Arnold's Killie (Fundulopanchax arnoldi)

Species Overview

Arnold's Killie is a colourful West African killifish best listed under the accepted name Fundulopanchax arnoldi. The older aquarium and supplier name Aphyosemion arnoldi is kept here as synonym context.

This listing is for young fish supplied at approximately 3-4 cm. They should not be planned as a permanent 3.5 cm nano fish: FishBase lists males up to 7.4 cm total length, while the British Killifish Association describes good aquarium males around 2.25 inches. Give them the calm cover and adult space a specialist killifish deserves.

Name, Range and Habitat

FishBase records Fundulopanchax arnoldi from southern Nigeria, and specialist killifish sources place it mainly in the Niger Delta area. The British Killifish Association notes slow-moving streams and brooks near Warri, with other populations reported from Oweri. AKA reference material also points to Niger Delta and nearby coastal rainforest waters.

The habitat is important for care. FishBase describes temporary swamps and swampy parts of smaller brooks in coastal rainforest. These are sheltered, plant-filled, low-flow waters, not bright open aquariums with hard water and strong current. In the aquarium, the closest practical match is a covered, mature, softly lit planted setup with roots, moss, floating cover and gentle filtration.

Appearance and Display Value

Mature males can be spectacular when settled. BKA descriptions include light orange to brown base colour, pale green along the back, a shining green eye, red-edged lips, crimson markings on the head and flanks, and large rounded fins with blue-green, orange and crimson patterning. Mature males may also show streamers on the tail lobes.

Females are much plainer, usually olive-green to drab with partial dark bars or small flank spots and transparent fins. That difference is normal and useful. A mixed pair or trio gives better natural behaviour than keeping a single fish as a decoration.

Aquarium Setup

A pair or trio can be kept in a mature species aquarium from around 40 litres, provided water quality is stable and the layout gives shade and cover. For a small group or a mixed peaceful display, use more space and more broken sight lines so males can display without constantly pressuring females.

A tight lid is essential. Killifish are jumpers, especially during settling, feeding or sudden disturbance. Use floating plants, moss, spawning mops, Java fern, Anubias, roots and leaf litter to create security. A dark substrate and diffused light help the fish colour up and feel less exposed.

Filtration should be gentle but reliable. Sponge filters or softened outlets are ideal. Avoid harsh current, bare tanks, bright lighting without cover and recently set up aquariums with unstable water chemistry.

Water Parameters

The supplier range for this stock is 22-25 C, pH 5.8-7.2 and 5-15 dGH. FishBase gives the same temperature and pH range, while the BKA notes that the species can be fussy about water and may not tolerate hard water for long. BKA maintenance guidance points toward about pH 6.4 and 2-4 degrees German hardness.

For everyday care, aim for clean, stable, soft to moderately soft water. Avoid keeping them warm for no reason; specialist notes warn that prolonged high temperatures can shorten lifespan. If your tap water is very hard, blend gradually with remineralised RO water rather than making sudden chemistry changes.

Feeding

Arnold's Killie is a small carnivorous predator. Offer live or frozen daphnia, cyclops, mosquito larvae, brine shrimp, grindal worm and small bloodworm. Some fish accept quality micro pellets or soft granules, but live and frozen foods are the best route to colour, condition and breeding readiness.

Feed small portions once or twice daily. In compact planted tanks, remove uneaten food quickly so the soft-water setup stays clean. If new arrivals are shy, begin with small moving foods and dim light; confident feeding is one of the best signs that they have settled.

Temperament and Tank Mates

This is a peaceful killifish, but it is not a fish for loud, fast tank mates. The safest display is a species-focused aquarium with one male and two females, or a carefully managed small group with enough cover for weaker fish to avoid attention.

If tank mates are used, choose only very calm small fish that share soft, quiet water and will not rush food. Avoid fin nippers, large cichlids, predatory fish, boisterous tetras, hard-water specialists and uncovered aquariums. Shrimp fry may be eaten, and larger shrimp can disturb tiny eggs or fry.

Breeding Notes

FishBase records the species as a bottom spawner with about two months incubation. Killi.co.uk says it is typically spawned over peat in aquariums, and AKA notes describe peat as a good egg-laying substrate with semi-dry incubation commonly around 6-10 weeks.

A separate breeding setup is recommended. Use soft clean water, floating cover, peat fibre, coconut fibre or a suitable spawning medium, and condition adults with live and frozen foods. Fry are small, so very fine first foods may be needed before newly hatched brine shrimp is accepted.

Common Mistakes to Avoid

Do not treat Arnold's Killie as a throwaway tiny community fish. The important corrections are simple: cover the tank, keep the water soft and stable, provide shade, and feed small meaty foods.

Do not keep it in hard alkaline water for long periods, do not run it too warm without need, and do not place a single specimen into a busy display where faster fish steal all food. A quiet, mature, planted aquarium is where the species becomes worth keeping.

Who This Fish Suits

Choose Arnold's Killie if you like detailed behaviour, specialist aquariums and rare West African killifish. It is a good fit for keepers who enjoy planted tanks, natural cover, small foods and careful water changes.

It is less suitable for a first hard-water community aquarium or a high-flow display. The care is not difficult in the right setup, but the fish asks for a more deliberate style of fishkeeping than the old generic copy suggested.

Photo and Size Notes

The source photo added to this listing shows the real supplier type alongside the existing aquarium visuals. Colour on arrival may vary with sex, maturity, stress, lighting and diet. Young 3-4 cm fish may need time to settle before showing adult male patterning.

Plan the adult aquarium before ordering. It is kinder to provide the lid, cover and soft-water routine from day one than to correct problems after the fish has started hiding, jumping or losing food to faster tank mates.

Arrival and Live Arrival Guarantee

Acclimate Arnold's Killie slowly into a mature aquarium with matching temperature and low light. Float the sealed bag to equalise temperature, then add small amounts of tank water gradually over 30-45 minutes. Keep the first evening quiet and feed lightly once the fish is alert.

Tropical Fish Co ships live fish with care, oxygen, insulation and weather-aware packing. Eligible livestock orders are supported by our Live Arrival Guarantee, provided the delivery and acclimation guidance is followed and any issue is reported promptly with clear photos.

Source Notes

Care notes were checked against FishBase for taxonomy, range, water, adult-size and breeding data; the British Killifish Association for Niger Delta habitat, colour, maintenance and hard-water caution; Killi.co.uk and AKA reference material for distribution and peat-spawning context.