Golden wonder killifish

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 feeder with a predatory streak. Flake, floating pellets, frozen bloodworm, frozen brine shrimp, live food (fruit flies, mosquito larvae, small crickets, live guppies for larger specimens). They hunt by lurking at the surface and ambushing anything that falls in or swims past. Live food triggers the most active feeding behavior. In community tanks, they eat floating food before it can sink to other fish. Feed once or twice daily.

Compatibility

• Surface-dwelling predator. Despite being a killifish, golden wonders are large enough (7–8 cm) to eat small fish. Anything that fits in their upturned mouth is food: neon tetras, guppies, small rasboras, and shrimp.
• Best with medium-sized tankmates that stay in the lower water zones: corydoras, medium tetras (black skirt, serpae), barbs, and loaches. The golden wonder patrols the surface and ignores fish below it that are too large to swallow.
• Males are territorial toward other males at the surface. One male per tank in smaller setups (under 100 L). In larger tanks, multiple males coexist if surface area is sufficient.
• Hardy, undemanding, and visually striking. The gold body with iridescent blue scales under certain lighting makes them an appealing surface fish for medium-sized community tanks.

Origin and habitat

The golden wonder is a bright yellow-gold aquarium form of the striped panchax, Aplocheilus lineatus, a killifish native to fresh and slightly brackish waters of Peninsular India and Sri Lanka. Valenciennes described it in 1846. In the wild it lives in streams, rivers, swamps, reservoirs, and rice paddies, and it has been moved into various waters as a mosquito-control fish because it readily takes insect larvae at the surface. Wild fish are olive-brown above with rows of metallic green-gold and red flank spots; the golden wonder is the selectively bred colour form. Most males reach about 7 cm, though the fish can grow to around 10 cm in good conditions late in life. The body is built for surface hunting: slender, with the dorsal fin set well back, a long anal fin, and an upturned mouth. On top of the head it carries a parietal eye, a light-sensitive spot that helps it watch the surface above for insects and threats. It is a strong jumper, so a tight-fitting lid is essential.

Breeding

An egg-laying species that places its eggs among floating plants at the surface over an extended spawning period rather than all at once. A pair keeps producing eggs day after day, and in the wild the species is a prolific breeder. The eggs are large and can be picked off floating roots, java moss, or a spawning mop by hand, which is the simplest way to save them from the adults, who eat both eggs and fry. Incubation takes roughly two weeks, and the fry are large enough to take baby brine shrimp from the start. Growth is quick, and a well-planted species tank with surface cover produces a steady supply of young.

Common problems

The main surprise for new keepers is predation. The upturned mouth and surface-ambush habit mean small tankmates such as neon tetras, endlers, and small rasboras gradually vanish, so tankmates need to be big enough not to fit in the mouth. Jumping is the other real risk; the fish leap to grab insects and slip through any gap in the cover, so a tight lid is not optional. Beyond that the species is hardy across a broad range of conditions and tolerates a little salinity, and disease is uncommon apart from the occasional ich outbreak in stressed new arrivals.

Bioload

Further reading

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