Filament Barb, Black-Spot Barb (Puntius filamentosus (syn. Barbus filamentosus)) — 5-6cm

Overview

The Filament Barb (Puntius filamentosus, syn. Barbus filamentosus), also known as the Black-Spot Barb, is a striking South Indian cyprinid celebrated for its elongated, flowing fins and lively shoaling behavior. Native to the rivers and streams of the Western Ghats, this medium-sized barb can reach up to 10cm in length and brings both movement and visual interest to larger community aquariums. The species is named for the long, thread-like extensions that develop on the dorsal and anal fins of mature males, creating an elegant silhouette that is particularly impressive in well-maintained groups. Peaceful and adaptable, the Filament Barb is available for sale UK-wide and is well-suited to aquarists with moderate experience seeking a robust, active species for planted or biotope setups. Its moderate care requirements and compatibility with a wide range of peaceful tankmates make it a rewarding addition to freshwater collections.

Appearance

Puntius filamentosus is a beautifully proportioned barb with a streamlined, laterally compressed body and large, expressive eyes. The base coloration is a soft silver-gold, often with subtle greenish or bronze reflections depending on lighting and water conditions. A distinctive black spot is usually present near the caudal peduncle, giving rise to the common name Black-Spot Barb. The most striking feature is the elongated filamentous rays that extend from the dorsal and anal fins of mature males, which can reach impressive lengths and trail gracefully behind the fish as it swims. Females are generally fuller-bodied, especially when gravid, and lack the extended fin rays. The fins may show hints of orange, red, or yellow, particularly during breeding periods or when the fish is well-conditioned. Juveniles are less colorful and lack the filaments, but these develop gradually as the fish matures.

Natural Habitat

Puntius filamentosus is endemic to South India, particularly the river systems of the Western Ghats, a biodiversity hotspot known for its rich aquatic fauna. The species inhabits clear, fast-flowing streams and rivers with rocky substrates, well-oxygenated water, and abundant aquatic and riparian vegetation. During the monsoon season, water levels rise significantly, and the fish may migrate into flooded areas and side channels where food is plentiful. The natural environment is characterized by moderate to strong current, slightly acidic to neutral pH, and soft to moderately hard water. The Filament Barb feeds on insects, larvae, algae, and detritus in the wild, and is typically found in small shoals that move together through the mid-water column, taking advantage of the flow to intercept food particles. Replicating these conditions in captivity—clean, well-oxygenated water, moderate flow, and plenty of swimming space—helps the species thrive and display its natural behavior.

Aquarium Setup

A minimum tank size of 100 litres is recommended for a small group of Filament Barbs, though larger aquariums of 150 litres or more are preferable for a proper shoal and additional tankmates. The aquarium should feature robust filtration and moderate water flow to simulate the species' natural riverine habitat and ensure good oxygenation. A substrate of smooth river stones, fine gravel, or sand works well, and the tank should be decorated with driftwood, smooth rocks, and hardy plants such as Java Fern, Anubias, Bolbitis, and Vallisneria to provide cover and create natural swimming lanes. Open areas in the center of the tank allow the barbs to display their active, schooling behavior and showcase their impressive finnage. Lighting should be moderate to bright, as this helps bring out the fish's coloration and supports plant growth. A well-fitted lid or cover glass is essential, as barbs are active and may jump when startled. Regular maintenance, including weekly water changes of 25-30%, is crucial to maintain water quality and prevent the buildup of organic waste.

Water Parameters

Puntius filamentosus thrives in clean, well-oxygenated water with a temperature range of 24-28°C, reflecting its tropical South Indian origins. The pH should be maintained between 6.5 and 7.5, with soft to moderately hard water (GH 5-12°dGH) preferred. Good filtration, surface agitation, and regular water changes are essential to keep ammonia and nitrite at zero and nitrate below 20ppm. The species is moderately sensitive to poor water quality and will show stress through lethargy, loss of appetite, or fin clamping if conditions deteriorate. Avoid sudden changes in temperature or chemistry, and use a reliable heater and thermometer to maintain stable conditions year-round. Test water parameters regularly, especially after stocking new fish or during periods of high feeding, to ensure the aquarium remains within the species' preferred range. Providing consistent, high-quality water conditions supports long-term health, vibrant coloration, and the development of the males' characteristic filaments.

Feeding

Filament Barbs are omnivorous and accept a wide variety of foods in the aquarium. A high-quality flake or micro-pellet food should form the staple diet, supplemented regularly with frozen or live foods such as daphnia, brine shrimp, bloodworms, and mosquito larvae. These protein-rich foods help maintain condition, enhance coloration, and encourage the development of the males' filamentous fins. Occasional vegetable matter, such as blanched spinach, spirulina flakes, or algae wafers, provides dietary fiber and supports digestive health. Feed small amounts two to three times daily, offering only what the fish can consume within a few minutes to prevent overfeeding and maintain water quality. In a well-planted tank, the barbs will also graze on biofilm and microorganisms growing on plant leaves and surfaces. Varied feeding not only keeps the fish healthy but also stimulates their natural foraging instincts and ensures balanced nutrition for long-term vitality.

Behaviour

Puntius filamentosus is a peaceful, active schooling species that spends most of its time in the mid-water levels of the aquarium. When kept in proper groups, the fish exhibit confident, natural behavior, swimming together in loose formations and exploring all areas of the tank. The males may engage in mild displays and posturing, particularly during breeding periods, but these interactions rarely result in injury and are part of the species' normal social structure. Solitary or poorly grouped individuals often become shy, hide frequently, and may show reduced activity and coloration. The Filament Barb is generally non-aggressive and will not harass other tankmates, making it an excellent choice for peaceful community setups. During feeding times, the shoal becomes more animated, darting quickly to intercept food particles and displaying impressive coordination. Provide plenty of swimming space and avoid overcrowding, as cramped conditions can lead to stress and increased susceptibility to disease.

Tank Mates

The Filament Barb's peaceful nature and moderate size make it compatible with a wide range of similarly sized, non-aggressive community species. Ideal tankmates include other peaceful barbs, danios, rasboras, rainbowfish, and peaceful tetras such as Congo or Black Phantom Tetras. Bottom-dwellers like Corydoras catfish, larger loaches, and peaceful cichlids such as Kribensis can also coexist peacefully. Avoid housing them with large aggressive cichlids, fin-nipping species, or very slow-moving long-finned fish such as Bettas and fancy Guppies. Very small fry or dwarf shrimp may occasionally be eaten, so avoid mixing with delicate invertebrates if breeding is a concern. When selecting tankmates, prioritize species with similar water parameter requirements and peaceful temperaments to create a harmonious, stress-free community environment. The Filament Barb's active swimming and impressive finnage make it a standout species in larger, well-planted aquariums.

Breeding

Breeding Puntius filamentosus in the home aquarium is possible with proper preparation and attention to detail. Like most cyprinids, this species is an egg-scatterer, releasing adhesive eggs among fine-leaved plants or spawning mops. A separate breeding tank of 60-100 litres with soft, slightly acidic water (pH 6.0-6.5) and a temperature around 26-27°C is recommended. Condition the breeding group with high-quality live and frozen foods for 2-3 weeks before introducing them to the spawning setup. Spawning typically occurs in the early morning, with the female releasing eggs that are immediately fertilized by the male. Remove the adults promptly after spawning, as they will readily consume their own eggs and fry. The eggs hatch within 24-48 hours, and the fry become free-swimming after another 3-4 days. Feed the fry infusoria or liquid fry food initially, progressing to newly hatched brine shrimp and finely crushed flake food as they grow. Maintain excellent water quality and perform small, frequent water changes to support healthy fry development.

Why Buy from Tropical Fish Co

At Tropical Fish Co, we specialize in supplying healthy, acclimatized freshwater species from trusted suppliers across the UK. Our Filament Barbs are quarantined, carefully inspected, and conditioned to ensure they arrive in peak health and ready to thrive in your aquarium. We provide expert guidance on stocking, compatibility, and care requirements, helping you build a balanced, vibrant community tank. All fish are packed with care using insulated boxes and heat packs (when required) to ensure safe delivery. With decades of combined experience in the hobby, our team is here to support you every step of the way, from choosing the right species to ongoing advice on husbandry and maintenance. Whether you're a beginner or an experienced aquarist, Tropical Fish Co is your trusted partner for quality livestock and outstanding customer service.