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 form is an aquarium-bred color morph of the striped panchax (Aplocheilus lineatus), native to Peninsular India and Sri Lanka. Described by Valenciennes in 1846. Found in streams, reservoirs, rivers, swamps, paddy fields, and even slightly brackish water. In India, introduced to various areas for mosquito control. Wild fish are olive-brown on the back with pale flanks carrying rows of metallic greenish-gold and red spots, sometimes linked into stripes. The golden wonder is a selectively bred variant with brighter yellow-gold coloring. Size around 7 cm, growing up to 10 cm under excellent conditions. Lifespan around six years. Non-annual; unlike many killifish, this species lives several years. The anatomy is built for surface predation: a slender body with a short-based dorsal fin set far back, a long anal fin, and an upward-facing mouth. Possesses a parietal eye, a light-sensitive organ on top of the head (visible as an iridescent white spot between the eyes) that detects prey insects and predators above. Accomplished jumpers. A tight-fitting lid is mandatory. Predatory toward smaller fish like tetras and rasboras.

Breeding

Egg depositor that attaches eggs to floating plants over a period of days. A pair produces 5-15 eggs daily among floating plant roots, java moss, or spawning mops at the surface. Eggs are relatively large and can be picked off by hand. Adults eat eggs and fry, so either collect eggs daily or provide very dense floating cover. Eggs hatch in 12-14 days at 25°C. Fry are comparatively large and can eat baby brine shrimp from day one. Growth is fast; fry reach 2–3 cm within a month. The species breeds readily in home aquariums without special conditioning. A well-planted surface in a species tank produces a steady stream of fry.

Common problems

Predation on small tankmates is the main issue new keepers encounter. The upturned mouth and surface-hunting behavior mean that neon tetras, endlers, and small rasboras disappear from the tank over time. Match with appropriately sized tankmates. Jumping is a significant risk; golden wonders launch from the water to catch insects and will exit through any gap in the lid. A tight cover is mandatory. Health problems are uncommon; the species is hardy across a wide range of conditions (pH 6.0-8.0, temperature 22–28°C, tolerates some salinity). Ich is rare except in stressed new arrivals.

Bioload

Further reading

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