Green/Brown Rivulus (Rivulus cylindraceus)

Overview

The Green/Brown Rivulus (Rivulus cylindraceus) is a small Cuban killifish with far more colour than the old plain-brown reputation suggests. FishBase lists the common name as Green Rivulus, while the supplier name also includes Brown Rivulus; both names are useful because settled males can show olive, bronze, orange and blue-green tones depending on light, diet and mood. This SKU is supplied at about 3-4 cm, and FishBase records adults up to about 5.5 cm total length.

This is not a seasonal annual killifish. FishBase specifically notes that it is not seasonal and is easy to maintain in aquaria, so the care should not be copied from peat-incubating annual species. Think of it instead as a quiet, covered, planted-aquarium rivulus: a small surface-to-midwater fish that likes cover, clean stable water and small meaty foods. It is peaceful, but it is still a specialist fish that shows best in a calm species-first setup or with very careful tank mates.

Quick Facts

• Scientific name: Rivulus cylindraceus
• Common names: Green Rivulus, Brown Rivulus, Cuban Rivulus
• Supplied size: about 3-4 cm
• Adult size: up to about 5.5 cm total length
• Origin: coastal river basins of Cuba
• Best setup: covered, planted, low-flow aquarium
• Routine temperature: 22-24 C, with stable conditions more important than chasing extremes
• Diet: small live/frozen foods plus quality tiny prepared foods if accepted
• Breeding type: non-annual plant or mop spawner with adhesive eggs

Appearance

The body is compact and cylindrical, with a warm orange-bronze upper line, a cooler blue-lilac sheen along the flank, yellow edging in the fins and a dark tail area with pale spotting. Under subdued light and floating plants, males can look far richer than the name Brown Rivulus suggests. Females are usually plainer, often with a neat caudal spot, but they still have the same alert, hovering rivulus posture.

Colour improves when the fish feels secure. Use dark planting, floating cover, leaf litter if you like a natural look, and gentle lighting rather than a bright bare tank. The fish often pauses almost motionless under cover, then darts for food. That stop-start behaviour is normal and is part of the appeal.

Natural Habitat

FishBase places Rivulus cylindraceus in the coastal river basins of Cuba, with records from upland streams and clear vegetated rivers and lakes. The American Killifish Association also describes it as a Cuban freshwater-stream fish that uses fresher streams feeding bays and rivers rather than the saltier habitats preferred by mangrove rivulus. Older British Killifish Association notes describe small flowing streams and emphasise how quickly the fish can leap from the water.

In the aquarium, that habitat translates into clean water, plenty of cover, gentle movement and a secure lid. A tight cover is not optional. Rivulus can jump through very small gaps, especially during feeding, display or sudden disturbance.

Aquarium Care

A pair can be managed in a small specialist tank, but for a polished long-term display we recommend at least 40 litres for a pair or small group. A larger planted aquarium gives more stable water, better cover and fewer squabbles. Use a sponge filter or gentle outlet, avoid strong current, and keep the surface broken up with floating plants such as Salvinia, Amazon frogbit or floating stems. Java moss, fine-leaved plants and root tangles help the fish feel safe and also give spawning sites.

Use a routine temperature around 22-24 C. Aim for near-neutral water, around pH 6.8-7.5, and moderate softness, around 5-10 dGH. Do not chase numbers aggressively if your water is clean and stable. Small regular water changes are better than sudden corrections.

Feeding

This is a small carnivorous killifish. Offer tiny live and frozen foods such as daphnia, brine shrimp, mosquito larvae, whiteworm, grindal worm and finely chopped bloodworm. Good micro-pellets can be used once the fish accepts them, but live and frozen foods keep condition, colour and breeding behaviour much better. Feed small portions and remove leftovers quickly, especially in planted nano-style setups where water can foul fast.

Temperament and Tank Mates

Green/Brown Rivulus are peaceful, but they are not built for a busy community aquarium. Fast feeders, fin-nippers and large fish will either outcompete or stress them. The safest route is a species-first tank. If you do add companions, choose only very calm fish that stay small and do not dominate the surface. Gentle killifish or small planted-tank species may work, but tiny fry and very small shrimp can be eaten.

For similar quiet killifish options, compare our Berkenkamp's Epiplatys, Graham's Epiplatys and Togo Panchax. Those pages are useful when deciding whether you want a surface-oriented African killifish or this Cuban rivulus.

Breeding Notes

Breeding is realistic for patient keepers. British Killifish Association notes describe spawning in floating plants or nylon mops, with large adhesive eggs and hatching in about ten to fourteen days. Set up a quiet pair, condition them with live foods, then check the mop or fine plants regularly. Eggs can be collected and incubated separately, or left in a mature planted tank if you are not trying to save every fry. Fry are small and need suitable first foods, then newly hatched brine shrimp as they grow.

Why Buy This Fish From Tropical Fish Co?

For this SKU, the exact Petra source photo is included alongside the existing aquarium-context gallery, so you can inspect the fish rather than relying on generic artwork. New customers can use the WELCOME10 first-order discount when eligible, and our Live Arrival Guarantee applies under the published delivery terms.

Choose Green/Brown Rivulus if you want a small Cuban killifish with subtle colour, interesting surface behaviour and manageable care. Give it a lid, plants, gentle water movement and a varied small-food diet, and it becomes a rewarding specialist fish rather than a throwaway nano tank add-on.