Gymnotus carapo – Banded Knifefish
Gymnotus carapo, also known as the Banded Knifefish, was first described by Carl Linnaeus in 1758. This fish belongs to the family Gymnotidae, which are known as the Knifefishes. The family Gymnotidae consists of two genera, Gymnotus and Electrophorus, which together currently contain 45 species.
The genus name Gymnotus is derived from the Greek word “gymnos,” meaning “naked,” referring to the absence of scales on the back of these fish. The species name “carapo” has no specific etymological meaning; it is the local name for Knifefish in South America.
Synonyms: Gymnotus fasciatus, Gymnotus brachiurus, Gymnotus putaol, Carapus macrourus.
Description
General Description:
Gymnotus carapo has an elongated, cylindrical body that gradually merges into a rod-shaped, finless tail. The fish is brown with a pattern of light and dark brown transverse bands that are slightly oblique. The anal fin is long and light brown, and extends from behind the head to the end of the tail. The body length can reach 60 centimeters.
Differences between Males and Females:
There are no obvious physical differences between males and females. Both sexes exhibit similar colors and patterns. Behaviorally, males are responsible for caring for the young.
Behavior and Temperament:
Gymnotus carapo is a nocturnal fish that can be very aggressive toward its own kind but is relatively peaceful toward other and larger fish. Smaller fish are sometimes seen as food. They can generate weak electrical currents to sense their surroundings and move by undulating movements of the anal fin.
Life Expectancy:
In the wild, these fish can live for several years, but in a well-maintained aquarium, they can potentially live longer depending on care and conditions.
Use of Weak Electrical Currents
Navigation and Environmental Sensing:
Gymnotus carapo uses its electrical currents primarily for navigation and detecting objects in its environment. This process is known as electrolocation. The fish emits a weak electrical pulse and senses disturbances in its electrical field caused by nearby objects. These disturbances provide the fish with information about the size, shape, and distance of objects, allowing it to orient itself and avoid obstacles.
Communication:
Electrical currents are also used for communication with conspecifics. Gymnotus carapo can use variations in the frequency and pattern of the electrical pulses to send signals to other fish. This is especially important for territorial behavior and during reproduction, when males defend their territory and attract females.
Food Search:
In addition, the electric current helps the fish find prey. Small prey such as insect larvae, worms, and small fish disrupt the electric field, allowing Gymnotus carapo to locate and capture them.
Generation of Electric Currents
Electric Organ:
Electric currents are generated by a specialized organ known as the electric organ. This organ is located along the sides of the fish’s body and is made up of electrolytes, specialized cells that can build up and discharge electrical charges. When these cells discharge synchronously, they generate an electrical pulse.
Mechanism of Discharge:
The discharge process begins when nerves send signals to electrocytes, prompting ion channels in the cell membranes to open. This action leads to a rapid movement of ions, generating an electric current. Fish can adjust the frequency and pattern of these discharges based on the situation, such as when navigating complex environments or communicating with other fish.
Electroreceptors:
In addition to generating electrical currents, the Striped Knifefish also has electroreceptors that are sensitive to electric fields. These receptors are located primarily on the head and along the sides of the body. They detect changes in the electric field caused by external objects and other fish, allowing the fish to form a detailed picture of its surroundings.
Biotope
Distribution and Habitat:
Gymnotus carapo is found in northern and central South America, including countries such as Venezuela, Suriname, Uruguay, and Trinidad. They live in a variety of freshwater habitats such as rivers, streams, lakes, and swamps, but not in deep river channels.
Natural Habitat:
These fish are often found in areas with lots of underwater vegetation and densely vegetated shorelines. The bottom is usually mud or sand. They can survive in oxygen-poor environments and are resistant to pollution.
Natural Enemies:
Gymnotus carapo has few natural enemies due to its ability to generate electrical currents, which aids in detecting and avoiding predators. They themselves are hunters, feeding on small fish, insects, and other invertebrates.
Climate:
They live in a tropical climate with seasonal floods and droughts, which affect their reproductive and survival strategies.
Diet
Diet in the Wild:
Gymnotus carapo feeds on benthic organisms such as worms, insects, crustaceans, small fish, and plant material.
Aquarium Diet:
In an aquarium, they can be fed a varied diet of live foods such as worms, insect larvae, and small fish. They can also be fed high quality dry and frozen foods, but they must be acclimated to these foods before they will eat them. Some specimens will never accept non-living foods.
The Aquarium
Aquarium size:
For one Gymnotus carapo an aquarium of at least 200 centimeters in length is recommended. For multiple specimens, a larger aquarium of at least centimeters in length is necessary to minimize territorial conflicts.
Aquarium Setup:
The aquarium should be set up with lots of hiding places, such as rocks, wood, and dense planting. A sand or fine-gravel substrate is ideal. Provide a well-filtered and oxygenated aquarium with a pH between 6.0 and 7.5 and a temperature of 24-25°C.
Suitable Tankmates:
The Striped Knifefish does well with peaceful, medium-sized fish such as tetras, corydoras, and some cichlids. Avoid aggressive or very small fish that may be considered prey.
Breeding aquarium and conditioning
Breeding conditions:
Gymnotus carapo can be bred in a normal aquarium, but a special breeding tank of at least 100 liters is recommended. The water should be clean and well filtered, with a temperature of 24-25°C and a pH of 6.0-7.5. Use a sponge filter to protect the fry from being sucked in.
Conditioning:
Condition the fish with a diet of live foods such as worms and insect larvae. Temporarily separating the male and female and then reintroducing them to encourage breeding is helpful.
The Spawn
Colors and Courtship:
During spawning, the colors of the fish become more intense. The male digs a nest in the substrate or uses the roots of aquatic plants. Mating usually takes place in the evening. The eggs are laid in a nest and the male guards them. About 100-200 eggs are laid, which are small and transparent.
Raising the fry
Hatching and Free Swimming:
The eggs hatch after about 3-4 days. The fry begin to swim freely after about a week. The male cares for the fry by protecting and guiding them. The fry can be fed with infusoria and later with baby brine shrimp. Water changes should be performed regularly to maintain high water quality. About 50-70% of the fry survive with good care.
Conclusion
Gymnotus carapo is a fascinating fish species that is suitable for advanced aquarium enthusiasts. They require specific care and a large aquarium due to their aggressive nature and territorial behavior. Breeding this species can be challenging, but it offers a unique opportunity to observe their interesting breeding behavior. In general, they are robust fish that can thrive in a well-maintained aquarium.
Video
Author
John de Lange
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