Every species

Graham's soda cichlid, Alcolapia grahami, is endemic to Lake Magadi in Kenya, a shallow soda lake full of hot, alkaline springs. It lives around the spring inlets and lagoons of the shoreline in water of pH 9.5-10.5 at 32-43.5 °C, and excretes urea where most fish excrete ammonia. Exceptionally rare in the hobby, it can be acclimatised slowly to more normal conditions, but the pH should not drop below 8.0 or the temperature below 28 °C.

The Mozambique mouthbrooder, Oreochromis mossambicus, is a cichlid native to southeastern Africa and one of the most invasive fish in the world. Farmed for food across the globe, it now has escaped populations in over 90 countries. Known in the trade as the 'Mossie', it reaches 39 cm, breeds readily in large broods and is not recommended to most hobbyists. The brightly coloured forms seen in aquaria are selectively bred, and some are crosses with other Oreochromis.

The Nile tilapia, Oreochromis niloticus, is a cichlid with a very wide natural range in Africa, from Senegal east to Egypt and Uganda. Bred in huge numbers as a food fish, it has been introduced to over 70 other countries and is one of the most invasive fish species in the world. It reaches 60 cm, though usually around 35 cm, breeds readily, is very messy and does not make a good aquarium subject.

The Tanganyikan tilapia, Oreochromis tanganicae, is a large cichlid endemic to Lake Tanganyika, where it inhabits river mouths and shorelines. It is often seen in shoals in nature and appears to feed primarily on phytoplankton. Reaching 42 cm, it is not seen very often in the hobby.

Orthochromis stormsi is a cichlid from fast-moving, well-oxygenated stretches of the Congo River in the Democratic Republic of Congo. Its swimbladder is much reduced, so it is less likely to be swept away by the current, and in the aquarium it spends most of its time on the substrate, moving in a characteristic 'hopping' fashion. It was previously classified as Schwetzochromis stormsi and is still named as such by many sources.

The Asinua ricefish, Oryzias asinua, is known only from the Sungai Asinua in Southeast Sulawesi, Indonesia. The type series was collected along the shores and in small marginal pools on the adjacent floodplain. A member of the O. woworae species group, it differs from O. wolasi in that both sexes have orange-coloured olfactory epithelia, and it has a relatively slender body.

The Celebes ricefish, Oryzias celebensis, lives in rivers and streams of southwestern Sulawesi, Indonesia, with a further record from Timor. It is mostly found in slow-moving or standing waters, often where aquatic plants proliferate. Infrequently available in the hobby, it is exported on occasion and sometimes referred to as 'Celebes medaka'.

The Indian ricefish, Oryzias dancena, is widely distributed through eastern and southern India, Sri Lanka, Bangladesh and Myanmar. Mostly coastal but adaptable, it has been collected from strongly brackish mangrove swamps to acidic freshwater forest streams. It continues to be misidentified as O. melastigma, a name most recent workers consider invalid, or as O. javanicus, a valid but distinct taxon.

Oryzias eversi is a ricefish known only from a single karst pool in the Salo Sadang drainage, Tana Toraja, South Sulawesi, Indonesia. The pool holds still, transparent water and is surrounded by rainforest. Nuptial males develop a blackish belly and posterior body, and females show pelvic brooding behaviour. The species is not common in the aquarium hobby.

The Javanese ricefish, Oryzias javanicus, ranges through Peninsular Thailand, Malaysia, Singapore and Indonesia as far east as Lombok and Sulawesi. Typically found in coastal, normally brackish, streams, pools and mangrove swamps, it tolerates a wide salinity range and has also been recorded in fresh water. It is exported on occasion and sometimes referred to as the 'blue-eyed ricefish'.

The medaka, Oryzias latipes, is a ricefish from Japan, Korea, Taiwan, eastern China, Laos and Vietnam. Long used as a model organism in genomic and experimental biology, it was the first vertebrate animal to mate in space, in the mid-1990s. The ornamental 'golden' variant is more often seen than the natural form, and a transgenic 'glowing' form is illegal to buy, sell or own within the European Union.

Oryzias mekongensis, the Mekong ricefish, is endemic to the Mekong River system in northeastern Thailand, Laos and Cambodia. It reaches about 21 mm SL and is known only from fresh water, mainly clear water swamps, canals, ditches and ponds with dense fine-leaved plants. Males have bright orange-red marginal bands on the caudal-fin lobes, and it may be sold as the 'Mekong redfin lampeye killifish'.

The dwarf medaka, Oryzias minutillus, is a miniature ricefish from Thailand, with records from Myanmar, Cambodia and southern China. It lives only in fresh, normally standing waters such as shallow pools, ditches, rice paddies and clear water swamps. Adults reach just 17 mm SL. Traded occasionally, it is also known as the 'dwarf ricefish'.

Sarasin's buntingi, Oryzias sarasinorum, is a ricefish endemic to Lake Lindu in Lore Lindu National Park, Central Sulawesi, Indonesia. Also known as Sarasin's minnow, it is exceptionally rare both in nature and the aquarium hobby. It was formerly placed in Xenopoecilus, and a broad silvery lateral stripe and 70-75 lateral scales separate it from all other Oryzias.

Oryzias songkhramensis is a small ricefish known only from the Songkhram River basin in northeastern Thailand and the Mekong drainage in Laos. It lives only in fresh, normally standing water such as shallow pools, ditches, rice paddies and clear water swamps. Males have black and yellow or orange marginal bands on the caudal-fin lobes, and there is a black spot at the base of the pectoral fins. It resembles O. mekongensis, which has been available in the hobby.

The Wolasi ricefish, Oryzias wolasi, is known from four localities south of Kendari in Southeast Sulawesi, Indonesia. Discovered in 2009, it was referred to as O. sp. 'Kendari', O. sp. 'neon' or O. sp. 'Sulawesi' before description. A member of the O. woworae species group, it lives in karstic streams ranging from swift waterfalls to the remnant pools of an ephemeral river.

Daisy's ricefish, Oryzias woworae, is known only from a single stream on the island of Muna, Southeast Sulawesi, Indonesia. At 25-30 mm it is the most diminutive Oryzias known from Sulawesi. It caused something of a sensation when it first appeared in the trade shortly after description, and was collected schooling in a still pool of a karstic forest stream.

The elephant ear gourami, Osphronemus exodon, is a large gourami from Thailand, Laos and Cambodia. Its greatly enlarged teeth, with an extra set in concentric bands on the outer lips, stay visible when the mouth is closed and are used to pick fruit from overhanging branches. Reaching 60 cm, it inhabits still or slow-moving areas of large rivers and enters flooded forest in the rainy season.

The giant gourami, Osphronemus goramy, is a large gourami from Borneo, Java, Sumatra, Thailand, Indo-china and the Malay Peninsula. Reaching 70 cm and living for over 20 years, it is often sold as a juvenile with no information on its adult size. It is cultured for food on a large scale, a golden variety exists in aquaria, and dyed fish are produced by injecting colour under the skin.

The giant red tail gourami, Osphronemus laticlavius, is a large gourami from Indonesia and Malaysia, described to science in the early 1990s. Adults develop bright red fin edges with filamentous extensions and a body colour between blue-green and almost black. It reaches 50 cm and probably inhabits slow-moving rivers and other sluggish or stagnant water.