Epalzeorhynchos frenatum (Green Fringe Lark / Rainbow Shark)

02 August 2026

327

The Green Fringe Lark, widely known as the Rainbow Shark, is a striking freshwater cyprinid native to Southeast Asia. Famous for its vibrant red fins contrasting against a dark body, this semi-aggressive bottom-dweller brings dynamic activity to large aquariums, though its territorial nature requires careful tank mate selection.

Epalzeorhynchos frenatum (Green Fringe Lark / Rainbow Shark)

Overview

The Green Fringe Lark, more commonly known in the aquarium trade as the Rainbow Shark or Ruby Shark, is a highly popular freshwater fish. Despite the "shark" moniker, it is actually a species of cyprinid. Known for its striking contrast of a dark body and fiery red fins, it adds a brilliant splash of color and high energy to the lower levels of a suitably sized aquarium.

Distribution and Habitat

This species is native to the river basins of Southeast Asia, primarily found in Thailand, including the Mekong, Chao Phraya, and Mae Klong basins. They inhabit the sandy and rocky bottoms of rivers and streams where they graze on algae and biofilm. During the rainy season, they are known to migrate into flooded areas.

Image of green fringe lark epalzeorhynchos frenatum

Description of Green Fringe Lark

Body shape:

They possess an elongated, torpedo-like body that gives them a distinctly shark-like silhouette. The ventral profile is relatively flat, which is ideal for a bottom-dwelling lifestyle.

Color:

The main body exhibits a dark grey to olive-green or brownish coloration. Depending on the lighting and the fish's mood, the body can appear almost black or take on a subtle greenish hue.

Barbels:

As seen closely in their facial structure, they have two pairs of short, sensitive barbels protruding from the corners of their mouth, which help them locate food in the substrate.

Snout:

The snout is pointed with a slightly downturned mouth, perfectly adapted for grazing and scraping algae off flat surfaces.

Eyes:

They have relatively large, alert eyes with a dark pupil surrounded by a lighter, sometimes golden ring.

Fins:

All of the fins—dorsal, pectoral, pelvic, and anal—are a vibrant, striking red or deep orange, providing a beautiful contrast to the muted body color.

The Tail:

The caudal fin (tail) is deeply forked and shares the same vivid red/orange coloration as the other fins. A distinct dark, almost black patch is often visible right at the base of the caudal peduncle.

Temper

The Green Fringe Lark is considered semi-aggressive. While they are generally indifferent to fish that occupy the upper water column, they are highly territorial when it comes to the bottom of the tank.

Sociality

This is a solitary species that does not play well with its own kind or other shark-like fish (such as Red Tail Sharks or Flying Foxes). Keeping more than one in a standard aquarium almost always results in severe aggression and dominance disputes. They should be kept as the sole bottom-dwelling "shark" in the tank.

Activity

They are incredibly active and industrious fish. You will constantly see them darting around the lower levels of the tank, patrolling their territory, and grazing on decorations, plants, and the substrate.

Keeping and Caring for Green Fringe Lark

Tank size:

Due to their adult size of up to 15 cm and their highly territorial nature, a minimum tank size of 55 gallons (approx. 200 liters) is required. A larger footprint is always better to provide ample grazing space.

Water Parameters:

Temperature

They thrive in tropical temperatures ranging from 22-28°C (72-82°F).

pH

The ideal pH should be kept slightly acidic to neutral, between 6.5 and 7.5.

Hardness

Water hardness should be maintained between 5 and 15 dGH.

Ammonia, Nitrite, Nitrate

Ammonia and Nitrite must always be at 0 ppm. Nitrates should be kept as low as possible, ideally below 20 ppm, through regular water changes.

Lighting

Moderate lighting is preferred. If the lighting is too intense, ensure there is plenty of shaded cover provided by plants or hardscape.

Water flow

As a riverine species, they appreciate moderate to moderately strong water flow to simulate their natural environment.

Decorations and Plants

The tank must have plenty of hiding spots. Use smooth rocks, driftwood, and PVC pipes to create caves. Dense planting is highly recommended to break the line of sight and help reduce territorial aggression towards other tank mates.

Diet

They are omnivorous scavengers. In the wild, they consume algae, insect larvae, and zooplankton. In the aquarium, they will readily accept high-quality sinking pellets, algae wafers, and occasional live or frozen foods like bloodworms and brine shrimp.

Some Feeding Tips

Ensure that food actually reaches the bottom of the tank before mid-water fish consume it all. Feeding them right before turning the tank lights off can help ensure they get their share without competition.

Breeding

Breeding the Green Fringe Lark in a home aquarium is extremely difficult and rarely achieved due to their intolerance of one another. In commercial settings, breeding is typically induced using hormone injections in large outdoor ponds.

Conclusion

The Green Fringe Lark (Rainbow Shark) is a visually stunning and fascinating fish that makes a great centerpiece for a large, semi-aggressive community aquarium. As long as their territorial requirements are respected and they are provided with plenty of space and hiding spots, they will be a hardy and entertaining addition to your aquatic setup.

Fish info

Care level: Moderate
Temperament: Semi-aggressive
Adult size: 15 cm
Life expectancy: 5-8 years
Fish type: Cyprinid
Temperature : 22-28°C
pH: 6.5-7.5
Color Form: Black, Green, Grey, Orange, Red

Related on Fishs

Leave your comments

Latest on Fishs

White Marble Angelfish (Pterophyllum scalare)

Moderate

Freshwater cichlid

The white marble angelfish is a selectively bred aquarium color form of Pterophyllum scalare, a tall-bodied South American cichlid valued for its elegant fins and distinctive irregular dark marbling. It is generally peaceful when young but can become territorial, especially when paired for spawning. Successful care depends on a tall aquarium, excellent water quality, suitable tank mates, and a varied carnivorous-omnivorous diet. The exact genetic strain shown cannot be confirmed from photographs alone.
Freshwater Angelfish Mix (Pterophyllum scalare)

Moderate

Freshwater cichlid

Freshwater angelfish are tall-bodied South American cichlids valued for their graceful movement and wide range of captive color forms. The supplied source identifies a mixed group as Pterophyllum scalare; the photographs show several forms, including striped, black, orange, white, silver and blue-toned fish. They are manageable for experienced beginners, but their adult height, territorial breeding behavior and tendency to eat small tank mates require thoughtful aquarium planning.
Leopard Angelfish (Pterophyllum scalare)

Moderate

South American freshwater cichlid

The leopard angelfish is a domestic color form of Pterophyllum scalare, a tall-bodied freshwater cichlid from tropical South America. Its silver to yellowish body is marked with irregular dark spots or broken vertical bars, although pattern intensity varies with age, mood and breeding line. It is generally peaceful in a suitably spacious community aquarium, but pairs become territorial when spawning. This fish needs warm, clean water, generous vertical swimming space and tank mates too large to swallow.
Yellow Labidochromis (Labidochromis caeruleus)

Easy - Moderate

Lake Malawi mbuna cichlid

The Yellow Labidochromis is a bright yellow mbuna cichlid from Lake Malawi. Labidochromis caeruleus is generally manageable for an African cichlid, but it remains territorial and needs hard, alkaline water, rockwork, and carefully chosen companions. The supplied source identifies two fish as a pair; sex and pair bonding cannot be confirmed from the available images. This species is an adaptable algae grazer, a maternal mouthbrooder, and a rewarding choice for an appropriately planned Malawi cichlid aquarium.
Blue Pearl Angelfish (Pterophyllum scalare)

Moderate

Freshwater cichlid

The Blue Pearl Angelfish is a selectively bred colour form of Pterophyllum scalare, the freshwater angelfish. Its laterally compressed body, extended fins and tall profile make it a striking inhabitant of a planted community aquarium. The supplied trade label supports identification as this species and colour form, although individual colour intensity can vary. It requires warm, stable, clean water, generous vertical swimming space and thoughtful tank-mate selection, especially as adults become territorial when pairing or spawning.
Villavicencio Dwarf Cichlid Apistogramma macmasteri

Moderate

South American dwarf cichlid

Apistogramma macmasteri, commonly called the Villavicencio dwarf cichlid, is a small South American cichlid associated with the Río Orinoco drainage of Colombia. It is valued for its compact size, elaborate finnage and interesting courtship behavior. A bonded pair can be kept in a carefully structured aquarium with soft, clean water, sand, cover and several potential spawning sites. Although manageable for an experienced community aquarist, territorial behavior increases during breeding, so tank layout and tankmate selection are important.
Neolamprologus leleupi (Tanganyika Golden Cichlid)

Moderate

Lake Tanganyika rock-dwelling cichlid

Neolamprologus leleupi is a small, brightly coloured cichlid endemic to Lake Tanganyika in East Africa. It inhabits rocky coastal areas and uses crevices for shelter, feeding and spawning. Despite its modest size, it can be strongly territorial, particularly when paired or breeding. The supplied source identifies these fish as a golden colour form and a pair, although sex cannot be confirmed reliably from the image alone. Successful care depends on alkaline, mineral-rich water, abundant rockwork and carefully chosen tank mates.
Maingano Cichlid (Melanochromis cyaneorhabdos)

Moderate - Difficult

Lake Malawi mbuna cichlid

The Maingano, or Johanni Maingano, is a Lake Malawi mbuna recognized for its intense steel-blue body and dark horizontal markings. The supplied label combines “Johanni” with the scientific name Melanochromis cyaneorhabdos; these are distinct species, so identification should be confirmed from the seller or locality. This territorial mouthbrooding cichlid needs hard, alkaline water, abundant rockwork, a predominantly algae-based diet, and careful stocking to limit aggression.
Red Chocolate Gourami (Sphaerichthys vaillanti)

Difficult

Blackwater labyrinth fish

The red chocolate gourami, Sphaerichthys vaillanti, is a specialized Southeast Asian labyrinth fish suited to mature, soft, acidic blackwater aquariums. It is peaceful but easily stressed by bright lighting, strong currents and boisterous tank mates. The supplied source identifies these fish as a pair; sex and exact identity cannot be confirmed from the image alone, so identification should be checked against a reliable specimen reference. Stable water quality, cover and a varied small-food diet are central to long-term success.
Pelvicachromis pulcher Purple Tilapia Pair Care Guide

Easy - Moderate

Small West African freshwater cichlid

Pelvicachromis pulcher, commonly called the kribensis or purple cichlid, is a small West African cave-spawning cichlid valued for its manageable size, attractive breeding colors and attentive parental behavior. A bonded pair can live in a community aquarium when provided with suitable cover and carefully chosen tank mates. The supplied listing identifies the fish as Pelvicachromis pulcher, although photographs alone cannot confirm the exact locality or color form.
Red Lined Dwarf Cichlid (Apistogramma hongsloi)

Moderate

Dwarf Cichlid

The Red Lined Dwarf Cichlid, Apistogramma hongsloi, is a small, colorful South American cichlid highly regarded by hobbyists. Native to the Orinoco River basin, this species displays striking red markings and elegant finnage. Known for their interesting social behaviors and relatively peaceful nature, they make excellent subjects for planted community aquariums that provide appropriate hiding spots and soft, acidic water conditions.
Apistogramma panduro

Moderate

Dwarf Cichlid

The Panduro dwarf cichlid, Apistogramma panduro, is a striking South American species highly prized for its vibrant coloration and manageable size. Native to the Amazon basin, this species exhibits distinct sexual dimorphism. They are best kept in pairs or small groups within well-structured aquariums, making them a fascinating choice for dedicated hobbyists interested in cichlid behavior and breeding dynamics.
Opal Apistogramma (Apistogramma borellii)

The Opal Apistogramma is a stunning, selectively bred color variant of the popular Apistogramma borellii. Native to South American river basins, these dwarf cichlids are prized for their vibrant blue coloration and striking red facial markings. They are excellent candidates for planted community aquariums, provided their specific water quality and territorial requirements are carefully maintained by the aquarist.
Macropodus opercularis (Paradise Fish)

The Paradise Fish, Macropodus opercularis, is a classic labyrinth fish native to East Asia. Known for its striking striped coloration and complex behavior, this species was one of the first exotic fish introduced to the aquarium trade. While beautiful, they are known for their territorial nature, requiring careful tank mate selection and sufficient space to thrive in captivity.
Altolamprologus calvus (Black)

The Altolamprologus calvus, commonly known as the Black Calvus or Guinea Fowl Cichlid, is a distinct cichlid species endemic to Lake Tanganyika in Africa. Renowned for its laterally compressed body and unique, predatory hunting behavior, it is a fascinating choice for experienced aquarists. These fish are slow-growing and demand specific environmental conditions to thrive in a captive setting.
Mesonauta festivus (Flag Cichlid)

The Flag Cichlid, Mesonauta festivus, is a popular South American cichlid known for its distinct diagonal stripe and calm demeanor. Often found in the Amazon basin, this species is highly appreciated by aquarists for its unique appearance and relatively peaceful social structure. It thrives in well-maintained planted tanks, provided they have sufficient swimming space and appropriate water conditions for their long-term health.