Thoracocharax stella

The Spotfin Hatchetfish is a captivating South American species highly prized for its unusual body shape and strictly surface-oriented behavior. In its native habitat of slow-moving rivers and tributaries, it lives at the water's surface, preying on insects and other small invertebrates. Replicating this environment is key to its successful care. A sizeable aquarium with low water flow is recommended to accommodate a shoal, as these are active swimmers that require ample space. Most importantly, the tank must be equipped with a tight-fitting lid, as these fish are notorious escape artists, capable of launching themselves completely out of the water with surprising force. Floating plants are highly beneficial, as they provide cover, diffuse lighting, and create a more natural and secure environment for these sometimes-timid fish.

As a dedicated shoaling species, the Spotfin Hatchetfish must never be kept singly. A group of at least six individuals is the minimum requirement to ensure their well-being, reduce stress, and encourage their fascinating social interactions. In a group, they will be more confident and active. They are generally peaceful towards other species and can be housed in a community setting with tank mates that are not large enough to eat them and that do not occupy the top water stratum. Good companions include tetras, corydoras, and dwarf cichlids. A carnivorous diet is essential. They should be fed daily with high-quality floating foods. While they may accept flakes and freeze-dried options, their diet should be supplemented with frozen and live foods to ensure optimal health. Due to its medium metabolism, it produces a relatively low amount of waste, but maintaining pristine water quality through regular maintenance is still crucial for this moderately sensitive species.

Thoracocharax stella, commonly known as the Spotfin Hatchetfish, is a freshwater characin belonging to the family Gasteropelecidae. This family is distinguished by its members' extreme morphological adaptations for a surface-dwelling lifestyle. The most prominent feature of T. stella is its deeply compressiform body shape, characterized by an exceptionally developed and enlarged sternal region that forms a deep, disc-like keel. This structure houses the powerful pectoral muscles responsible for the fish’s ability to make powerful leaps from the water, a behavior used for evading predators and potentially capturing terrestrial insects. Its classification as a validated species within the Thoracocharax genus solidifies its taxonomic standing.

Ecologically, T. stella occupies the top stratum of the water column in its native South American river systems. It thrives in low-flow environments, often with acidic water chemistry resulting from decaying organic matter. Its diet is primarily carnivorous, specializing in surface-dwelling and terrestrial invertebrates that fall onto the water. This feeding strategy classifies it as a surface insectivore. Physiologically, it has a medium metabolic rate and corresponding oxygen consumption, consistent with its active but not hyperactive swimming behavior. Despite its activity, it has a relatively low bioload factor, producing minimal waste compared to other fish of similar size. From a conservation standpoint, T. stella is currently listed as 'Least Concern' (LC) by the IUCN, indicating that it has a widespread distribution and is not facing immediate threats in its natural habitat, making it a sustainable choice for the aquarium trade.

Breeding the Spotfin Hatchetfish in a home aquarium is considered difficult and represents a significant achievement for the dedicated hobbyist. Success requires a carefully prepared, dedicated breeding tank. This tank should contain warm, very soft, and acidic water to simulate the rainy season conditions that trigger spawning in the wild. Gentle filtration, such as an air-driven sponge filter, is essential to protect the delicate eggs and fry from being damaged or drawn in. The lighting should be dim, and the inclusion of dense floating plants is critical, as they provide the preferred medium for egg deposition and give the adult fish a sense of security.

Sexing these fish is notoriously challenging, as there are no obvious external differences between males and females. The most reliable, albeit subtle, indicator is that a female full of eggs (gravid) may appear slightly fuller and more rounded in her abdominal region when observed from above. To maximize the chances of having a compatible pair, it is best to start with a healthy, well-conditioned group of six or more individuals. Conditioning involves feeding the group a protein-rich diet of live and frozen foods for several weeks to encourage reproductive readiness. During spawning, the female will scatter her adhesive eggs amongst the roots and leaves of floating plants. The parents exhibit no parental care and will predate on their own eggs. Therefore, it is imperative to remove the adult fish as soon as spawning is complete. The eggs typically hatch within one to two days. The newly hatched fry are minuscule and will require microscopic foods like infusoria or liquid fry food. As they grow, they can be transitioned to larger foods such as microworms and newly hatched brine shrimp. Meticulous attention to water quality is paramount during this fragile stage of development.