Oryzias eversi HERDER, HADIATY & NOLTE, 2012

Etymology

Oryzias: from the Greek ὄρυζα (oryza), meaning ‘rice’, in reference to the tendency of some members of the genus to inhabit rice paddy fields.

eversi: named for Hans-Georg Evers, who discovered this species.

Classification

Order: Beloniformes Family: Adrianichthyidae

Distribution

Type locality is ‘Salo Sadang drainage, stream close to village Tilanga, about 8 km south of Rantepao, 3°02.126’S, 119°53.232’E, Tana Toraja, South Sulawesi Province, Sulawesi, Indonesia’, and the species is currently known only from this single location.

Habitat

The type locality is a karst pool around 30-40 m in length, 10m in width and up to 4 m deep.

It contains still, transparent water, has a single inflow and outflow, is surrounded by rainforest and in September 2010 the water temperature was 21.5°C/70.7°F.

The habitat is used by locals as a bathing pool and sympatric species included a native Nomorhamphus sp. and introduced Poecilia reticulata with O. eversi males occurring singly and females in groups close to the vegetated margins.

Maximum Standard Length

35 – 40 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 75 ∗ 30 cm or more is recommended for a group.

Maintenance

This species presents no special requirements in terms of décor though it tends to be less colurful when maintained in a sparsely-decorated set-up.

It arguably looks best in a display inspired by its natural habitat which could consist of a sandy substrate, some water-worn tree roots and branches plus a few handfuls of leaf litter.

Planted aquaria are also suitable and may offer fry a more favourable chance of survival alongside the adults.

Water Conditions

Temperature: 18 – 24 °C

pH: 6.0 – 7.5

Hardness: 90 – 268 ppm

Diet

Unfussy but must be provided with foods of a suitable size.

A combination of crushed or small-grade, high quality dried foods plus live microworm, Artemia nauplii or similar appears to be ideal and adults have also been observed grazing from solid surfaces, so the natural diet may also contain an algal component.

Behaviour and CompatibilityTop ↑

Peaceful but doesn’t make an ideal addition to many communities due to its small size.

Should you wish to maintain it alongside other fishes other diminutive species comprise the best options, while freshwater shrimp of the genera Caridina and Neocaridina should also be suitable.

If the intention is breeding then it should ideally be maintained alone, and we don’t recommend keeping it with other Oryzias spp. due to the potential of hybridisation.

It’s non-aggressive towards conspecifics other than some sparring which occurs between courting males and tends to look most effective and behave more confidently in a group of 8 or more.

Sexual Dimorphism

Males possess elongate, filamentous rays in the dorsal and anal fins, relatively uniform body shape, and in nuptial individuals the dorsal, anal, pelvic and caudal fins plus part of the body become blackish.

The last ray of the pelvic-fin is also connected to the body by a membrane extending for half of its length.

In females the pelvic fins are greatly-extended and there is a deeply concave area, sometimes referred to as an ‘abdominal cavity’, between the pelvic and anal fins.

Females are more plainly-coloured than males in general, lack blackish nuptial colouration and the last pelvic-fin ray is not connected to the body by a membrane.

Reproduction

Utilises a strategy which has become known as ‘pelvic brooding’.

Spawning tends to occur in the early morning, with dominant males darkening in colouration and defending their space by driving away potential competitors, while approaching ripe females.

The eggs normally number 20-30 and are expelled as a single mass while being fertilised simultaneously, after which they continue to hang from the genital pore of the female via adhesive filaments.

Unlike in most Oryzias species however they are not brushed off after a few hours, rather the female carries them in the abdominal cavity using the elongate pelvic fins to keep them in place.

Egg-carrying females do not spawn again until hatching is complete and tend to conceal themselves among plants or other décor.

The incubation period is temperature dependant to an extent but typically 18-19 days.

While the adults tend to ignore the eggs they do predate free-swimming fry, though if the tank is densely-planted with fine-leaved or floating plants such as Cabomba, Ceratophyllum or Taxiphylum spp. some will usually survive.

Alternatively fry can be removed to a separate rearing container filled with water from the adults tank, or the female segregated from the rest of the adult group until hatching.

Once free-swimming the fry are able to accept microworm, Artemia nauplii, etc., immediately.

NotesTop ↑

This species is not common in the aquarium hobby but may become more widely-available in the future.

It can be distinguished from all congeners occurring on Sulawesi by the following combination of characters: possession of 17-18 (19) anal-fin rays; 10-12 dorsal-fin rays; 33–36 lateral scales; ½14 transverse scale rows at the dorsal-fin origin; 30–32 (33) total vertebrae; small eye (28.2–35.5 % HL); absence of dark bluish or steel blue body colouration, or brilliant red markings in both sexes; blackish colour pattern in nuptial males, including a blackish belly and posterior portion of body; 6–9 blackish lateral bars on each flank; a narrow black line on the light brown dorsal surface; i, 4/5, i principal caudal-fin rays;  pelvic brooding behaviour and associated morphology in females.

Members of the family Adrianichthyidae are often referred to collectively as ‘ricefishes’ and were traditionally considered to be members of the family Cyprinodontiformes and thus closely-related to toothcarps.

This misconception is sometimes still upheld despite the fact that Rosen and Parenti reclassified them within the cyprinodontiform sister group Beloniformes as long ago as 1981.

The best-known member of the family is the medaka or Japanese ricefish, Oryzias latipes, which has been widely used as a model organism in genomic and experimental biology for well over a century and was the first vertebrate animal to mate in space during the mid-1990s.

There are currently just two genera included in the family, Oryzias and Adrianichthys, with the historically-recognised groupings Xenopoecilus and Horaichthys having been synonymised with Oryzias by Parenti (2008).

Of the three species previously included in the paraphyletic Xenopoecilius, X. oophorus and X. poptae were moved into Adrianichthys with the third, X. sarasinorum currently recognised as Oryzias sarasinorum.

In addition the formerly monotypic Indian species Horaichthys setnai is currently classified as O. setnai.

References

1. Herder, F., R. K. Hadiaty and A. W. Nolte, 2012 - The Raffles Bulletin of Zoology 60(2): 467-476
   Pelvic-fin brooding in a new species of riverine ricefish (Atherinomorpha: Beloniformes: Adrianichthyidae) from Tana Toraja, Central Sulawesi, Indonesia.
2. Herder, F. and S. Chapuis, 2010 - The Raffles Bulletin of Zoology 58(2): 269-280
   Oryzias hadiatyae, a new species of ricefish (Atherinomorpha: Belonifornes: Adrianichthyidae) endemic to Lake Masapi, Central Sulawesi, Indonesia.
3. Magtoon, W., 2010 - Tropical Natural History 10(1): 107-129
   Oryzias songkhramensis, a new species of ricefish (Beloniformes; Adrianichthyidae) from northeast Thailand and central Laos.
4. Magtoon, W. and A. Termvidchakorn, 2009 - The Natural History Journal of Chulalongkorn University 9(1): 35-68
   A Revised Taxonomic Account of Ricefish Oryzias (Beloniformes; Adrianichthyidae), in Thailand, Indonesia and Japan.
5. Parenti L. R., 1981 - Bulletin of the American Museum of Natural History 168: 335-557
   A phylogenetic and biogeographic analysis of cyprinodontiform fishes (Teleostei, Atherinomorpha).
6. Parenti, L. R., 2008 - Zoological Journal of the Linnean Society 154(3): 494-610
   A phylogenetic analysis and taxonomic revision of ricefishes, Oryzias and relatives (Beloniformes, Adrianichthyidae).
7. Parenti, L. R. and R. K. Hadiaty, 2010 - Copeia 2010 (2): 268-273
   A new, remarkably colorful, small ricefish of the genus Oryzias (Beloniformes, Adrianichthyidae) from Sulawesi, Indonesia.
8. Roberts, T. R., 1998 - Ichthyological Research 45(3): 213-224
   Systematic observations on tropical Asian medakas or ricefishes of the genus Oryzias, with descriptions of four new species.
9. Rosen, D. E. and L. R. Parenti, 1981 - American Museum Novitates 2719: 1-25
   Relationships of Oryzias, and the groups of atherinomorph fishes.
10. Takehana, Y., K. Naruse K and M. Sakaizumi, 2005 - Molecular Phylogenetics and Evolution 36(2): 417-428
    Molecular phylogeny of the medaka fishes genus Oryzias (Beloniformes: Adrianichthyidae) based on nuclear and mitochondrial DNA sequences.
11. Uwa, H. and L. Parenti, 1988 - Japanese Journal of Ichthyology 35(2): 159-166
    Morphometric and meristic variation in ricefishes, genus Oryzias: a comparison with cytogenetic data.