Redtail Goodeid (Redtail Splitfin) 101: The Ultimate Care Guide

Redtail Goodeid (Xenotoca eiseni) originates from the fast-flowing rivers and streams of Western Mexico. 

Known for their captivating coloration and intriguing behavior, they add a splash of vibrancy to any aquarium. 

Unfortunately, these alluring fish are facing threats like pollution and habitat loss in the wild.

But in this article, I’ll walk you step by step through creating the perfect environment for these fascinating fish in your home aquarium. 

Redtail Goodeid Summary

Common NamesRedtail Goodeid, Redtail Splitfin
Scientific NameXenotoca eiseni
ColorMales have vibrant red-orange tails with a blue sheen, while females are generally more muted in coloration, with olive-brown or greenish-gray bodies
Size2.5 to 3 inches (6.4 to 7.6 cm)
Lifespan3 to 5 years
pH Level7.0 and 8.0
Water Temperature70°F to 75°F (21°C to 24°C)
Water Hardness10 to 20 dGH
Water TypeFreshwater
Minimum Tank Size20 to 30 gallons
Community TankThey can be kept in a community tank with peaceful fish species of similar size and temperament. Avoid housing them with aggressive or fin-nipping species.
Care LevelModerate 
CompatibilityCompatible with other peaceful fish species

Redtail Goodeid History

The Redtail Goodeid (Xenotoca eiseni), also known as the Redtail splitfin, is part of the Goodeidae family, a group of live-bearing fish species that are predominantly found in Mexico.

In 1898, David Starr Jordan first discovered the Redtail Goodeid in the freshwater streams and rivers of the Mexican Pacific Slope, specifically in the states of Jalisco, Colima, and Michoacán. 

Jordan, an eminent ichthyologist, was captivated by the vibrant red tail and the striking blue sheen of the males, hence the name ‘Redtail Goodeid’.

Over the years, the Redtail Goodeid has gained recognition in the aquarium hobby due to its unique appearance and interesting breeding habits. 

However, their story is not just one of fascination and beauty, but also of survival. 

The natural habitats of the Redtail Goodeid have faced significant threats due to human activities, including water pollution, habitat degradation, and overfishing. 

As a result, the wild populations of this species have been declining, and the Redtail Goodeid is currently classified as ‘Vulnerable’ on the IUCN Red List of Threatened Species.

In response to these challenges, numerous conservation efforts have been implemented, including captive breeding programs and habitat restoration projects. 

So, aquarists around the world play a crucial role in these conservation efforts. 

Redtail Goodeid Behavior

The Redtail Goodeid is an active and social fish species with a range of interesting behaviors that make them a captivating addition to the home aquarium. 

They are gregarious by nature, which means they enjoy the company of their own kind. 

In the wild, they are often found in small shoals or groups, and this social behavior carries over to the aquarium setting.

While generally peaceful, Redtail Goodeids can exhibit territorial behavior, particularly among males. 

During breeding periods, males will compete for the attention of females and establish small territories within the aquarium. 

They are also active swimmers, often observed darting around the middle and lower areas of the tank. 

They may occasionally venture to the surface to feed, but they generally prefer the cover provided by dense vegetation and decorations. 

Redtail Goodeid Origin & Habitat

The Redtail Goodeid originates from the Mexican Pacific Slope, specifically in the states of Jalisco, Colima, and Michoacán. 

This region boasts a rich diversity of fish species, many of which are unique to this area. 

The Pacific Slope is characterized by a series of rivers and streams that flow from the western slopes of the Sierra Madre Occidental mountain range, eventually emptying into the Pacific Ocean.

In their natural habitat, Redtail Goodeids inhabit slow-moving freshwater streams and rivers, where the water is typically shallow and clear. 

These environments are often characterized by dense aquatic vegetation, submerged tree roots, and rocky substrates, which provide ample hiding spots and protection for the fish. 

The lush vegetation and organic matter in the water also support a diverse range of algae and invertebrates, which serve as the primary food source for the Redtail Goodeid.

The climate in the Mexican Pacific Slope is tropical to subtropical, with relatively stable temperatures throughout the year. 

The water temperature in their habitat typically ranges from 70-75°F (21-24°C), with a pH of around 7.0-8.0 and water hardness between 10-20 dGH.

What Are the Features of Redtail Goodeid?

1. Appearance

The Redtail Goodeid has an elongated, laterally compressed body that makes it easy for it to navigate its natural habitat of densely vegetated streams and rivers. 

Its large, overlapping scales give it a streamlined appearance, and its broad, slightly forked tail fin adds to its unique look.

One of the most exciting aspects of the Redtail Goodeid is its colorful tail. 

As you might guess from its name, this fish has a vibrant red tail fin that stands out and plays a role in attracting mates.

When it comes to coloration, it is a real showstopper, especially in males. 

They display a dazzling range of colors, including an iridescent blue sheen on their sides, a metallic green or turquoise hue on their back, and of course, the bright red or orange tail fin. 

The anal and dorsal fins often have black edges, which make the fish’s appearance even more striking.

Females, on the other hand, have a more subtle color palette. 

Their bodies are usually olive-brown or greenish-gray, with a row of dark blotches or spots running along their sides. 

While their tail fin is less vibrant than the males’, it may still show a hint of red. 

In addition, females are larger and more robust than males, which is a common trait among live-bearing fish species.

2. Body Size

Redtail Goodeids reach a length of about 2.5 to 3 inches (6.4 to 7.6 cm) when fully grown. 

But it’s worth noting that there is a size difference between the sexes, with females usually being larger and more robust than males.

This size difference between males and females is a common feature in live-bearing fish species. 

Females need extra space in their bodies to accommodate the developing fry during pregnancy. 

As a result, they tend to have a rounder, fuller body shape compared to the more streamlined, slender form of their male counterparts.

Redtail Goodeid Lifespan

The Redtail Goodeid has a relatively short lifespan compared to some other fish species of about 3 to 5 years

But this lifespan can be influenced by various factors, such as water quality, diet, tank conditions, and genetic factors.

For instance, a Redtail Goodeid with strong genetic traits may have a better chance of reaching the upper end of its lifespan range compared to those with weaker genetic traits.

Redtail Goodeid Life Cycle

1. Birth and Fry Stage

Redtail Goodeids are livebearing fish, which means the female gives birth to live, free-swimming fry rather than laying eggs. 

After a gestation period of approximately 8 weeks, the female releases the fry into the aquarium. 

The fry are fully formed and capable of swimming independently from the moment of birth. 

At this stage, they are quite small, measuring only a few millimeters in length.

2. Growth and Development

As the fry grow, they quickly begin to develop their distinct features. 

Within a few weeks, their bodies elongate, and their fins develop. 

They exhibit rapid growth during this stage, feeding on small live or powdered foods to fuel their development. 

So, it’s crucial to provide them with ample nutrition and a well-maintained environment to support their growth.

3. Juvenile Stage

After a few months, the fry transition into the juvenile stage. 

At this point, they resemble miniature versions of adult Redtail Goodeids. 

Their coloration starts to become more prominent, and their bodies continue to grow in length. 

But juvenile Redtail Goodeids are still sexually immature and unable to reproduce.

4. Sexual Maturity

Redtail Goodeids reach sexual maturity at around 3 to 4 months of age, depending on various factors such as genetics, growth rate, and environmental conditions. 

Once they have reached sexual maturity, males and females exhibit distinct physical characteristics and behaviors associated with courtship and reproduction.

5. Reproductive Behavior

Males court females through various displays, including vibrant coloration and fin displays. 

Once a female is receptive to mating, the male will position himself beside her, aligning his body with hers. 

Fertilization occurs internally, and the female carries the developing embryos within her body until birth. 

Redtail Goodeids are known for their ability to store sperm, allowing them to give birth to multiple batches of fry without subsequent mating.

6. Repeating the Cycle

After giving birth, the female will take a short period to recover before she becomes receptive to mating again. 

Redtail Goodeids can breed multiple times throughout their lives, usually at intervals of several weeks to a few months

This ability to reproduce in captivity has contributed to their popularity among breeders and aquarists.

Is Redtail Goodeid Hardy?

Redtail Goodeid is a hardy fish. They have the ability to adapt to a range of water conditions and are known to tolerate a variety of temperatures, pH levels, and water hardness. 

This resilience makes them suitable for beginner aquarists and those who may be less experienced in maintaining aquariums. 

However, it is still important to provide them with proper care, including a well-maintained tank environment, a suitable diet, and regular monitoring of water parameters to ensure their optimal health and well-being.

How to Care for Redtail Goodeid?

a.Water Requirements

1. Water Quality

Redtail Goodeids are hardy fish and capable of tolerating a range of water conditions, but it’s still essential to ensure that their living environment remains clean and safe. 

Poor water quality can lead to stress and illness, affecting not just the fish’s physical health, but also its behavior and coloration.

To ensure optimal water quality, it’s crucial to establish a consistent maintenance routine, including regular water changes. 

You should replace 25-50% of the tank water on a weekly basis, taking care not to disturb the substrate and the beneficial bacteria that help maintain a healthy aquatic environment. 

Removing excess food, waste, and decaying plant matter from the tank will also help prevent the build-up of harmful substances, such as ammonia, nitrites, and nitrates.

A reliable filtration system is indispensable in maintaining a healthy Redtail Goodeid tank. 

For this purpose, you should choose a filter that is appropriate for the size of your aquarium and provides both mechanical and biological filtration. 

Mechanical filtration helps remove solid particles, while biological filtration processes harmful substances like ammonia and nitrite through the action of beneficial bacteria. 

But you should know that it’s essential to clean or replace the filter media regularly to keep it functioning efficiently.

2. Water Temperature

These fish prefer a temperature range of 70°F to 75°F (21°C to 24°C), which closely mimics their natural habitat in the waters of Mexico. 

You can use a reliable aquarium heater and thermostat to achieve the ideal water temperature. 

The heater will maintain the desired temperature, while the thermostat will ensure that the temperature remains consistent, preventing fluctuations that could be harmful to your fish. 

It’s also important to invest in a high-quality aquarium thermometer to monitor the temperature in the tank regularly.

When selecting a heater, be sure to choose one with an appropriate wattage for the size of your aquarium. 

For instance, if you have a 20-gallon tank, a heater with a power output of around 100 watts should suffice. 

The placement of the heater in the tank is another consideration. Position it in an area with good water flow, as this will help distribute the heat evenly throughout the aquarium. 

But avoid placing the heater too close to decorations or plants, as this could cause overheating or create hotspots.

It’s worth noting that the ambient temperature in your home can also impact the water temperature in your Redtail Goodeid tank. 

In colder months, you may need to increase the heater’s power slightly to maintain the optimal temperature range. 

Conversely, in warmer weather, you might want to monitor the temperature more closely to ensure it doesn’t rise too high. 

In extreme cases, you might need to consider using an aquarium chiller to keep the temperature within the preferred range.

3. pH Level

The pH value measures the acidity or alkalinity of the water, and maintaining an appropriate range is important for the health of your fish. 

Redtail Goodeids are adaptable and can tolerate a pH range of 7.0 to 8.0, which is roughly neutral to slightly alkaline.

You might wonder why the pH level matters so much. 

Well, water’s pH can affect various biological processes, such as the efficiency of the fish’s gills to absorb oxygen and release carbon dioxide, the health of their skin, and their ability to fight off infections. 

A sudden change in pH can also be extremely stressful for fish and may lead to severe health issues.

So, testing the pH level in your aquarium regularly is therefore of utmost importance. 

There are several easy-to-use aquarium test kits available in pet stores and online that can measure pH. 

It’s also a good idea to test the pH once a week, or any time you notice unusual behavior in your fish that might suggest they are under stress.

If the pH level in your aquarium is not within the appropriate range for Redtail Goodeids, you can adjust it using aquarium-safe products. 

To raise the pH level (make the water more alkaline), you can use a commercial pH increaser or add a buffering agent like crushed coral, limestone, or aragonite to the substrate or filter. 

These materials release calcium and carbonate ions, which can help raise the pH level. 

If you need to lower the pH level (make the water more acidic), you can use natural methods like adding peat moss or driftwood to your aquarium. 

These materials release tannins and other organic compounds that can reduce the pH. 

But keep in mind that it’s essential to make changes gradually and consistently monitor the pH level.

4. Water Hardness

Water hardness refers to the concentration of dissolved minerals, primarily calcium and magnesium, in the water. 

It plays an essential role in maintaining the well-being of aquatic organisms, including Redtail Goodeids. 

These fish prefer moderately hard water with a general hardness (GH) of 10-20°dGH (degrees of general hardness). 

To test the water hardness in your aquarium, you can purchase test kits from pet stores or online that measure general hardness. 

It’s a good practice to test the hardness every couple of weeks or whenever you observe changes in the behavior or appearance of your fish that might indicate discomfort or stress.

If you find that your aquarium’s water hardness is too low (soft water), you can increase it using commercial water hardness buffers or by adding crushed coral, limestone, or aragonite to the substrate or filter. 

These materials slowly release calcium and magnesium ions into the water, raising the general hardness. 

If the water hardness is too high (hard water), you can lower it by mixing your tap water with purified water, such as reverse osmosis (RO) or distilled water. 

These types of water have a low mineral content and can help dilute the high concentration of minerals in your tap water. 

b.Tank Requirements

1. Tank Size

Choosing the appropriate size is crucial for the health and happiness of your fish, as it provides them with adequate space to swim, explore, and establish territories. 

Additionally, a properly-sized tank can help maintain stable water conditions, such as temperature and water quality.

Redtail Goodeids are small to medium-sized fish, typically growing to around 2.5 to 3 inches (6.4 to 7.6 cm) in length. 

Considering their adult size, a minimum tank size of 20 gallons (76 liters) is ideal for a small group of these fish. 

A larger tank of 30 gallons (114 liters) or more is even better, as it will provide more swimming space and help further maintain stable water conditions.

When selecting a tank for your Redtail Goodeids, you should also consider the tank’s dimensions. 

These fish prefer a tank with a larger footprint, meaning that it is longer and wider rather than taller. 

A long and wide tank provides more surface area for swimming and offers multiple hiding spots, which can help reduce stress and territorial aggression.

If you plan on keeping Redtail Goodeids with other species in a community tank, be mindful that the tank’s size should be increased accordingly. 

The general rule of thumb is to allocate one gallon (3.8 liters) of water for every inch (2.54 cm) of fish, but this rule can vary depending on the specific requirements of the fish species you’re planning to keep together.

You should also know that a larger tank is not just beneficial for the fish but also for the aquarist. 

A larger volume of water is more forgiving when it comes to maintaining water quality and parameters, as it can better dilute waste products and is less prone to rapid fluctuations in temperature and other conditions.

2. Decorations

Decorations play an important role in creating a visually appealing and comfortable environment for your Redtail Goodeids. 

By carefully selecting and arranging the decorations, you can replicate their natural habitat, provide them with shelter and hiding spots, and enhance their overall well-being. 

There are various types of decorations suitable for a Redtail Goodeid aquarium, and incorporating a combination of these elements will create a diverse and interesting environment for your fish.

For example, live plants are an excellent addition to a Redtail Goodeid tank. 

These fish come from habitats with plenty of vegetation, so including plants in their aquarium helps mimic their natural environment. 

Live plants, such as Java fern, Anubias, Vallisneria, and Amazon sword, not only provide shelter and hiding spots but also contribute to the overall water quality by absorbing nitrates and releasing oxygen. 

Driftwood is another attractive and functional decoration option for a Redtail Goodeid aquarium. 

The addition of driftwood can create a natural and visually appealing environment while providing your fish with hiding spots and shelter. 

It’s important to choose driftwood that has been properly treated and is aquarium-safe, as untreated driftwood can leach harmful substances into the water. 

Additionally, bear in mind that driftwood can lower the pH of the water and affect the water hardness, so it’s essential to monitor these parameters closely.

You can also add rocks and stones to create interesting structures and hiding spots in a Redtail Goodeid tank. 

But choose smooth, aquarium-safe rocks, such as river rocks, slate, or lava rocks, to create caves or small territories for your fish. 

However, keep in mind that some rocks, like limestone or Texas holey rock, can raise the water hardness and pH, so test your water parameters regularly if you include these in your aquarium.

3. Lighting

Just like us, Redtail Goodeids require a specific lighting schedule to mimic the natural day and night cycles they would experience in their native habitat. 

They need moderate lighting in their aquarium. 

Too bright light can stress these fish and lead to excessive algae growth in the tank, while too dim light can inhibit their natural behavior and coloration.

You can achieve this optimal lighting condition by using a dedicated aquarium light. 

LED lights are an excellent choice for Redtail Goodeid tanks, as they offer adjustable brightness and can be set to mimic the natural progression of daylight. 

You can also select lights that cater to the needs of live plants if you’ve chosen to include these in your aquarium setup.

A standard lighting schedule for these buddies is about 8-10 hours of light per day, simulating a typical daylight cycle. 

You can easily manage this with the help of a timer, ensuring consistency for your fish. 

This schedule not only encourages the active behavior of your fish during “the daytime” but also allows them to rest during the “nighttime” without being stressed by constant light.

Redtail Goodeid Compatibility

Redtail Goodeids are generally peaceful and social fish that can coexist with a variety of other community tank species. 

However, it’s essential to consider their compatibility with other fish to ensure a harmonious and stress-free environment. 

Here is a detailed breakdown of good and bad tank mates for Redtail Goodeids:

Good Tank MatesBad Tank Mates
GuppiesAggressive Cichlids
SwordtailsFin-nipping Tetras
MolliesNippy Barbs
PlatiesBoisterous Goldfish
DaniosAggressive Bettas
RasborasPredatory Fish (e.g., Oscars)
Corydoras CatfishLarge and Aggressive Catfish
Dwarf GouramisPufferfish
White Cloud Mountain MinnowsAfrican Cichlids

Redtail Goodeid Diet & Feeding

Redtail Goodeids have an omnivorous diet, which consists of various food sources in their natural habitat. 

In the wild, they feed on algae that grow on rocks, plants, and other surfaces. 

They also consume small invertebrates like insect larvae, worms, and crustaceans.

 Additionally, they scavenge on detritus, which is decomposing organic matter present in the water. 

This diverse diet provides them with the necessary nutrients for growth and reproduction.

To replicate their natural diet in captivity, it’s important to provide a well-balanced and varied feeding schedule. This diet can include: 

  • High-quality flake food
  • Pellet food
  • Brine shrimp
  • Daphnia
  • Spirulina flakes
  • Bloodworms

You should also feed them small portions that can be consumed within a few minutes to prevent overfeeding and maintain good water quality. 

Here’s a sample feeding schedule for Redtail Goodeids throughout the week that I already use:

MondayHigh-quality flake food
TuesdayLive or frozen brine shrimp
WednesdayPellet food
FridayVegetable-based food (e.g., spirulina flakes)
SundayFasting day (no feeding)

Redtail Goodeid Breeding

Redtail Goodeids are special because they give birth to live, free-swimming fry instead of laying eggs. 

It all starts with the courtship displays of the male Goodeids, who put on a vibrant show of colors, fin displays, and energetic swimming patterns to catch the attention of the females. 

It’s like a dance of love that sets the stage for reproductive magic to happen.

When a female Goodeid is ready to mate, she positions herself near the male, aligning her body parallel to his. 

It’s a beautiful connection, allowing the transfer of sperm from the male to the female using a specialized fin called a gonopodium. 

This intimate moment of fertilization takes place internally, and the female can store the sperm to fertilize multiple batches of fry over time. 

It’s nature’s way of ensuring future generations.

During the following 8 weeks, something incredible happens inside the female Goodeid’s body. 

The new mommy carries the developing embryos, nurturing them with a special yolk sac. 

It’s like a cozy home where the tiny lives take shape. 

To support this important stage, you should provide the pregnant female with a stress-free environment, plenty of hiding spots, and a well-balanced diet. Think of it as pampering the mom-to-be.

And then, the magic moment arrives. The female gives birth to live, free-swimming fry. 

It’s an awe-inspiring sight to see these little ones enter the world, fully formed and ready to explore their new surroundings. They are like tiny sparks of life, adding joy and wonder to your aquarium.

Now, here comes the important part: ensuring the safety of the fry. 

Redtail Goodeids don’t show strong parental care, so you need to separate the fry from the adults to prevent predation. 

You can provide a separate nursery tank or create hiding spots within the main tank, like lush vegetation or mesh breeding traps, which will give the fry a safe haven to grow and thrive. 

And don’t forget to nourish them with specialized fry food, crushed flakes, or infusoria to support their healthy development. It’s like giving them a nutritious feast to fuel their growth.

Redtail Goodeid Common Diseases

Redtail Goodeids are generally hardy fish, but they can still be susceptible to certain diseases. 

Being aware of common diseases that may affect them is essential for maintaining their health and well-being. 

Here are some common diseases that can affect these guys, along with their symptoms, causes, treatment, and prevention measures.

Ichthyophthiriasis (Ich)White spots resembling grains of salt on the fish’s body and finsCaused by the parasite Ichthyophthirius multifiliisMedications like copper-based treatments or malachite greenQuarantine new fish before introducing them to the main tank. Maintain good water quality and optimal tank conditions. Avoid overcrowding
Fin RotFins appear ragged, frayed or erodedBacterial infection, often resulting from poor water conditions or stressAntibacterial medications, along with improving water qualityMaintain a clean and well-maintained aquarium. Ensure proper water parameters and reduce stress factors
Swim Bladder DisorderFish have difficulty maintaining buoyancy, may float or sink uncontrollablyCan be caused by bacterial infection, injury, or genetic factorsImproving water quality, providing a varied and balanced dietMaintain proper water conditions, avoid overfeeding, and ensure a varied diet
Fungal InfectionsCotton-like growths on the fish’s body or finsCaused by various fungal pathogensAntifungal medications, along with improving water qualityMaintain a clean and well-maintained aquarium. Avoid stressors and ensure good water quality
DropsySwollen abdomen scales sticking out like a pineconeBacterial infection, often related to poor water conditions or internal organ failureAntibiotics, improving water quality, isolating affected fishMaintain good water quality, provide a balanced diet, and avoid overfeeding. Quarantine sick fish to prevent the spread of infection
Velvet DiseaseYellowish-gold or dusty appearance on the fish’s skinCaused by the parasite Piscinoodinium pillulareMedications like copper-based treatments or formalinQuarantine new fish before introducing them to the main tank. Maintain good water quality and optimal tank conditions


How Often Should I Feed My Redtail Goodeids?

You should feed your Redtail Goodeids two to three times per day, offering small portions of food each time. 

Feeding them in smaller amounts more frequently can help prevent overfeeding and keep the water quality in check.

Can Redtail Goodeids Live with Other Fish Species in a Community Tank?

Redtail Goodeids can live with other peaceful, similarly-sized fish species in a community tank. 

However, it’s essential to ensure that the tank is large enough and has plenty of hiding spots to avoid territorial disputes and stress.

How Do I Know If My Redtail Goodeid Is Healthy?

You know if Redtail Goodeid is healthy when it exhibits vibrant colors, active swimming behavior, and a good appetite. 

Signs of illness may include lethargy, loss of appetite, discolored or damaged scales, and erratic swimming behavior. 

If you suspect your fish is unwell, consult an aquatic veterinarian or a specialist at your local fish store for advice.

Do Redtail Goodeids Require a Specific Water Flow in Their Tank?

Redtail Goodeids require a moderate water flow in their tank, as they naturally inhabit flowing water habitats. 

A gentle water flow can be achieved with the use of a suitable filter or powerhead, which also helps in maintaining good water quality and oxygen levels.


As promised, we’ve covered the essential aspects of Redtail Goodeid care, exploring their water requirements, tank setup, and various factors that contribute to their well-being.

Just remember, maintaining a healthy habitat for your buddies requires ongoing attention and care, but with dedication and a little effort, you’ll be rewarded with a fascinating underwater world that both you and your fish will enjoy.

Do you still have questions? If so, leave a comment and I’ll be happy to answer them.

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