Aplocheilus lineatus

The Striped Panchax, often sold as the Golden Wonder Killifish, is a vibrant and active fish that brings a lot of life to the top level of an aquarium. With its shimmering golden-yellow body and streamlined shape, it’s a beautiful addition for keepers with some prior experience. This fish is a surface-dweller, meaning it will spend almost all its time near the top of the water, looking for food. Speaking of food, it is a carnivore and needs a high-protein diet. While it enjoys flakes and pellets that float, it truly thrives when given treats like frozen or live foods.

Originating from the slow-moving waters of Asia, it feels most at home in an aquarium with low water flow. A very strong current from a filter can stress it out. A secure lid on the tank is absolutely essential, as this fish is a natural jumper and can easily escape an open-topped aquarium. While they are fascinating to watch, their territorial nature and predatory instincts mean they are not suitable for a community tank with very small fish, like Neon Tetras or any shrimp, as these will likely be seen as a meal. They do best with larger, peaceful fish that occupy the middle and bottom of the tank. To feel secure and display their best behavior, they should be kept in a small group of at least four. This helps to spread out any aggression and encourages more natural social interactions.

Aplocheilus lineatus, commonly known as the Striped Panchax or its popular color morph, the Golden Wonder Killifish, is a captivating top-dwelling species that offers a dynamic presence in a well-planned aquarium. While its care is rated as moderately difficult, this is primarily due to its specific social and environmental needs rather than a delicate constitution. In fact, its tolerance for a wide range of pH and water hardness makes it quite adaptable, provided the environment remains stable and free of sudden fluctuations.

For a successful habitat, an aquarium of at least 60 liters is required, but a larger tank (90-120 liters) is highly recommended to accommodate a proper school and dilute territorial disputes among males. Aquascaping should aim to replicate its natural environment: heavily vegetated, slow-moving waters in Asia. This is best achieved using a gentle filter output, such as a spray bar aimed at the glass, to minimize surface agitation. Floating plants like Frogbit (Limnobium laevigatum), Red Root Floaters (Phyllanthus fluitans), or even dense surface mats of Hornwort are highly beneficial. They provide essential cover, reduce stress by diffusing light, and offer a natural spawning medium. A tight-fitting lid is non-negotiable. As energetic jumpers and surface-breathers, they will investigate any gap and can easily leave the water, especially when startled.

Socially, the Striped Panchax is complex. A minimum school size of four is necessary, but a larger group of 6-8 in a spacious tank is ideal for observing more natural shoaling behavior. It's crucial to maintain a proper gender ratio, typically one male to two or three females. This prevents the dominant male from focusing his territorial aggression and breeding pursuits on a single female. Tank mates must be chosen with extreme care. Their predatory instinct is a defining trait; any fish or invertebrate that can fit in their surprisingly large mouth will eventually become a meal. This rules out nano fish like Celestial Pearl Danios, small tetras, all shrimp species, and fish fry. Good companions include larger, robust mid-water species like Congo Tetras and Black Skirt Tetras, as well as bottom-dwellers like Corydoras catfish and various Loricariidae.

As active carnivores with a medium metabolism, their diet must be varied and protein-rich. A high-quality floating flake or pellet can form the staple, but it must be supplemented several times a week with frozen or live foods. Bloodworms, daphnia, brine shrimp, and mosquito larvae are all excellent choices that will trigger their natural hunting response and ensure they receive a full range of nutrients for optimal health and vibrant coloration.

Breeding is a straightforward affair for the prepared hobbyist. These are continuous egg-scatterers, depositing adhesive eggs daily amongst the roots of floating plants or on a purpose-made yarn spawning mop. There is no parental care, and adults will predate their own eggs and fry relentlessly. For successful rearing, it's best to move the egg-laden plants or mop to a separate, mature rearing tank with sponge filtration and a similar water chemistry.

Aplocheilus lineatus is a species of freshwater ray-finned fish classified within the family Aplocheilidae, a group of Old World killifish in the order Cyprinodontiformes. Native to lentic and lotic environments across the Indian subcontinent and Sri Lanka, including streams, rivers, ponds, and man-made systems like paddy fields. Its current IUCN conservation status of "Least Concern" (LC) is indicative of its broad geographic distribution and environmental resilience.

The morphology of A. lineatus is highly adapted for its ecological niche as a surface-dwelling predator. It possesses an elongated, fusiform body that is sub-cylindrical anteriorly and becomes more laterally compressed towards the caudal peduncle. A key diagnostic feature is its superior mouth, which is prognathous and upturned, an efficient tool for capturing prey—primarily allochthonous insects and aquatic larvae—from the air-water interface. This is complemented by its ability as a facultative air-breather. This physiological mechanism allows it to supplement gill respiration with atmospheric oxygen, a critical adaptation for surviving in the often hypoxic, heavily vegetated, or stagnant waters that constitute its natural habitat.

The species exhibits considerable physiological plasticity, tolerating a wide euryhaline-like range of freshwater chemical parameters, including a pH from 6.0 to 8.0 and hardness from 36 to 215 ppm. It also tolerates minimal salinity (up to 2 ppt), suggesting a capacity to inhabit upper estuary zones. In an aquarium setting, its biological load is considered moderate, with a calculated bioload factor of 3.0 reflecting its carnivorous diet, medium metabolic rate, and subsequent nitrogenous waste output. Thus, efficient biological filtration is a prerequisite for its long-term husbandry.

Ethologically, A. lineatus is an active, fast-swimming species. While it naturally forms loose shoals, it also displays marked intraspecific territoriality, particularly among males competing for surface space and breeding opportunities. Its predatory behavior is a classic example of gape-limited predation, where any organism of a suitable size is identified as potential prey.

Reproductive biology is characterized by a fractional spawning or egg-scattering strategy without parental investment. Females deposit adhesive eggs onto fine-leaved or floating vegetation over an extended period. This reproductive mode, coupled with its adaptability and four-year captive lifespan, has contributed to its successful establishment in the aquarium hobby and its resilience in natural ecosystems.