Brown Rivulus, Green Rivulus (Rivulus cylindraceus) — 3-4cm

Overview

The Brown Rivulus or Green Rivulus (Rivulus cylindraceus) is a small, attractive Cuban rivulus native to Cuba and nearby Caribbean freshwater habitats. Reaching 4cm in length, this peaceful species is prized for its subtle brown-green coloration and fascinating behavior. Ideal for a quiet planted nano aquarium, Rivulus cylindraceus thrives in soft, slightly acidic water with gentle filtration. Available for sale UK from Tropical Fish Co, this captivating killifish rewards dedicated keepers with unique surface-dwelling behaviour and delicate beauty.

Appearance and Coloration

The Brown Rivulus displays subtle but attractive colouration with a slender, cylindrical body adorned in earthy brown-green tones with delicate iridescence. Males are more intensely coloured than females, with more pronounced finnage and faint green highlights that shimmer under subdued lighting. Females are smaller, plumper, and more subdued in colour. The overall appearance is modest but elegant, perfectly suited to a natural planted aquarium. In a tank with dark substrate and tannin-stained water, the subtle green highlights become more visible.

Natural Habitat

Rivulus cylindraceus is native to Cuba and nearby Caribbean freshwater habitats, where it inhabits slow-moving streams, swamps, ditches, and seasonal pools. These waters are typically soft, slightly acidic to neutral, and well-vegetated, with a substrate of mud, sand, and organic debris. Water flow is minimal, and the habitat provides abundant surface cover from floating plants and overhanging vegetation. These fish are surface-oriented and may tolerate brief air access, a characteristic adaptation of rivulid killifish.

Aquarium Setup

A minimum 20-litre aquarium is sufficient for a pair or small group of Brown Rivulus. Use a fine sand or smooth gravel substrate with plenty of live plants such as Cryptocoryne, Java moss, Microsorum, and floating species like Salvinia or Pistia. Provide open swimming space near the surface, as this is a surface-oriented species. Add dried leaves (Indian almond or oak) to release tannins and replicate the natural environment. Lighting should be subdued, and filtration gentle to avoid strong currents. A secure, tight-fitting lid is essential, as rivulids can jump and may tolerate brief air access.

Feeding and Diet

As a carnivore, Rivulus cylindraceus requires a varied small meaty diet to maintain health and colour. Offer a varied diet including live or frozen bloodworms, daphnia, brine shrimp, mosquito larvae, and quality micro-pellets daily. Occasional small insect prey is beneficial. This surface-oriented predator is well-adapted to capturing small prey at the water's surface. Feed small portions once or twice daily, removing uneaten food promptly to maintain water quality.

Behaviour and Temperament

The Brown Rivulus is a peaceful, surface-dwelling species that spends most of its time patrolling the upper water column in search of food. Males may display to each other with flared fins and subtle posturing, but serious aggression is rare. These fish are most active during dawn and dusk, and they appreciate a dimly lit aquarium with plenty of surface cover. They are not competitive feeders, so avoid housing them with boisterous or fast-moving species.

Suitable Tank Mates

Rivulus cylindraceus is best kept singly or as a pair/species-only setup. If tankmates are used, only very small, peaceful species with similar water needs should be considered. Avoid large predatory fish, fast boisterous fish, fin-nippers, aggressive cichlids, and large crayfish or predatory invertebrates. A calm, quiet environment is essential for this delicate killifish to thrive and display natural surface behaviours.

Breeding

Typically spawns in fine plants or spawning mops. Condition a pair with high-quality live foods, then provide spawning media such as Java moss or yarn mops. Eggs are often laid singly and may be removed for separate incubation. Fry are tiny and should be started on infusoria or other very small live foods, graduating to newly hatched brine shrimp after a few days. Breeding success is highest in soft, slightly acidic water with gentle filtration and abundant fine-leaved plants. Remove adults to prevent egg predation.

Why Buy from Tropical Fish Co

Tropical Fish Co is a trusted UK supplier of rare and specialist tropical fish, including hard-to-find killifish species like Rivulus cylindraceus. We guarantee healthy, well-conditioned stock, expert care advice, and secure nationwide delivery. Every fish is quarantined and inspected before dispatch, ensuring you receive only the finest specimens. Whether you're setting up a dedicated killifish tank or adding a rare species to your collection, Tropical Fish Co offers unmatched quality and customer service. Order online today and bring the beauty of Cuban waters into your home aquarium.