Astyanax bimaculatus (LINNAEUS, 1758) – Two Spot Astyanax

Classification

The Characiformes order and Characidae family are among the most diverse and widespread groups of freshwater fish found around the world. These fish are known for their unique physical features, active behavior, and diverse range of species, many of which are popular among aquarium hobbyists.

The Characiformes order includes over 2,000 species of fish that are widely distributed in tropical and subtropical regions around the world. Members of this order are characterized by a number of unique physical features, including an adipose fin, a small, fleshy fin located on the back of the fish just in front of the tail fin. They also typically have a number of small teeth arranged in rows in their jaws, which they use to capture and consume prey. Additionally, many species in this order have a streamlined body shape, which helps them to move quickly through the water.

Within the Characiformes order, the Characidae family is the largest and most diverse. This family includes over 1,500 species of fish that are typically small to medium-sized, with most species measuring between 1 and 6 inches in length. Characidae fish are generally found in rivers, streams, and other freshwater environments, and many species are known for their schooling behavior. Some species are also migratory and may move between different habitats during different stages of their life cycle.

Characidae fish are known for their vibrant colors and active swimming behavior, making them a popular choice among aquarium hobbyists. Some of the most commonly kept species of Characidae include tetras, hatchetfish, and pencilfish. These fish are generally hardy and easy to care for, making them a good choice for both beginners and experienced fish keepers.

In terms of their diet, Characidae fish are typically omnivorous, consuming a wide range of both plant and animal matter. Some species are herbivorous and primarily feed on algae and other plant matter, while others are carnivorous and primarily feed on small invertebrates and other fish.

One of the most distinctive features of Characidae fish is their ability to form large schools in the wild. Schooling behavior helps these fish to avoid predators, and also helps them to find food and mates more easily. Some species of Characidae fish are also known for their unique breeding behavior, which may involve elaborate courtship displays, nest building, or other complex behaviors.

In summary, the Characiformes order and Characidae family are a diverse and important group of freshwater fish. These fish are known for their unique physical features, active behavior, and diverse range of species, many of which are popular among aquarium hobbyists. They play an important role in the freshwater ecosystems where they are found, and their unique behaviors and adaptations make them a fascinating subject of study for fish enthusiasts and scientists alike.

Distribution

The exact location of the type locality for this species remains unknown, but it is widely distributed across a vast range of territory throughout South America. Its distribution extends from Panama throughout the Amazon and Orinoco river basins, covering a significant portion of the continent.

This species has been recorded in many countries across South America, including Trinidad and Tobago, Colombia, Venezuela, Guyana, Suriname, French Guiana, Ecuador, Peru, Brazil, and Argentina. Its ubiquitous nature means that it is found in a wide variety of freshwater habitats throughout its range.

In Panama, this species can be found in various water systems, such as rivers, streams, and lakes. In the Amazon basin, it is commonly found in blackwater rivers, which are characterized by low pH levels and high concentrations of dissolved organic matter. In the Orinoco river basin, it is typically found in clearwater rivers, which have a higher pH and lower concentrations of dissolved organic matter than blackwater rivers.

Throughout its range, this species can inhabit a range of freshwater habitats, from large rivers to small streams and floodplains. It can also be found in areas with different water conditions, such as clear or murky waters. This species is known for its ability to adapt to changes in water temperature, pH, and oxygen levels, making it a resilient and versatile species.

The adaptability of this species has allowed it to become ubiquitous throughout much of its range. It is found in a wide variety of habitats and can thrive under different environmental conditions. Its presence across much of South America highlights the ecological importance and widespread impact of this species on freshwater ecosystems throughout the continent.

Habitat

This species is capable of thriving in a diverse range of freshwater habitats, including swiftly-flowing rivers and streams, ponds, ditches, and reservoirs. It is adaptable to different water conditions, making it a resilient species.

Many of the habitats in which this species can be found display significant seasonal differences in water volume and depth. During periods of heavy rainfall, the water volume and depth may increase, while during dry periods, water levels may decrease significantly. Despite these changes, this species is able to adapt to the changing conditions and continue to thrive in these habitats.

In swiftly-flowing rivers and streams, this species is typically found in areas with moderate to fast currents, such as riffles or runs. These areas provide an abundance of food and oxygen-rich water, allowing this species to grow and thrive.

In ponds and ditches, this species can be found in areas with still or slow-moving water. These habitats may have more vegetation and organic matter, which can provide shelter and food for this species.

In reservoirs, this species can be found in areas with deeper water, as well as areas with shallower water and submerged vegetation. These habitats can provide a variety of different food sources and can support a diverse ecosystem.

In general, this species is capable of adapting to a wide variety of biotopes, ranging from swiftly-flowing rivers and streams to ponds, ditches, and reservoirs. It is able to thrive in habitats with significant seasonal differences in water volume and depth, making it a resilient and adaptable species.

Maximum Standard Length

The maximum standard length that this species can reach is between 100 to 150 mm. Standard length refers to the measurement of the fish from the tip of its snout to the end of its caudal fin, while excluding the length of the adipose fin.

The size that this species can reach can vary depending on various factors, including genetics, diet, and environmental conditions. In some cases, individuals may not reach the maximum size due to factors such as predation or competition for resources.

At the lower end of the size range, individuals may be around 100 mm in length, while at the upper end of the size range, individuals may reach up to 150 mm in length. In general, larger individuals tend to be older and may have reached sexual maturity.

It’s important to note that while 100 to 150 mm is the maximum standard length that this species can reach, the average size may be smaller. Additionally, size can vary among populations of the species, as well as between males and females.

Aquarium Size

The recommended aquarium size for this species is dependent on their potential size and active nature. In order to accommodate their natural behavior and ensure their overall health, it is recommended that a tank with a base dimension of at least 120 cm x 60 cm or equivalent should be used.

The dimensions of the tank are important as they allow the fish to swim and move around freely. This is important for their physical and mental well-being. The base dimensions of the tank should not be less than the recommended size, as a smaller tank may cause the fish to become stressed and agitated, and may lead to health problems.

While a larger tank is recommended, the overall size and number of fish that can be kept in the tank will depend on other factors such as filtration, water quality, and the presence of hiding places and other environmental enrichment. These factors should also be considered when determining the appropriate tank size and number of fish to keep. Overcrowding or poor water quality can lead to stress, disease, and other health problems for the fish.

In addition to providing enough space, it’s also important to consider the swimming behavior of the fish. This species is known for its active swimming behavior, and requires adequate space to move around and explore its surroundings. A larger tank with enough open swimming space can help to promote natural swimming behavior and reduce the risk of injury or stress.

Hence, providing a tank with base dimensions of at least 120 cm x 60 cm or equivalent is a good starting point for keeping this species in an aquarium. However, it’s important to consider other factors as well when determining the appropriate tank size and number of fish to keep, such as filtration, water quality, and swimming behavior. Providing the appropriate environment and space for this species can help to promote their overall health and well-being in the aquarium.

Maintenance

Maintenance for this species is not considered critical, but providing a suitable environment is important to ensure their overall health and well-being. The main priority for maintaining this species is to provide plenty of swimming space, as they require adequate space to move around and explore their surroundings.

Décor in the aquarium can consist of driftwood branches and twisted roots with some rounded stones. These natural elements can provide hiding places and environmental enrichment for the fish. However, it’s important to ensure that these elements do not take up too much space in the aquarium, as this could limit the swimming area for the fish.

Plants are not typically recommended for this species, as they are likely to be eaten. However, some tougher-leaved genera such as Anubias or Microsorum may be able to survive in the aquarium. If plants are added, it’s important to ensure that they are not taking up too much space or limiting the swimming area for the fish.

Positioning the filter outlet is also important for maintaining a suitable environment for this species. The filter outlet should be positioned so that there is a degree of current flowing through the tank. This will help to promote a healthy and oxygen-rich environment for the fish, and also simulate their natural environment.

In summary, maintenance for this species is not overly demanding, but it’s important to ensure that the aquarium provides enough swimming space and suitable decor to promote the natural behavior of the fish. By providing a healthy and stimulating environment, this species can thrive in the aquarium and display their natural behaviors.

Water Conditions

The water condition for this species should be carefully maintained in order to promote their overall health and well-being. The recommended temperature range for this species is between 20 to 28°C, with a pH range between 5.5 to 7.5, and a hardness range between 36 to 357 ppm.

Temperature is an important factor to consider when keeping this species. The recommended range is relatively wide, but it’s important to maintain a stable temperature within this range to avoid stressing the fish. A heater can be used to maintain a stable temperature, and a thermometer can be used to monitor the water temperature.

The pH range recommended for this species is between 5.5 to 7.5. This range is slightly acidic to neutral, and can be achieved through the use of appropriate buffering agents or additives. It’s important to avoid sudden changes in pH, as this can cause stress and health problems for the fish.

Hardness, which refers to the amount of dissolved minerals in the water, should be maintained within a range of 36 to 357 ppm. A water test kit can be used to monitor the hardness level of the water, and appropriate additives can be used to adjust the hardness level if necessary.

Overall, it’s important to carefully monitor and maintain the water condition for this species in order to promote their overall health and well-being. Maintaining a stable temperature, pH, and hardness level can help to reduce stress and promote a healthy environment for the fish.

Diet

The diet of this species is relatively unfussy and omnivorous in nature, as they feed on both invertebrates and plant material in the wild. To replicate their natural diet in captivity, a variety of live and frozen foods should be offered regularly. However, good quality dried products can also serve as a staple diet for this species.

In order to provide a varied diet for this species, it’s recommended to offer a range of live or frozen foods such as brine shrimp, daphnia, bloodworms, and chopped earthworms. These foods should be offered regularly, as they provide important nutrients and help to stimulate natural feeding behaviors.

In addition to live and frozen foods, high-quality dried foods can also be offered as a staple diet. This can include commercially available flake, pellet, or granular foods that are specifically designed for freshwater fish. It’s important to choose a high-quality product that provides a balanced and varied diet, as well as to avoid overfeeding.

It’s worth noting that while this species is omnivorous, they may have a preference for certain types of food. Observing their feeding behavior and adjusting their diet accordingly can help to ensure that they are receiving the appropriate nutrients and remain healthy.

In conclusion, providing a varied diet of live or frozen foods, along with high-quality dried products, can help to replicate their natural diet in captivity and promote their overall health and well-being.

Behaviour and Compatibility

When selecting tankmates for this species, it’s important to consider its adult size and active nature. Although not inherently aggressive, this species may still pose a threat to smaller or very slow-moving fish in the aquarium. As a result, it’s recommended to avoid including such fish in the same tank as this species.

In larger aquariums, this species can be a unique and interesting addition to a community of fish. However, it’s important to ensure that the tank is spacious enough to accommodate this species and its potential tankmates comfortably. A crowded environment can lead to increased stress levels and potential aggression among fish, so providing ample swimming space is important for maintaining a harmonious community.

It’s also important to consider the activity level of potential tankmates when choosing fish to keep with this species. Fish that are similar in size and activity level are more likely to coexist peacefully with this species, as they are less likely to be perceived as prey or as a threat.

Overall, while this species is not considered highly aggressive, it’s important to carefully consider its adult size and active nature when selecting tankmates. In larger aquariums, this species can add interest and variety to a community of fish, but it’s important to ensure that the tank is large enough and that tankmates are well-matched in size and activity level to promote a harmonious environment.

Sexual Dimorphism

Female fish of this species can be easily identified by their noticeably round belly when full of eggs, and they tend to be a little less colorful than males.

During the breeding season, female fish will produce eggs, causing their belly to become visibly round. This is a natural process that indicates the readiness of the female to breed. Observing this characteristic can help to determine when the female is ready to spawn.

In addition to their physical appearance during the breeding season, female fish can also be identified by their less vibrant coloration when compared to males. This difference in coloration is a natural characteristic of this species, and can be used to distinguish between the sexes.

It’s important to note that while there are physical differences between male and female fish, they should be treated equally in terms of their care and well-being. Ensuring a healthy and suitable environment for all fish in the aquarium is important for their overall health and longevity.

Reproduction

To breed this species, the most successful method involves using a 2:1 ratio of males to females. It’s recommended to add some bunches of fine-leaved plants such as Cabomba or Java moss to act as a spawning medium, although little or no lighting is required.

In addition to the plants, an air-driven sponge filter can also be installed in the spawning tank to help maintain water quality. Before breeding, it’s best to condition the fish in a separate tank with lots of live foods to ensure they are healthy and ready to breed.

Once the females are plump with eggs, one female and a couple of males can be added to the spawning tank. Spawning usually occurs the following morning, with a single female capable of producing several thousand eggs. The eggs hatch in around 24 hours, and the fry may become free-swimming as little as 12 hours later.

To feed the newly hatched fry, it’s recommended to begin with newly hatched Artemia, and later introduce powdered dried foods if desired. Growth is fairly rapid provided regular water changes are carried out to maintain water quality.

In general, breeding this species involves a specific set of conditions and careful attention to water quality and feeding. By providing a suitable environment and following these guidelines, successful breeding can be achieved.

Notes

A. bimaculatus is not a particularly common aquarium fish, and is generally only available on occasion, typically as a contaminant in shipments of other fish species. As a result, this species is not well-known or widely kept by hobbyists.

One factor that complicates the care and keeping of A. bimaculatus is the uncertainty surrounding its taxonomic status. It is currently considered to be a species complex comprising at least four different taxa. This means that there may be some confusion regarding the specific characteristics and care requirements of this species.

While the exact care requirements for A. bimaculatus may not be well-understood, it’s important to remember that this species is still a living animal and requires proper care and consideration in order to thrive. It’s recommended to obtain this species from a reputable source and to do thorough research on its specific care requirements before attempting to keep it in an aquarium.

Despite its uncertain taxonomic status and limited availability, A. bimaculatus can still be an interesting and unique addition to a suitable aquarium environment. For those interested in keeping this species, it may require some extra effort and attention to ensure that its specific needs are being met. With the proper care and consideration, however, this species can thrive and display its natural behaviors in the aquarium.