Labyrinth Fish

Chocolate gourami
The chocolate gourami (Sphaerichthys osphromenoides) is a species of gourami native to the Malay Peninsula, Sumatra, and Borneo. Chocolate gouramis reach a length of 6 cm (2.4 in). These fish have a chocolate colour with golden bands running down their bodies.

Chocolate gourami

Live Bearer Fish

Guppies and mollies

Guppy

The guppy (Poecilia reticulata), also known as millionfish and rainbow fish, is one of the world's most widely distributed tropical fish, and one of the most popular freshwater aquarium fish species. It is a member of the Poeciliidae family and, like almost all American members of the family, is live-bearing. Guppies, whose natural range is in northeast South America, were introduced to many habitats and are now found all over the world. They are highly adaptable and thrive in many different environmental and ecological conditions. Male guppies, which are smaller than females, have ornamental caudal and dorsal fins, while females are duller in colour. Wild guppies generally feed on a variety of food sources, including benthic algae and aquatic insect larvae. Guppies are used as a model organism in the field of ecology, evolution, and behavioural studies.

Guppies exhibit sexual dimorphism. While wild-type females are grey in body color, males have splashes, spots, or stripes that can be any of a wide variety of colors. The size of guppies vary, but males are typically 1.5–3.5 cm (0.6–1.4 in) long, while females are 3–6 cm (1.2–2.4 in) long.

A variety of guppy strains are produced by breeders through selective breeding, characterized by different colours, patterns, shapes, and sizes of fins, such as snakeskin and grass varieties. Many domestic strains have morphological traits that are very distinct from the wild-type antecedents. Males and females of many domestic strains usually have larger body size and are much more lavishly ornamented than their wild-type antecedents.

Guppies have 23 pairs of chromosomes, including one pair of sex chromosomes, the same number as humans. The genes responsible for male guppies' ornamentations are Y-chromosome linked and are heritable.

Guppy

Endler's livebearer

Poecilia wingei, known to aquarists as the Black-Bar Endler or Endler's livebearer, in the genus Poecilia, is a small fish native to the Paria Peninsula in Venezuela. They are proficient breeders and often hybridize with guppies. These very colorful hybrids are the easiest to find being offered in pet-shops, typically under the name Endler's Guppy. 

Endler's livebearer

Black molly

Poecilia sphenops is a species of fish, of the genus Poecilia, known under the common name molly; to distinguish it from its congeners, it is sometimes called short-finned molly or common molly. They inhabit fresh water streams and coastal brackish and marine waters of Mexico. The wild-type fish are a dull silvery color, often sprinkled black all over. The common molly can produce fertile hybrids with many Poecilia species, most importantly the sailfin molly. The male black mollies generally tend to be mildly aggressive.

Mollies rank as one of the most popular feeder fish due to high growth rate, birth size, reproduction, and brood number.

Varieties:
Selective breeding over centuries has produced several color variations and different body shapes.
 

Short-Finned Molly or Common Molly: They inhabit fresh water streams and coastal brackish and marine waters of Mexico. The wild-type fish are a dull silvery color, often sprinkled black all over. The common molly can produce fertile hybrids with many Poecilia species, most importantly the sailfin molly. The wild form is in fact quite rarely kept, as it has a rather plain silvery coloration suffused with brown and green hues.
 

Black Molly or Midnight Molly: This variety actually originated from hybrids between Poecilia sphenops and the sailfin molly. Due to genomic recombination, F1 hybrids often display novel and bizarre fin shapes. It is a melanistic breed which are black all over. It is one of the most well-known aquarium fishes and nearly as easy to keep and prolific as guppies.
White Molly: A white colored molly.

Golden Molly: Nicknamed the "24 karat".

Balloon Molly: This fish has a deformed spine due to a genetic defect that gives it its appearance. Through Selective breeding it is now widely available. Balloon mollies can still reproduce and live a normal life comparable to that of other mollies, but it has garnered controversy due to the belief that its defect gives it a shortened lifespan and a susceptibility to health problems.

Lyretail: A breed with an altered caudal fin structure.

Dalmatian Molly: A silver colored breed with black speckles (in extensively marked specimens, they may appear black with silvery speckles).

Black molly

Sailfin molly

The sailfin molly, Poecilia latipinna, is a species of fish of the genus Poecilia. They inhabit fresh, brackish, and coastal waters from North Carolina to Texas and the Yucatán Peninsula of Mexico.

Sailfin molly

Dalmatian molly

Dalmatian molly

Lyretail Molly

Lyretail Molly

Platies and swordtails

Southern platy

The southern platyfish, common platy, or moonfish (Xiphophorus maculatus) is a species of freshwater fish in family Poecilidae of order Cyprinodontiformes. A live-bearer, it is closely related to the green swordtail (X. helleri) and can interbreed with it. It is native to an area of North and Central America stretching from Veracruz, Mexico, to northern Belize.

The southern platyfish grows to a maximum overall length of 6.0 centimetres (2.4 in). Sexual dimorphism is slight, the male’s caudal fin being more pointed. The anal fin of the male fish has evolved into a gonopodium, a stick-shaped organ used for reproduction. The female southern platyfish's anal fin is fan shaped. Wild varieties are drab in coloration, lacking the distinctive dark lateral line common to many Xiphophorus species.

X. maculatus prefers slow-moving waters of canals, ditches, and warm springs. Omnivorous, its diet includes both plants and small crustaceans, insects, and annelid worms.

Breeders have developed a multitude of color varieties (e.g. orange, red, yellow, red/black, and black/white) which are common aquarium fish for hobbyists.

The southern platyfish is commonly known simply as the platy (pl. platys or platies), from the fish’s original generic name, Platypoecilus.

Southern platy

Variable platy

The variatus platy (Xiphophorus variatus), also known as variable platyfish or variegated platy, is a species of freshwater fish in family Poecilidae of order Cyprinodontiformes. A live-bearer, it is native to southern Tamaulipas and northern Veracruz states in northeastern Mexico. It is a popular fish in the aquarium trade due to its prolific breeding, as are hybrids with other members of its genus, most notably the southern platyfish.

The variatus platy grows to a maximum overall length of 7.0 cm (2.8 in). In the wild, they are olive in colour with black marbling or spots on the side of the caudal peduncle. Large males show blackish blotches on the dorsal fin. Unlike some other members of the genus, X. variatus has no claw at the tip of the fifth anal fin ray. The fourth pectoral ray shows well-developed serrae (saw-like notches). They typically have 20 to 24 lateral scales, 10 to 12 dorsal rays and two rows of jaw teeth. Males exhibit a more pointed or "needle-like" anal fin whereas the female have a more triangular anal fin.

Variable platy

Green swordtail

The green swordtail (Xiphophorus hellerii) is a species of freshwater/brackish fish in family Poeciliidae of order Cyprinodontiformes. A live-bearer, it is closely related to the southern platyfish or ‘platy’ (X. maculatus) and can crossbreed with it. It is native to an area of North and Central America stretching from Veracruz, Mexico, to northwestern Honduras.

The male green swordtail grows to a maximum overall length of 14 centimetres (5.5 in) and the female to 16 centimetres (6.3 in). The name ‘swordtail’ is derived from the elongated lower lobe of the male’s caudal fin (tailfin). Sexual dimorphism is moderate, with the female being larger than the male, but lacking the ‘sword’. The wild form is olive green in color, with a red or brown lateral stripe and speckles on the dorsal and, sometimes, caudal fins. The male’s ‘sword’ is yellow, edged in black below. Captive breeding has produced many color varieties, including black, red, and many patterns thereof, for the aquarium hobby.

The green swordtail prefers swift-flowing, heavily-vegetated rivers and streams, but is also found in warm springs and canals. Omnivorous, its diet includes both plants and small crustaceans, insects, and annelid worms.

X. hellerii has become a nuisance pest as an introduced species in a number of countries. It has caused ecological damage because of its ability to rapidly reproduce in high numbers. Feral populations have established themselves in southern Africa, including Natal, Hawaii, Madagascar and eastern Transvaal in South Africa and Otjikoto Lake in Namibia. Significant populations have also established themselves along the east coast of Australia.

One of the most popular tropical aquarium fish, the green swordtail has been bred into various hybrid forms for the aquarium hobby due to its hardiness and suitability for community tanks.

It is often designated X. helleri (with one ‘i’), but authorities consider this an orthographic error and the spelling with two ‘i’s to be the valid specific epithet. It is named after Karl Bartholomaeus Heller, who collected the type specimen. Due to interbreeding with the southern platyfish or ‘platy’, most swordtails in aquariums are hybrids to some degree.

The males’ elongated caudal fins have been found to significantly affect their chances at mating. The presence of a well-endowed male spurs the maturity of females, while it inhibits the maturity of juvenile males in the vicinity of the well-endowed male.

Green swordtail

Other Livebearers, like Gambusia

Western mosquitofish

The western mosquitofish (Gambusia affinis) is a species of freshwater fish, also known commonly, if ambiguously, as simply mosquitofish or by its generic name, Gambusia, or by the common name gambezi. There is also an eastern mosquitofish (G. holbrooki).

Mosquitofish are small in comparison to many other freshwater fish, with females reaching an overall length of 7 cm (2.8 in) and males at a length of 4 cm (1.6 in). The female can be distinguished from the male by her larger size and a gravid spot at the posterior of her abdomen. The name "mosquitofish" was given because the diet of this fish sometimes consists of large numbers of mosquito larvae, relative to body size. Gambusia typically eat zooplankton, beetles, mayflies, caddisflies, mites, and other invertebrates; mosquito larvae make up only a small portion of their diet.

Mosquitofish were introduced directly into ecosystems in many parts of the world as a biocontrol to lower mosquito populations which in turn negatively affected many other species in each distinct bioregion. Mosquitofish in Australia are classified as a noxious pest and may have exacerbated the mosquito problem in many areas by outcompeting native invertebrate predators of mosquito larvae. Several counties in California distribute mosquitofish at no charge to residents with manmade fish ponds and pools as part of their mosquito abatement programs. The fish are made available to residents only and are intended to be used solely on their own property, not introduced into natural habitat. On 24 February 2014, Chennai Corporation in India introduced western mosquitofish in 660 ponds to control the mosquito population in freshwater bodies.

Fertilization is internal; the male secretes milt into the genital aperture of the female through his gonopodium. Within 16 to 28 days after mating, the female gives birth to about 60 young. The males reach sexual maturity within 43 to 62 days. The females, if born early in the reproductive season, reach sexual maturity within 21 to 28 days; females born later in the season reach sexual maturity in six to seven months.

Western mosquitofish

Eastern mosquitofish

The eastern mosquitofish (Gambusia holbrooki) is a species of freshwater fish, closely related to the western mosquitofish, Gambusia affinis. It is a member of the family Poeciliidae of order Cyprinodontiformes. The eastern mosquitofish is native to the eastern and southern United States from Florida to Delaware and inland to Alabama and Tennessee, while the western mosquitofish has a larger distribution throughout the United States.

The Eastern mosquitofish is a small, light-colored fish with semitransparent fins. The females usually have a black stripe near their eye area and light spots can be seen on the caudal and dorsal fins of both sexes. Due to its similar size, shape, and reproductive habits, it can easily be mistaken for a guppy. Generally, males reach 1.5 in (3.8 cm) and females 2.5 in (6.4 cm). These fish are a livebearer species, and as such, the females are larger and more rounded than the males. Pregnant females are also easily recognizable by their gravid spot; a darker area on their bellies where they hold the fry.

Mesquitofish may have a melanistic color pattern with black spots, resembling a dalmatian. This is sometimes miss identified as another species.

In its native range, Eastern mosquitofish may be confused with the Western Mosquitofish (Gambusia affinis) or the sailfin molly (Poecilia latipinna).

In eastern Australia, the female and juvenile local Pacific blue-eye (Pseudomugil signifer) are similar in appearance but have a forked tail fin.

Eastern mosquitofish

Celebes half beak

Celebes half beak

Cuban lima

Cuban lima

Tangunyika pearl killifish

Tangunyika pearl killifish

Knife livebearer

Knife livebearer

Least killifish

Heterandria formosa (known as the least killifish, mosqu or midget livebearer) is a species of livebearing fish within the family Poeciliidae. This is the same family that includes familiar aquarium fishes such as guppies and mollies. H. formosa is not as commonly kept in aquaria as these species. H. formosa is one of the smallest fish in the world (7th smallest as of 1991), and is the smallest fish found in North America. Despite the common name "least killifish", it belongs to the family Poeciliidae and not to one of the killifish

Heterandria formosa is one of the smallest fish and smallest vertebrates known to science. Males grow to about 2 centimeters (0.8 inches), while females grow a little larger, to about 3 centimeters (1.2 inches).

The fish is generally an olive color, with a dark horizontal stripe through the center of the body. There is also a dark spot on the dorsal fin and females also have a dark spot on their anal fin. Like most poeciliids, males' anal fins are modified into a gonopodium that is used for impregnating females during mating.

Least killifish

Loaches and Related Cypriniformes Fish

Loaches

Bengal loach

The Bengal loach, or queen loach (Botia dario) is a species of fish in the loach family Botiidae found in the Brahmaputra and Ganges basins in Bangladesh, Bhutan and north India. The species is overall common in widespread.

In Bangladesh, these fish are threatened by pesticide used in the cultivation of rice. Since 1997, the Bangladesh government has enforced strict penalties against polluters, with specific rules about the pollution of streams and waterways, so at least some preservation work is afoot.

In Bangladesh, B. dario can be found in the creeks and streams of the northern and eastern regions of the country (bordering India and Myanmar, respectively). The fish most likely populates the streams that supply the Bengal section of the Ganges river. B. dario is also reported in Bhutan, but only in the Gaylegphug river, which eventually drains into the far north of Bangladesh.

Bengal loach

Blue Botia

The blue botia, Yasuhikotakia modesta, is a tropical freshwater fish of the family Botiidae. It is native to large rivers in Thailand, Laos, Cambodia, and Vietnam. The blue botia is a widely available fish in the aquarium trade and can be purchased globally. Other common names for this fish are red-finned loach, redtail botia, and colored botia.

The blue botia has a long, compact body and arched back similar to many other members of the Botiidae family including clown and yoyo loaches. Wild specimens have been found up to 25 centimetres (9.8 in) but those in captivity rarely grow larger than 18 centimetres (7.1 in). The body is bluish-gray and the fins are red, orange, and in rare instances yellow. Immature specimens sometimes have a greenish tint to their bodies. Good health is indicated by bright coloration.

Blue Botia

Burmese border loach

The Burmese Border loach, angelicus loach or polka dot loach, Botia kubotai, is a recently described species that has quickly become a popular tropical fish for freshwater aquariums. In 2002, fish collectors working in western Thailand began to expand their search into Myanmar (Burma) area from the Three Pagodas Pass Thai-Myanmar border to look for new fish for the aquarium trade. This is one of several species discovered and explains the origin of the fish's common name: Burmese Border Loach. Its specific epithet honors Katsuma Kubota of an aquarium export company in Thailand who first purchased the catch and sent them out for identification.

Burmese border loach

Clown loach

The clown loach (also tiger botia), Chromobotia macracanthus, is a tropical freshwater fish belonging to the botiid loach family. It is the sole member of the Chromobotia genus. It originates in inland waters in Indonesia on the islands of Sumatra and Borneo. It is a popular fish in the freshwater aquarium trade and is sold worldwide.

Information about the maximum size of the clown loach varies, with some estimates ranging up to 40–50 cm (16–20 in), and with typical adult sizes ranging from 15–20 cm (5.9–7.9 in). The fish's body is long and laterally compressed, with an arched dorsal surface and a flat ventral surface. Its head is relatively large and its mouth faces downward with thick, fleshy lips, and four pairs of barbels. The barbels on the lower jaw are small and difficult to see. Clown loaches can make clicking sounds when they are happy, being territorial (used as a type of weapon/warning) or mating. This sound is produced by the grinding of their pharyngeal teeth.

The body is whitish-orange to reddish-orange, with three thick, black, triangular, vertical bands. The anterior band runs from the top of the head and through the eye, the medial band lies between the head and the dorsal fin, and wraps around to the ventral surface, and the posterior band covers almost all of the caudal peduncle and extends to the anal fin. There is some regional color variation within the species; the pelvic fins on fish from Borneo are reddish orange and black, while the pelvic fins on fish from Sumatra are entirely reddish orange. The fish is sexually dimorphic, with females being slightly plumper than males. In addition, the tips of the tail on the male curve inwards slightly, whereas the females have straight tips. The fish has a movable spine that lies in a groove below the eye, which may be extended as a defense mechanism. The spine may cause a painful wound, but is not venomous. It also may be used as a predation tool as it is set close to the mouth.

Clown loach

Dwarf loach

The dwarf loach, ladderback loach, pygmy loach, chain loach or chain botia, (Ambastaia sidthimunki) is freshwater fish belonging to the Botiidae family. It is frequently seen in the aquarium trade. This endangered species is endemic to the Mae Klong basin (including Khwae Noi River) in Thailand, and the Ataran River on the Thai-Myanmar border. Records from the Mekong basin are misidentifications of the very similar and closely related A. nigrolineata.

Dwarf loach

Dojo loach, weather loach

The pond loach, dojo loach, or oriental/Japanese weather loach (Misgurnus anguillicaudatus), is a freshwater fish in the loach family Cobitidae. They are native to East Asia but are also popular as an aquarium fish and introduced elsewhere in Asia and to Europe and North America. The alternate name weather loach is shared with several other Cobitidae, including the other members of the genus Misgurnus and the spotted weather loach (Cobitis taenia, commonly known as spined loach). This term comes from their ability to detect changes in barometric pressure and react with frantic swimming or standing on end. This is because before a storm the barometric pressure changes, and this is known to make these fish more active. The pond loach also comes in a variety of colors, such as pink, orange, albino and gray.

Like many other loaches, pond loaches are slender and eel-like. They can vary in colour from yellow to olive green, to a common light brown or grey with lighter undersides. The mouth of the loach is surrounded by three sets of barbels. It uses them to sift through silt or pebbles to find food. It also uses them to dig under gravel and sand to conceal itself out of nervousness or defence unlike the other loaches who use the spines beneath the eyes.

They can grow up to 12 inches (30.5 cm) long. The fish are bottom-dwelling scavengers, feeding mainly on organic material such as algae. Pond loaches are omnivorous and may also feed on tubifex worms and other small aquatic organisms. By producing a layer of mucus to keep themselves damp they can survive short periods of desiccation. They are very hardy fish that can live in poor quality water.

Dojo loach, weather loach

Horseface loach

The horseface loach or horsehead loach (Acantopsis choirorhynchos) is a freshwater and brackish fish in the loach family (Cobitidae). This bottom-dwelling fish is native to the swift, clear streams and rivers of mainland and archipelagic Southeast Asia, from India to Indonesia through the Chao Phraya and Mekong river basins. It can also be found in flooded fields. A very similar species is the unofficially named longnose loach, Acantopsis octoactinotos, from which the horseface can be distinguished by the latter's down-turned (horse-like) nose. Additionally, the horseface loach buries itself in the bottom substratum (if silt or fine sand); the longnose loach does not. The horseface loach is fast moving; the longnose is rather slow. However, the longnose is more aggressive, regularly feeding on juvenile fishes. The horseface loach's native substrate is one of sand or gravel, wherein it will characteristically burrow itself. These loaches spend much of their time buried in the substrate, leaving only their eyes uncovered. Due to this incessant burrowing, any live plants should be potted to avoid uprooting. The use of floating plants is recommended, as these loaches prefer subdued lighting. Horseface loaches are not picky eaters, but live food (such as tubifex) is relished. The horseface loach is most active at night and mostly keeps to itself. It attains a maximum size of 30 centimetres (12 in) in length, but is considered mature from 6 centimetres (2.4 in). As of 1997, it had not been bred in captivity. It was first imported into Europe in 1929 by Edmund Riechers of Hamburg, Germany.

Horseface loach

Kuhli loach, coolie loach

The kuhli loach (Pangio kuhlii) is a small eel-like freshwater fish belonging to the loach family (Cobitidae). They originate from Indonesia and the Malay Peninsula. This snake-like creature is very slender and nocturnal. In an aquarium, the kuhli loach can be very reclusive and, when startled, will dart underneath tank ornaments or bury itself, if a fine gravel or sandy substrate is present. The kuhli loach is an eel-shaped fish with slightly compressed sides, four pairs of barbels around the mouth, and very small fins. The dorsal fin starts behind the middle of the body, and the anal fin well behind this. The eyes are covered with a transparent skin. The body has 10 to 15 dark brown to black vertical bars, and the gaps between them are salmon pink to yellow with a light underside. When the fish is not actively breeding, distinctions between males and females are not readily apparent. However, close observation will reveal that males have more a muscular upper/dorsal cross-section and their pectoral fins tend to be larger, more paddle-shaped, and often have some pigment in them. When breeding, the females often become larger than the male and their greenish ovaries can be seen through the skin before spawning. Spawning is not easy, but when it occurs a few hundred greenish eggs are laid among the roots of floating plants. Kuhli loaches reach maturity at 2 ¾ inches (7 cm) and have a maximum length of 4 inches (10 cm). This fish can live for up to about 10 years.

Kuhli loach, coolie loach

Longnose loach

Acantopsis octoactinotos or the Long-nosed loach is a freshwater fish from Indonesia, commonly found in aquariums. Acantopsis octoactinotos has a long straight snout, unlike the similar Horseface loach (Acantopsis choirorhynchus), in which the snout has a down-turned shape. The Long-nosed loach reaches 4.5 inches (110 mm) in length, males typically being smaller and slenderer than females.

Longnose loach

Skunk loach

The skunk loach, skunk botia or Hora's loach (Yasuhikotakia morleti; syn. Botia morleti, Botia horae) is a species of botiid loach found in the Mekong River basin in Indochina, as well as the Chao Phraya and Mae Klong basins in Thailand. The maximum size is 10 cm (4 in) and it occurs in water with parameters 26 - 30 ° C (79 to 86 ° F) temperature, pH 6.0 to 8.0, hardness 5.0 to 12.0. It feeds on live crustaceans, insects, snails and other invertebrates.

Skunk loach

Yoyo loach

The yoyo loach, Almora loach or Pakistani loach (Botia almorhae) is a freshwater fish belonging to the loach family Botiidae. It originates in the slow-running and still waters of the Ganges basin in northern India and possibly Nepal. Despite the alternative common name Pakistani loach, the true B. almorhae is not known from Pakistan (the species in this country is B. birdi).

It may attain a length of 14–16 cm (5.5–6.3 in), and is named for its dark and pale patterns, which often can be seen to spell "yoyo" (especially in smaller/younger specimens), hence the common name yoyo loach. The final common name, Almora loach, refers to Almora in Uttarakhand, India. Specimens labelled as B. almorhae are commonly found in the aquarium trade, but most (if not all) of these appear to be the closely related B. lohachata, two possibly undescribed species popularly referred to as B. sp. "Kosi" and B. sp. "Teesta", or hybrids.

Yoyo loach

Zebra loach

The zebra loach (Botia striata) is a freshwater loach native to rivers and streams in the Western Ghats of India. The maximum size is about 9 cm (3.5 in). It lives in tropical climate with temperature range of 21–26 °C (70–79 °F), and prefers water with 6.0 to 7.5 pH.

Zebra loaches are peaceful fish suitable to community aquarium tanks. However, being bottom feeders, they may show some aggression against other smaller bottom feeders. Therefore, small corydoras are not suitable tankmates. They should be kept in groups of at least five. Any fewer and they will become stressed. They require some caves in which to hide during most of daylight. B. striata will accept a wide variety of fish foods, including live food such as blackworms, snails and small shrimps, and most commercial brands of sinking fish foods.

This species is shy, and will spend much of its time hiding. Also rarely, during times of stress it has been seen to attack smaller fish such as tetras.

According to the IUCN, the zebra loach is currently endangered in the wild due to habitat alteration combined with a small native range. Aquarists interested in keeping zebra loach specimens are strongly advised to investigate the source of locally available fishes, and to only purchase those known to be captive-bred. Home aquarium breeding is unknown, but the species is bred on a commercial basis with the use of hormones.

Zebra loach

Other related cypriniformes

Chinese high fin banded shark

The Chinese high fin banded shark (Myxocyprinus asiaticus) is a popular freshwater aquarium fish that belongs to the Catostomidae family. It grows to about 1.35 m (4 ft 5 in) long and is unsuitable for most home aquariums.

In addition to Chinese high fin banded shark, it is also known under many other common names, including Chinese banded shark, Chinese sailfin sucker, high fin (also spelled hi-fin) banded loach, high fin loach, Chinese high fin sucker, sailfin sucker, topsail sucker, Asian sucker, Chinese sucker, wimple carp, wimple, freshwater batfish, Hilsa herring, rough fish, Chinese or Asian zebra high fin shark, Chinese or Asian zebra high fin sucker, Chinese emperor, Siamese sucker, Chinese banded shark, and Entsuyui in Japanese. Despite its common names, it bears no relation to real sharks except that they are both fish.

It has declined drastically due to pollution, dams (preventing its natural breeding migration), overfishing, introduced species and collection for the aquarium trade. As a consequence it has been placed on the Chinese list of endangered species and is a state protected species.

Young Chinese high fin banded sharks normally possess brown bodies bearing three dark-colored slanting bands. During the breeding season, adult males are distinguished from adult females by their red coloration. Adult females are of dark purple color with a broad and vertical reddish area along the body. Juveniles of the Chinese high fin banded sharks are also characterized by high and triangular dorsal finnage that extends up to the rear of the anal fin. The adult appearance is far less distinctive, as they are elongate in shape without the very high dorsal fin. The thick and fleshy lips bear small papillae without barbels. They have a single row of pharyngeal teeth that have comb-like arrangements.

Through adulthood, Chinese high fin banded sharks become darker in appearance. The characteristic pale bands found in young specimens disappear at a length of 30–36 cm (12–14 in), and the species has been referred to as an "ugly duckling in reverse". The maximum size reached by this fish is 1.35 m (4 ft 5 in) in length and 40 kg (88 lb) in weight.

Chinese high fin banded shark

Chinese hillstream loach

Beaufortia kweichowensis is a species of gastromyzontid loach native to rivers in China. The common names for this popular aquarium species are Chinese hillstream loach, Hong Kong pleco, butterfly hillstream loach, and Chinese sucker fish.

Chinese hillstream loach

Neotropical electric fish

The Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found exclusively in fresh water, these mostly nocturnal fish are capable of producing electric fields for navigation, communication, and, in the case of the electric eel (Electrophorus electricus), attack and defense. A few species are familiar to the aquarium trade, such as the black ghost knifefish (Apteronotus albifrons), the glass knifefish (Eigenmannia virescens), and the banded knifefish (Gymnotus carapo).

Aside from the electric eel (Electrophorus electricus), Gymnotiformes are slender fish with narrow bodies and tapering tails, hence the common name of "knifefishes". They have neither pelvic fins nor dorsal fins, but do possess greatly elongated anal fins that stretch along almost the entire underside of their bodies. The fish swim by rippling this fin, keeping their bodies rigid. This means of propulsion allows them to move backwards as easily as they move forward.

The caudal fin is absent, or in the apteronotids, greatly reduced. The gill opening is restricted. The anal opening is under the head or the pectoral fins.

These fish possess electric organs that allow them to produce electricity. In most gymnotiforms, the electric organs are derived from muscle cells. However, adult apteronotids are one exception, as theirs are derived from nerve cells (spinal electromotor neurons). In gymnotiforms, the electric organ discharge may be continuous or pulsed. If continuous, it is generated day and night throughout the entire life of the individual. Certain aspects of the electric signal are unique to each species, especially a combination of the pulse waveform, duration, amplitude, phase and frequency.

The electric organs of most Gymnotiformes produce tiny discharges of just a few millivolts, far too weak to cause any harm to other fish. Instead, they are used to help navigate the environment, including locating the bottom-dwelling invertebrates that compose their diets. They may also be used to send signals between fish of the same species. In addition to this low-level field, the electric eel also has the capability to produce much more powerful discharges to stun prey.

Black ghost knifefish

The black ghost knifefish (Apteronotus albifrons) is a tropical fish belong to the ghost knifefish family (Apteronotidae). They originate in freshwater habitats in South America where ranging from Venezuela to the Paraguay–Paraná River, including the Amazon Basin. They are popular in aquaria. The fish is all black except for two white rings on its tail, and a white blaze on its nose, which can occasionally extend into a stripe down its back. It moves mainly by undulating a long fin on its underside. It will grow to a maximum length of 50 cm (20 in). It does not have scales.

Black ghost knife fish are nocturnal. They are a weakly electric fish which use an electric organ and receptors distributed over the length of their body in order to locate insect larvae.

Black ghost knifefish with its underside pointing towards the camera

The black ghost knifefish natively lives in fast moving, sandy bottom creeks in a tropical climate. South American natives believe that the ghosts of the departed take up residence in these fish, hence the name.

The black ghost knifefish is a weakly electric fish as a result of the electromotor and electrosensory systems it possesses. While some fish can only receive electric signals, the black ghost knifefish can both produce and sense the electrical impulses. Electrogenesis occurs when a specialized electric organ found in the tail of the fish generates electrical signals, which are thus called electric organ discharges (EODs). Then, for these EODs to be sensed by the fish, electroreception occurs when groups of sensory cells embedded in the skin, known as electroreceptor organs, detect the electrical change. The EODs are used for two major purposes: electrolocation and communication.

The kind of EOD produced can be used to distinguish between two types of weakly electric fish: the pulse-type and the wave-type. The black ghost knifefish are considered to be the latter type, because they can continuously generate EODs in small intervals. Wave-type EODs have a narrow power spectra, and can be heard as a tonal sound, where the discharge rate establishes the fundamental frequency. By emitting its own continuous sinusoidal train of EODs, the fish can determine the presence of nearby objects by sensing perturbations in timing and amplitude of electric fields, an ability known as active electrolocation. The particular organs used to sense the self-generated high-frequency EODs are tuberous electroreceptor organs. On the other hand, when low-frequency electric fields are generated by external sources instead of the fish itself, a different class of electroreceptor organs is used for this passive electrolocation, called ampullary organs. Therefore, the black ghost knifefish uses an active and a passive electrosystem, each with its own corresponding receptor organs. The fish can also use a mechanosensory lateral line system, which detects water disturbances created by the motion of the fish's body. As nocturnal hunters, the fish can rely on all three systems to navigate through dark environments and detect their prey.

Each species has a characteristic EOD baseline frequency range, which varies with sex and age within the species, as well. The baseline frequency is maintained to be almost constant at stable temperature, but will usually be changed due to the presence of others of the same species. Such changes in frequency relevant to social interaction are called frequency modulations (FMs). The role these FMs have in communication is significant, as black ghost knifefish have developed jamming avoidance responses, which are behavioral responses that avoid the overlapping of EOD frequencies between conspecific individuals to prevent sensory confusion. Moreover, a study was conducted that focused on sexual dimorphism in electrocommunication signals. Female black ghost knifefish generate EODs at a higher frequency than the males, an FM which can be used for gender recognition. A study found the subdominant black ghost knifefish exhibited noticeable gradual frequency rises (GFRs) in their EODs whereas the dominant fish did not, supporting the researchers' hypothesis that GFRs during communication are indicative of submissive signals.

Elephant nose

Peters' elephant-nose fish (Gnathonemus petersii; syn. Gnathonemus brevicaudatus Pellegrin, 1919, Mormyrus petersii Günther, 1862) is an African freshwater elephantfish in the genus Gnathonemus. Other names in English include elephantnose fish, long-nosed elephant fish, and Ubangi mormyrid, after the Ubangi River. As the Latin name petersii confirms it is named after someone called "Peters" (probably Wilhelm Peters), although the apostrophe is often misplaced and the common name given as "Peter's elephantnose fish". It uses electrolocation to find prey, and has the largest brain-to-body oxygen use ratio of all known vertebrates (around 0.6).

Peters' elephantnose fish are native to the rivers of West and Central Africa, in particular the lower Niger River basin, the Ogun River basin and in the upper Chari River. It prefers muddy, slowly moving rivers and pools with cover such as submerged branches. It is a dark brown to black in colour, laterally compressed (averaging 23–25 cm), with a rear dorsal fin and anal fin of the same length. Its caudal or tail fin is forked. It has two stripes on its lower pendicular. Its most striking feature, as its names suggest, is a trunk-like protrusion on the head. This is not actually a nose, but a sensitive extension of the mouth, that it uses for self-defense, communication, navigation, and finding worms and insects to eat. This organ is covered in electroreceptors, as is much of the rest of its body. The elephantnose fish has poor eyesight and uses a weak electric field, which it generates with specialized cells called electrocytes, which evolved from muscle cells, to find food, to navigate in dark or turbid waters, and to find a mate. Peters' elephantnose fish live to about 6–10 years, but there are reports of them living even longer.

Electric eel

The electric eel (Electrophorus electricus) is an electric fish, and the only species in that genus. Despite the name, it is not an eel, but rather a knifefish.

The electric eel has three pairs of abdominal organs that produce electricity: the main organ, the Hunter's organ, and the Sach's organ. These organs make up four-fifths of its body, and give the electric eel the ability to generate two types of electric organ discharges: low voltage and high voltage. These organs are made of electrocytes, lined up so a current of ions can flow through them and stacked so each one adds to a potential difference.

When the eel locates its prey, the brain sends a signal through the nervous system to the electrocytes. This opens the ion channels, allowing sodium to flow through, reversing the polarity momentarily. By causing a sudden difference in electric potential, it generates an electric current in a manner similar to a battery, in which stacked plates each produce an electric potential difference.

In the electric eel, some 5,000 to 6,000 stacked electroplaques are capable of producing a shock up to 860 volts and 1 ampere of current (860 watts) for a duration of two milliseconds. Such a shock is extremely unlikely to be deadly for an adult human, due to the very short duration of the discharge. Atrial fibrillation requires that roughly 700 mA be delivered across the heart muscle for 30 ms or more, far longer than the eel is able to produce. Still, this level of current is reportedly enough to produce a brief and painful numbing shock likened to a stun gun discharge, which due to the voltage can be felt for some distance from the fish; this is a common risk for aquarium caretakers and biologists attempting to handle or examine electric eels.

The Sach's organ is associated with electrolocation. Inside the organ are many muscle-like cells, called electrocytes. Each cell can only produce 0.15 V, though the organ can transmit a signal of nearly 10 V overall in amplitude at around 25 Hz in frequency. These signals are emitted by the main organ; the Hunter's organ can emit signals at rates of several hundred hertz.

The electric eel is unique among the Gymnotiformes in having large electric organs capable of producing potentially lethal discharges that allow them to stun prey. Larger voltages have been reported, but the typical output is sufficient to stun or deter virtually any animal. Juveniles produce smaller voltages (about 100 V). They are capable of varying the intensity of the electric discharge, using lower discharges for hunting and higher intensities for stunning prey or defending themselves. They can also concentrate the discharge by curling up and making contact at two points along its body. When agitated, they are capable of producing these intermittent electric shocks over a period of at least an hour without tiring.

The electric eel also possesses high frequency-sensitive tuberous receptors, which are distributed in patches over its body. This feature is apparently useful for hunting other Gymnotiformes.

Electric eels have been used as a model in the study of bioelectrogenesis. The species is of some interest to researchers, who make use of its acetylcholinesterase and adenosine triphosphate.

Glass knifefish

The Glass Knifefish (Eigenmannia virescens) is a weakly electric freshwater fish found across South America. It is marketed as an aquarium fish.

The appendix on the body has black lines running through the bottom of the sides, with the most intense line running on the anal fin.

Like all members of its order, it is distinguished by its ability to produce electric fields. This is achieved by discharging an electric organ in the tail.