Every species

Crossocheilus nigriloba is a cyprinid endemic to Borneo, known from the Kapuas, Belayan and Mahakam rivers in Indonesian Kalimantan. Rarely seen, it is among the near-identical congeners traded as 'Siamese algae-eater' or 'SAE' but is simple to identify: the lower caudal-fin lobe carries dark pigment suffused with red, which gave rise to the trade name 'penguin flying fox'. The lateral stripe breaks into blotches when the fish are sparring, stressed or sleeping.

Usually offered as the reticulated or fishnet flying fox, Crossocheilus reticulatus is a cyprinid from the Chao Phraya and Mekong basins. A silvery body, dark-edged scales and a dark caudal peduncle blotch set it apart from similar congeners. Patterning varies with collection locality, which led to several names now treated as synonyms. A fish of flowing streams, it is best kept in a group of six or more, since weaker individuals can be bullied in smaller numbers.

The gar characin, Ctenolucius hujeta, is a predatory pike characid from the Lake Maracaibo basin in Venezuela west to the Río Sinú in Colombia. Also traded as 'freshwater barracuda' and 'hujeta gar', it is surprisingly peaceful with anything too large to swallow. Juveniles school readily, and it is best kept in numbers of four or more with placid fishes that feed from the substrate. It is much the commoner of the two Ctenolucius in the hobby.

The grass carp, Ctenopharyngodon idella, is a large cyprinid native to the Amur River system in eastern Russia and northeastern China. Adults typically reach 800 to 1200 mm, making it a wholly unsuitable aquarium subject, though an albino form is traded. Widely introduced for aquaculture and weed control, it has caused serious damage to natural waters, and unwanted fish should never be released.

The leopard bushfish, Ctenopoma acutirostre, is an anabantoid from the middle Congo River basin, from Malebo Pool upstream to Boyoma Falls. Often sold as 'spotted climbing perch', it mimics leaves and other debris to stalk its prey, much like the unrelated South American leaf fish. Exceptionally hardy and long-lived, it can survive for over 15 years and makes an ideal species for the newcomer to 'oddballs'.

The tailspot ctenopoma, Ctenopoma kingsleyae, is an anabantoid with an enormous range, recorded from Mauritania and Senegal to Gabon and the DR Congo. One of the more aggressive members of the genus, it can be particularly nasty towards conspecifics and will eat small fish. It is named after the explorer Mary Kingsley, and there are reports of specimens surviving in aquaria for over 30 years.

The ocellated bushfish, Ctenopoma muriei, is one of the smallest members of its genus, recorded from Egypt and Sudan south to Tanzania and Zambia. It lives in sluggish or still waters such as pools, lagoons and swamps, many of them low in dissolved oxygen. Rarely seen in the trade, it will eat only the tiniest fish and suits an African community with Alestiid tetras, dwarf cichlids and small Mochokid catfish.

The mottled bushfish, Ctenopoma weeksii, is an anabantoid from the River Congo drainage in the Republic of Congo and Democratic Republic of Congo. It lives in sluggish, often hypoxic waters, usually among the thickest marginal vegetation. A predator of small fish but otherwise retiring, it can be kept in a group if all the fish are added at the same time.

The frail gourami, Ctenops nobilis, is an anabantoid from the Ganges and Brahmaputra systems in northeastern India, Bangladesh and Nepal. The only recognised member of its genus and a paternal mouthbrooder, it is usually regarded as very difficult to keep but is quite adaptable once acclimatised. It appears to react poorly to export and shipping, so imports are often in poor condition and prone to Oödinium. Adults can be openly hostile towards conspecifics.

The checkered pupfish, Cualac tessellatus, is a cyprinodontid endemic to a handful of springs in the Río Verde valley, San Luis Potosí, Mexico. Listed as Endangered by the IUCN, it lives in the shallow margins of crystal-clear, very hard spring-fed pools, including the Media Luna lagoon system. It is rarely available in the hobby, and captive breeding depends on very hard water, with the best results where chunks of gypsum rock are left to dissolve.

The featherfin cichlid, Cyathopharynx furcifer, is a maternal mouthbrooder endemic to Lake Tanganyika, where it lives over scattered rocks and sand. Highly sought after in the hobby but fairly delicate, it needs a lot of space and the highest water quality, and males develop full adult colour only at around 4 inches. Males dig spawning craters up to 60 cm across. The colour forms of the two Cyathopharynx species should not be kept together, as they can hybridise.

The beardless barb, Cyclocheilichthys apogon, is a cyprinid ranging from Myanmar to Vietnam and south via Peninsular Malaysia to Borneo and Sumatra. Also sold as 'skinhead barb', it lacks barbels and has a black blotch at the caudal-fin base plus rows of dark spots along the scale rows. It favours slower-moving or still water and grazes the biofilm on submerged roots and branches. Rarely imported in numbers, it most often arrives as bycatch.

Cyclocheilichthys armatus is a cyprinid ranging from the Mekong region through Thailand and Peninsular Malaysia to Borneo, Sumatra and Java. It forages from mid-water to the bottom of rivers in the dry season and is thought to migrate into flooded forest to breed. Rarely imported in numbers and most often arriving as bycatch, it makes a peaceful, unusual addition to larger aquaria in a group of at least six.

Cyclocheilichthys heteronema is a cyprinid ranging from Myanmar east to Vietnam and south to Peninsular Malaysia, Borneo and Sumatra. Its fimbriated barbels, extended downwards while it browses, are unique in the genus. It doesn't appear to be common in nature, with most records from Peninsular Malaysia, and it reaches the trade only as occasional bycatch. Very peaceful but retiring, it is easily outcompeted by boisterous tankmates.

Cyclocheilichthys janthochir is a cyprinid endemic to Borneo, known from West and Central Kalimantan in Indonesia. It inhabits black water streams and rivers associated with ancient forest peat swamps, where the water is very soft and acidic. Red markings in the dorsal and caudal fins plus a dark lateral stripe make it easy to identify. Specialised shops stock it from time to time, and it also turns up as bycatch among wild fish from Kalimantan.

Cyclocheilichthys lagleri is a cyprinid from the Chao Phraya river system in central Thailand and the lower Mekong basin in Thailand and Cambodia. It is observed mostly on low-altitude floodplains and may migrate into inundated areas to spawn. Lacking barbels entirely and with 20 circumpeduncular scales, it makes a peaceful, unusual addition to larger aquaria in a group of at least six.

Cyclocheilichthys repasson is a cyprinid with an enormous range, from the Mekong region and Myanmar through Peninsular Malaysia to Borneo and Sumatra. It grows to around 280 mm SL and favours slower-moving or still water, grazing the biofilm on submerged roots and branches. It is not often seen in the hobby. Most populations have a dark caudal peduncle spot, stripes formed by dark markings on the scales, and two pairs of barbels.

Cyclocheilos enoplos is a large cyprinid from the Mekong region and Thailand south through Peninsular Malaysia to Borneo, Sumatra and Java. Growing to around 750 mm SL, it is clearly unsuitable for aquaria and scarce to non-existent in the ornamental trade. In the Mekong it makes long seasonal migrations, and adults move upstream above Khone Falls in what appear to be spawning migrations.

Cynodon gibbus is a cynodontid from much of the Amazon basin, the middle and lower Orinoco, and the Rupununi River in Guyana. A pelagic fish of main river channels and larger tributaries, it grows to around 280 mm SL. It is rare in the trade but arguably more suitable for the home aquarium than some of its better-known relatives, given its size and relatively docile behaviour. Being easily dominated, it is best kept alone or with similarly sized, non-aggressive fishes.

The dogtooth cichlid, Cynotilapia afra, is a Mbuna endemic to Lake Malawi, found around the rocky shoreline. It is easily confused with some Pseudotropheus but has unicuspid teeth, and its black flank bars continue into the dorsal fin. The many colour forms should not be mixed, as they interbreed. Belligerent and very aggressive towards its own species, it is one of the hardier Mbuna and a good choice for the newcomer to these fish.