Blue panchax

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Feeding

Surface-feeding micropredator. Accepts dry foods (small pellets, flake) but coloration and breeding condition are visibly better with regular live or frozen meaty food: bloodworm, mosquito larvae, daphnia, and brine shrimp. The natural diet leans heavily on insects and insect larvae taken from the surface film, which is why the species has been used as a biological mosquito-control agent in several countries. The upturned mouth means food sinking past the surface gets ignored quickly, so feed in small amounts that get eaten before they drop. Twice a day is plenty.

Compatibility

• Surface-dwelling micropredator with a wider mouth than first appearance suggests. Will eat neon tetras, ember tetras, micro-rasboras, cherry shrimp, and small fry. Match with mid-sized peaceful species that occupy other zones
• A strong jumper; a tight cover with no gaps is essential. Glass canopies or properly-trimmed plastic hoods, not loose lids
• Males can be territorial in confined spaces; one male per tank with several females, or a larger group of four-plus males in a longer tank with broken sightlines
• Tolerates brackish water and is found across a wide salinity range in the wild; thrives in fresh water but adapts to slightly brackish setups as well
• Often confused with green panchax (A. blockii), dwarf panchax (A. parvus), and Werner's killifish (A. werneri); the distinguishing field-mark on this species is the bright silvery-white spot on top of the head

Origin and habitat

A small surface-dwelling killifish from South and Southeast Asia, native from Pakistan east through Nepal, India, Bangladesh, Sri Lanka, Myanmar, Cambodia, and Vietnam into the Indo-Malayan archipelago (peninsular Malaysia, the major Sunda islands, and Timor-Leste); also recorded from the Seychelles, discovered in two hot springs in Singapore, and commonly found in rivers and estuaries around Johor Bahru. Wild habitat is broad: lowland ponds, ditches, canals, reservoirs, rice paddies, mangrove creeks, and estuaries. The species tolerates fresh, brackish, and even hypersaline conditions, and records note it prefers clear water with dense rooted or floating macrophytes. Hamilton described the species in 1822 in 'An account of the fishes found in the river Ganges and its branches' under the name Esox panchax, placing it in the pike genus; it later went through Haplochilus (Day 1878), Panchax (Weber & de Beaufort 1922), and was settled in Aplocheilus by Smith in 1945. The genus name combines Greek aploe 'simplicity' with cheilos 'lip'. It has been widely introduced beyond its native range as a mosquito-control fish, sometimes with knock-on harm to local biodiversity. The body is elongated and torpedo-shaped with an upward-pointing mouth, and the diagnostic feature is the bright silvery-white spot on top of the head that gives the species its alternative trade name 'whitespot'. Colour varies considerably across the wide range: pale yellow to greenish ground with a blue iridescent sheen under good light, scales with darker margins forming a net pattern over the back, a dorsal fin with a black basal spot, and dark-rimmed caudal and anal fins in well-conditioned males. Beck and colleagues (2017) sequenced two mitochondrial and three nuclear markers across the range and recovered three major mitochondrial clades within A. panchax, with patterns consistent with isolation in palaeodrainage basins during Pleistocene glacial cycles and sea-level fluctuations. Adults reach a maximum of 9 cm total length, with around 5 cm being typical and sexual maturity at roughly 4 to 5 months. IUCN Least Concern.

Breeding

Among the easier killifish to breed at home. Unlike annual killifish species, the eggs are not diapausing and do not need a dry period. Condition a pair (or one male with two or three females) on live or frozen food, then move the group into a softwater breeding tank with floating and fine-leaved plants near the surface. Temperature around 25 C tends to trigger spawning. The female deposits relatively large eggs onto vegetation near the surface, scattering them over several days; the egg shell is robust enough to be picked off and transferred to a separate rearing container if the keeper wants to maximise survival, otherwise the parents and other tankmates will eat them. The species is oviparous with no parental care. Hatching takes around 9 to 14 days depending on temperature. Fry are large enough to take baby brine shrimp from day one, and growth is steady on standard fry foods. In the wild the species is a perennial breeder, with a peak through the rainy season from November to March.

Common problems

Jumping is the leading cause of death. The fish lives at the very top of the water column and is a capable leaper; a tight-fitting lid with no openings around heater wires or filter outlets is essential. Predation on tankmates is the second issue: the mouth is surprisingly wide and the fish will eat anything small enough to swallow, which means cherry shrimp, micro-rasboras, neon-tetra-sized fish, and small fry are all at risk despite the species's mild general temperament. Match it with fish too large to fit in the mouth. Male-on-male aggression appears in cramped tanks; either keep one male per tank with two or three females, or use a longer tank with visual barriers. Note that records list the species as 'difficult to maintain in aquarium' while most current aquarist sources call it hardy and beginner-friendly; the discrepancy probably reflects older literature when wild-caught stock dominated the trade. Modern captive-bred fish are easy. Colour fades under bright top lighting with a pale substrate; a darker tank shows the iridescence at its best.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size