Parosphromenus filamentosus – Parosphromenus filamentosus

Among labyrinth fish lovers, few species are as captivating and understated as Parosphromenus filamentosus. This tiny jewel from Asian blackwater forests is both delicate and rewarding, especially for aquarists who enjoy recreating natural habitats and observing subtle behavior. In this article, we will explore its origins, care requirements, breeding, and how to equip an ideal tank, with solutions available from MB Store’s range of aquariums and aquarium equipment.

Origin and natural habitat of Parosphromenus filamentosus

Parosphromenus filamentosus belongs to the genus Parosphromenus, commonly known as licorice gouramis. These fish inhabit peat swamp forests and slow-moving blackwater streams in Southeast Asia, particularly in Borneo and surrounding regions. Their natural waters are extraordinarily soft, acidic, and tinted a dark tea color due to humic substances released from decaying leaves and peat.

In the wild, these fish live among submerged roots, fallen leaves, and dense marginal vegetation. Light hardly penetrates the water surface, so the fish are adapted to dim environments where visual communication relies on iridescent colors that shimmer when the males display to rivals or potential mates. The environment is poor in minerals but rich in organic matter, with almost no current.

Understanding this habitat is crucial when designing an aquarium. Successful care of Parosphromenus species depends less on size and more on water quality, structure, and stability. These fish are not general community fish; they thrive when their specialized requirements are respected. Fortunately, with appropriate filtration, lighting, and careful selection of water-conditioning materials, it is possible to approximate their natural environment at home.

Aquarium setup: dimensions, layout and essential equipment

For a dedicated pair or trio of Parosphromenus filamentosus, a relatively small aquarium can be sufficient, for example 30–40 liters. However, “small” does not mean “simplistic”. They need a stable, mature system with carefully chosen equipment. MB Store offers a wide selection of aquariums, as well as filters, heaters, and lighting suitable for sensitive species like this.

Because these fish are shy and prefer calm water, choose a filter that provides gentle flow, such as a small internal filter with adjustable output or an external canister with a spray bar directed at the glass. Sponge filters powered by air pumps are another excellent choice; they offer biological filtration and very little current. The objective is to keep the water clean without creating strong turbulence.

As for layout, a biotope-inspired arrangement will help the fish display natural behavior:

• Dark substrate: fine sand or a thin layer of inert gravel helps highlight the colors and supports leaf litter.
• Leaf litter: Indian almond leaves, oak, beech or catappa create a natural look and release tannins, which slightly tint the water and provide hiding spots.
• Roots and branches: thin driftwood or branches simulate submerged roots and add visual barriers important for territorial males.
• Caves and micro-shelters: small pieces of half coconut shells, ceramic tubes, or leaf cones provide crucial egg-laying and retreat sites.

Lighting should be soft and subdued. Intense illumination will stress the fish and discourage natural behavior. Floating plants like Salvinia, frogbit, or Pistia are ideal to block excess light and provide a sense of security, while also helping with nutrient uptake. MB Store offers a variety of LED units with dimming options, making it easy to achieve this gentle lighting.

Water parameters, blackwater conditions and maintenance

The most critical aspect of keeping Parosphromenus filamentosus is water quality. In their natural habitat, conductivity is extremely low, with hardly any dissolved minerals. pH values often fall between 4.0 and 6.0. While not every aquarist will aim for such extremes, approaching them significantly improves health and breeding success.

Recommended basic water parameters for this species are:

• Temperature: 24–27 °C
• pH: 4.5–6.5, with 5.0–5.8 often giving the best results
• GH: 0–3 °d
• KH: close to 0, to allow stable low pH
• Conductivity: typically 20–80 µS/cm for dedicated breeders

Achieving such water values usually requires the use of reverse osmosis (RO) or deionized water mixed with a very small amount of tap water, or a specialized mineral supplement designed for soft-water fish. Peat granules, catappa leaves, alder cones and other botanical materials may be used to lower pH and create a true blackwater environment. MB Store offers RO units, test kits and additives to help monitor and stabilize conditions.

Maintenance must be cautious. Large, abrupt water changes can shock the fish, particularly if the new water differs in temperature or mineral content. Instead, perform smaller, regular changes of around 10–20% per week, using pre-conditioned water with matching temperature and chemistry. Vacuum the substrate only lightly, because leaf litter and biofilm are part of the natural microhabitat and serve as an important source of microorganisms and shelter for fry.

Filtration materials should favor biological stability. Porous ceramic media or sponges are preferable to aggressive chemical resins that strip the water of humic substances. Activated carbon can remove beneficial tannins, so if used, it should be applied briefly and selectively. By monitoring pH, conductivity and nitrogen compounds (ammonia, nitrite, nitrate) with reliable test kits, the aquarist can detect issues early and respond before the fish show stress.

Behavior, social structure and compatibility

Parosphromenus filamentosus is a small, peaceful but somewhat territorial labyrinth fish. Males develop elongated filamentous fin extensions and stronger coloration, especially when displaying. The species is typically kept as pairs or small harems in species-only setups. In such conditions, the fish reveal an impressive range of courtship behaviors and subtle signals.

Unlike larger gouramis, Parosphromenus species are not well suited to typical community aquariums. Their small size, timid nature and preference for very soft, acidic water make them vulnerable when kept with robust or fast-moving tankmates. Even seemingly peaceful nano-fish can outcompete them for food or cause stress simply by being more active.

If companions are considered at all, they should be carefully chosen. Tiny, calm blackwater-adapted species such as certain Boraras or Sundadanio may work in larger setups, but for most aquarists, the best solution is a dedicated aquarium. This allows for precise feeding, observation of breeding behavior and stricter control of water parameters.

Thanks to their labyrinth organ, these gouramis can breathe atmospheric air, allowing them to cope with low-oxygen habitats. Still, this does not mean that poor water quality is acceptable; high nitrite or ammonia levels will be just as harmful as for any other fish. Provide easy access to the water surface and avoid covering the aquarium so tightly that the air layer becomes cold or stagnant. A hood or cover glass that keeps humidity and temperature stable above the water is ideal.

Feeding Parosphromenus filamentosus: live and frozen foods

Feeding is another challenging aspect of caring for Parosphromenus species. In nature, they feed primarily on tiny aquatic invertebrates such as insect larvae, crustaceans and other microfauna. Many individuals are reluctant to accept dry foods, especially newly imported wild fish.

A varied diet based on high-quality live and frozen foods is strongly recommended. Suitable items include:

• Live baby brine shrimp (Artemia nauplii)
• Microworms and grindal worms
• Daphnia and Moina
• Blackworms or small bloodworms (in moderation)
• Frozen cyclops and Artemia

Live foods not only match the natural diet but also stimulate hunting behavior and enhance coloration. Over time, some specimens can be trained to accept soft, high-protein prepared foods, but this should be seen as a complement rather than the main staple. Uneaten food quickly pollutes soft, warm water, so feed in small portions and observe that all fish are eating.

When conditioning breeders, offer several small meals per day. High-quality nutrition is essential not only for successful spawning but also for the development of strong, healthy fry. MB Store carries a wide selection of frozen foods and tools for culturing live food at home, such as Artemia hatcheries and breeding containers, making it easier to maintain a consistent supply.

Breeding Parosphromenus filamentosus in the aquarium

One of the major attractions of keeping Parosphromenus filamentosus is the opportunity to observe their courtship and parental care. These fish are cave spawners. The male chooses a small sheltered cavity—often under a leaf, inside a narrow tube or beneath a root—and prepares it as a spawning site. He then entices the female with displays involving body postures, fin flaring and intensified coloration.

To encourage breeding, provide several potential caves of different sizes and shapes. Half coconut shells, ceramic tubes, or small leaf cones are especially appreciated. Ensure that the entrance is tight enough to make the fish feel safe but large enough for the pair to enter. Soft, acidic water and a calm environment are key; frequent disturbances or sudden changes in parameters can interrupt breeding attempts.

When a female is ready, she will follow the male into the cave where the pair embrace and release eggs and sperm. The eggs, often attached to the cave ceiling or wall, are then guarded mainly by the male. He fans them with his fins to ensure proper oxygenation and may repair the structure or chase away intruders. During this period, it is important not to disturb the aquarium excessively.

After hatching, the fry remain in or near the cave for several days until their yolk sacs are absorbed and they begin to swim freely. At that point, they require very fine food, such as infusoria, vinegar eels, paramecia or specially prepared powdered fry diets. As they grow, they can move on to freshly hatched Artemia and microworms. Fine-pored sponge filters and gentle surface flow protect the fry from being sucked into equipment or exhausted by currents.

Some breeders choose to remove the parents once the fry are free-swimming to avoid the risk of predation, while others report that parental fish sometimes tolerate their offspring. Observation and experience will guide which approach works best in a given setup. A separate small grow-out tank with similar water parameters is often a good idea to maximize survival.

Choosing equipment and supplies from MB Store

Creating a stable, species-appropriate environment for Parosphromenus filamentosus requires thoughtful equipment choices. MB Store offers a wide range of aquariums and aquarium equipment that can be tailored to the needs of soft-water blackwater species. When planning a setup, consider the following categories:

• Aquariums: Opt for compact models with good viewing panels and secure covers to maintain warm, humid air above the surface.
• Filtration: Gentle internal filters, sponge filters and low-flow external filters with adjustable outputs are ideal.
• Heating: Reliable, adjustable heaters maintain stable temperatures in the preferred range.
• Lighting: Dimmable LED systems support subdued lighting and the growth of floating plants.
• Water treatment: RO units, conditioners, peat and botanicals help create authentic blackwater conditions.
• Testing: Accurate test kits for pH, GH, KH, conductivity and nitrogen compounds are essential for monitoring.

By selecting compatible components from MB Store, aquarists can assemble a system that emphasizes stability, low stress and natural behavior. This approach benefits not only Parosphromenus species but also many other soft-water fish, from dwarf cichlids to delicate tetras. Investing in quality equipment reduces long-term problems and offers greater satisfaction when the fish thrive and display their full beauty.

Is Parosphromenus filamentosus right for you?

Parosphromenus filamentosus is not a beginner’s fish, yet it is not impossible to keep for dedicated aquarists ready to learn and adapt. The species demands consistent water conditions, high-quality soft water, regular (but gentle) maintenance, and access to suitable live and frozen foods. In return, it offers fascinating social interactions, intricate courtship and the satisfaction of supporting a rare and often threatened group of fish.

Before acquiring this species, ask yourself whether you can provide:

• Access to RO or very soft water
• Time to culture or purchase appropriate foods
• A quiet, species-only or very carefully planned aquarium
• Patience to observe subtle behavior and gradual acclimation

If the answer is yes, then Parosphromenus filamentosus can become a centerpiece of a carefully curated blackwater setup. For many enthusiasts, caring for these fish also carries a conservation dimension, as peat swamp habitats are under severe pressure from development and climate change. Maintaining and breeding the species in captivity may contribute to preserving its genetic diversity.

With thoughtfully selected aquarium systems and accessories from MB Store, even demanding species like this can be maintained with relative confidence. Combining sound technical support, quality equipment and a deep interest in natural history, aquarists can turn a small glass box into a genuine refuge for one of the aquarium world’s most enchanting small gouramis.

FAQ – Parosphromenus filamentosus

How large does Parosphromenus filamentosus grow?
Adult Parosphromenus filamentosus typically reach about 3–4 cm in length, making them true nano-fish. Despite their small size, they require carefully maintained conditions and do best in species-only setups where their subtle behavior can be observed without competition or harassment from larger tankmates.

Can Parosphromenus filamentosus live in a community aquarium?
They are not ideal for standard community aquariums. Their need for very soft, acidic water and their timid nature make them vulnerable in mixed setups. Active or larger fish will often outcompete them for food. A dedicated species tank or one with a few extremely peaceful nano-fish in similar water is far safer.

Do I need blackwater to keep this species?
While they may survive in slightly different conditions, authentic blackwater with low hardness and acidic pH significantly improves health, coloration and breeding success. Using RO water, botanicals and gentle filtration helps create these conditions. Stable parameters are more important than chasing extreme values without proper control.

What should I feed Parosphromenus filamentosus?
Offer a diet based mainly on small live and frozen foods, such as Artemia nauplii, microworms, Daphnia and cyclops. Many specimens ignore dry flakes and pellets, especially at first. Feed modest portions several times daily, remove uneaten food promptly and observe that each fish is eating adequately.

Is breeding Parosphromenus filamentosus difficult?
Breeding is achievable if you provide soft, acidic water, caves for spawning and high-quality live foods. The male usually guards eggs and early fry. Very small foods like infusoria are required when fry become free-swimming. Stability and patience are vital, but once conditions are right, pairs may spawn regularly.