Nematobrycon lacortei – Rainbow Tetra
Stanley H. Weitzman and William L. Fink first described Nematobrycon lacortei in 1971. This fish, commonly known as the Rainbow Tetra, belongs to the family Characidae, also known as characins.
The genus name Nematobrycon is derived from the Ancient Greek words “νῆμα” (nêma), meaning “thread,” which refers to the elongated, thread-like rays found in the caudal fin of species within this genus, and “βρύκω” (brúkhō), meaning “to devour, swallow, bite, chew, or gnash.” Initially, this term was used to describe the presence of fully toothed maxillae (upper jaws) in certain fish, but it was later applied to the generic names of various characiform species to indicate their perceived relatedness.
The species name lacortei is derived from Rosario LaCorte, an American aquarist who undertook five expeditions to South America from 1977 to 1988. He authored two books: “Enjoy Your Cichlids” (1969) and “An Aquarist’s Journey” (2018).
Description
The Rainbow Tetra (Nematobrycon lacortei) has a slender, streamlined body. Its head and flanks display an iridescent, rainbow-like coloration, complemented by a dark, often blackish-brown lateral stripe that runs from the mouth to the tail. The belly is typically lighter, appearing yellowish or beige. The fins are either transparent or lightly colored. A dark stripe may be present along the anterior edge of the dorsal fin, the upper edge of the caudal fin, and the outer edge of the anal fin. This species can reach a maximum total length of approximately 4 to 4.5 centimeters.
Sex differences can be observed in several areas. Males tend to be more colorful than females and have longer dorsal, anal, and caudal fins. A distinct feature is their eye color: males possess red eyes, while females have blue-green eyes. Behaviorally, males are more territorial and aggressive toward other males, whereas they are typically peaceful with other species. In contrast, females are generally less aggressive. Juvenile fish resemble females in terms of color and fin length; the characteristic red eyes and longer fins of males develop only as they grow older.
Behavior and Temperament: Rainbow Tetras are mostly peaceful schooling fish that thrive in groups of at least 6 to 10 individuals. This social behavior enhances both their natural habits and vibrant coloration. While generally docile, males may display territorial behavior towards each other, particularly in smaller tanks or if there are insufficient hiding places. These fish are not bottom dwellers; they primarily swim in the midwater. They are also quite active and can be easily observed in the aquarium.
Life expectancy: Life expectancy in the wild is not precisely known, but in an aquarium they can live 3 to 5 years, with some sources stating up to 5 years.
Habitat and Ecology
Nematobrycon lacortei is native to Colombia. It is found in the Rio San Juan basin, specifically in the Rio Calima, a tributary located in the lower part of the basin.
They are riverine fishes that inhabit small, isolated forest pools in the upper reaches of the Rio Calima, probably above the Calima Dam. The exact rivers and streams outside the Rio Calima and Rio San Juan are not specifically mentioned in the available documents.
Their natural habitat is characterized by an abundance of underwater vegetation in small, quiet tributaries. The banks are covered with trees, which provide shade and shelter. The soil probably consists of a mixture of sand, mud and organic matter
Information about their natural predators in the wild is limited in the documents provided, but they are likely prey for larger fish and other predators in their environment.
The Rainbow Tetra lives in a tropical climate with stable temperatures and humidity. Periods of flooding temporarily connect the rivers and small pools.
Diet
In the wild, the Rainbow Tetra (Nematobrycon lacortei) feeds on a varied diet of small invertebrates, insect larvae, and other small organisms found in their natural habitat. However, precise details about their diet in the wild are limited.
In an aquarium, fish should be fed a diverse diet that includes high-quality dry food, such as flakes or pellets, along with live or frozen foods like water fleas (Daphnia), brine shrimp (Artemia), and mosquito larvae. This varied diet promotes optimal growth and health. It’s important to limit the amount of food to what they can consume within a few minutes to prevent water pollution.
The Aquarium
A minimum aquarium size of 60 liters (15 gallons) is suitable for a group of 6 to 10 Rainbow Tetras. A larger aquarium is necessary for larger groups or multiple pairs, providing approximately 20 liters (5 gallons) per additional fish.
The decor should replicate a natural environment, featuring plenty of vegetation—both rooted and floating. Incorporating spindly driftwood and various hiding places is also advisable to provide the fish with a sense of security. Using a dark substrate, such as dark sand or fine gravel, can enhance the colors of the fish. It’s important to avoid sharp objects that could injure them.
Optimal water conditions include a pH level of 6.0-7.5, a temperature range of 22-28°C (72-82°F), and medium hardness. To maintain good water quality, regular water changes of 25% per week are essential.
Suitable tankmates include other small, peaceful fish such as other tetra species, small rasboras, and Corydoras species. Avoid larger or aggressive fish that might stress or attack the Rainbow Emperor Tetra. Long-finned fish are also not recommended, as the Rainbow Emperor Tetra tends to nibble fins.
Breeding Aquarium and Conditioning
Limited information is available on breeding Rainbow Tetras. To successfully reproduce them, it is important to set up a separate breeding tank. This tank should be small, providing enough space for a few fish and their eggs.
The water conditions in the breeding tank are crucial. It should be soft and acidic, preferably with a pH level between 5.0 and 7.0, and a medium hardness (GH 1-8). The ideal temperature for breeding should be around 24 to 27°C.
For water circulation, a small, air-driven sponge filter is recommended. This type of filter is gentle and will not harm the eggs or fry. Additionally, the sponge filter provides a surface for the fry to find tiny food organisms.
Lastly, keep the lighting dim to reduce stress for the fish during the breeding process.
To prepare for breeding, fish should be conditioned for several weeks with high-quality live or frozen foods, such as daphnia, brine shrimp, and mosquito larvae. This helps optimize their reproductive health. Once conditioned, a male and a female fish can be placed together in a breeding tank. If necessary, temporary separation for further conditioning is an option.
The Spawn
The males’ colors become more vibrant during courtship. They display increased territorial behavior to attract female attention.
The eggs are laid on fine leaves of plants like Java moss or on a spawning mop. Spawning likely occurs in the morning or early afternoon, and the eggs are deposited in the open. After laying their eggs, the parents will eat them, so it’s important to remove them and place the parents back in their own aquarium.
Raising the Young Fish
Rainbow Tetra eggs hatch within 24 to 36 hours, and the fry begin swimming freely 4 to 5 days after hatching.
During the first week, provide the fish with the smallest food types, such as infusoria. After this initial period, once they have grown a bit, you can introduce Microworms and Artemia nauplii into their diet. To maintain water quality, it is recommended to perform regular small water changes, such as 10% each week. The survival rate of the fish significantly depends on water quality, the quantity and quality of the food provided, and protection from excessive light. To help create a darker environment, it’s beneficial to include plenty of aquatic plants in the aquarium.
Particularities
There are some peculiarities about the Rainbow Tetra (Nematobrycon lacortei) that are worth mentioning:
- Rarity: The Rainbow Tetra is a relatively rare fish in the aquarium trade. This is because they are not commercially bred but mainly imported from the wild. This often makes them more expensive than other tetra species.
- Confusion with Nematobrycon palmeri: The Rainbow Tetra is often confused with the Nematobrycon palmeri (Emperor Tetra). Although they look similar, especially as young fish, adults show distinct differences in color pattern and eye color.
- Color Intensity: The iridescent colors of the Rainbow Tetra are enhanced by proper aquarium conditions, such as soft, acidic water and dim lighting. Adding dried leaves of the Indian almond tree (Terminalia catappa) can further enhance color intensity.
- Territoriality: Although generally peaceful, males may display territorial behavior, especially in smaller tanks or when there are fewer hiding places. Keeping a large group (at least 6-10, preferably more) will greatly reduce this behavior.
- Breeding Challenges: Breeding Rainbow Tetras in captivity is difficult. Females lay only a few eggs at a time and often eat their eggs. A separate breeding tank with soft, acidic water parameters and plenty of plants is essential for success.
- Diet: Although not fussy, a varied diet of high quality dry food, supplemented with live or frozen food, is essential for their health and well-being.
- Suitable Tankmates: The Rainbow Tetra is compatible with other small, peaceful fish species, but it is important to avoid long-finned fish to prevent fin-nipping.
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Author
John de Lange
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