in the hobby.
Conservation
The IUCN Red List classes Adrianichthys kruyti as Critically Endangered, meaning it faces an extremely high risk of extinction in the wild. The species is confined to a single lake, where introduced fishes, fishing and habitat change affect the endemic buntingi.