Acanthopsis choirorhynchos

The Horseface Loach is a unique freshwater fish from Southeast Asia known for its long snout and habit of burying itself completely in the sand substrate. This distinctively shaped bottom-dweller is often sought after for its amusing behavior and ability to keep the aquarium substrate clean. As their name suggests, they possess a long, horse-like head which they use to dig for food and hide from potential predators. They are generally peaceful creatures that prefer to live in groups, making them excellent candidates for community tanks that house other non-aggressive species.

To ensure these fish thrive, the most critical requirement is a soft, fine sandy bottom. Because they spend a significant amount of time burrowed beneath the surface with only their eyes protruding, sharp gravel or coarse substrates can damage their delicate skin and sensory barbels. They are active scavengers that will happily eat sinking foods, helping to clear up uneaten remnants from other fish. While they are usually calm, they can be surprisingly fast swimmers when startled. Owners should ensure the tank has a secure lid, as these loaches may attempt to jump out if they feel threatened or if water conditions are not ideal.

The Horseface Loach presents a fascinating subject for aquarists interested in bottom-dwelling species from Southeast Asian river systems. Physically, this fish is characterized by its elongated, taeniform body and a dramatically extended snout, which houses highly sensitive barbels. These sensory organs are crucial for their survival, allowing them to detect invertebrates and organic matter buried deep within the riverbed. In the home aquarium, mimicking their natural environment is essential for their long-term health. The most vital component of their care involves the substrate; it must be composed of deep, soft sand. This species exhibits a specific behavior where they take in mouthfuls of sand, sift out edible organic matter, and expel the clean sand through their gill openings. This constant sifting action oxygenates the substrate and prevents the buildup of anaerobic pockets.

In terms of water conditions, these loaches require well-oxygenated, clean water with a moderate current to simulate the flowing rivers of their origin. They are sensitive to the accumulation of organic waste, so robust filtration and regular maintenance are necessary to keep dissolved solids and nitrates low. While they are generally peaceful towards tank mates, their size and activity level require a spacious environment. They are social animals that exhibit shoaling behavior; keeping a solitary individual can lead to stress and shyness. When kept in groups, they are more confident and more likely to be seen foraging during the day, although they retain strong nocturnal tendencies.

Feeding the Horseface Loach requires ensuring food actually reaches the bottom of the tank. They are omnivorous scavengers that feed on benthic organisms in the wild. In an aquarium, they accept a variety of high-quality sinking pellets, wafers, and live or frozen foods like bloodworms and brine shrimp. However, because they are often outcompeted by aggressive mid-water feeders, care must be taken to target feed them after lights out if necessary. Aquarists should also be aware of their interaction with live plants. While they do not eat plant matter, their burrowing habits can uproot delicate vegetation that is not firmly established. Therefore, using potted plants or species that attach to driftwood and rocks is often a more practical approach for a tank designed around this species.

The species Acanthopsis choirorhynchos, commonly known as the Horseface Loach, belongs to the family Cobitidae. It is a benthic freshwater fish endemic to the swift-flowing river basins of Southeast Asia. Taxonomically, the genus Acanthopsis has undergone various revisions, and this specific species is often confused with morphologically similar congeners such as Acanthopsis dialuzona. Accurate identification often requires close examination of the snout length, caudal patterns, and specific biometric data, as the 'Horseface' common name is frequently applied to multiple members of the genus indiscriminately.

Morphologically, the species differs from many other loaches due to its extreme head elongation. The snout is long and tubular, terminating in a small, inferior mouth surrounded by multiple pairs of barbels. These barbels are tactile and chemosensory organs adapted for foraging within soft substrates. A defining characteristic of the Cobitidae family present in this species is the suborbital spine. This erectile, bifid spine is located below the eye and acts as a defense mechanism; when the fish is threatened or handled, the spine is extended, which can become entangled in nets or inflict injury on predators. The body is encased in small, cycloid scales and is streamlined to reduce drag in currents, aiding its ability to make rapid bursts of speed.

Ecologically, Acanthopsis choirorhynchos functions as a macroinvertebrate predator and scavenger. By burrowing into the riverbed, they play a minor but present role in bioturbation, mixing sediment layers and influencing the benthic micro-environment. Their physiological adaptation allows them to remain buried for extended periods, likely relying on a combination of low metabolic phases and water exchange over the gills through the sand matrix. Conservation assessments list them as Least Concern, yet they face localized threats from habitat alteration and pollution in their native drainage basins.

Breeding the Horseface Loach in captivity is an extremely difficult endeavor and reports of successful, intentional spawning in home aquaria are virtually non-existent. Currently, the vast majority of specimens available in the ornamental fish trade are wild-caught from their native habitats in Southeast Asia. Consequently, there is no established protocol for breeding commercial numbers of this species, and data regarding their specific reproductive triggers in a closed system is scarce.

Sexual dimorphism in this species is not strongly marked, making the identification of pairs challenging for hobbyists. There are no obvious differences in color or finnage between males and females. The only reliable indicator of sex is often observed only in fully mature, well-conditioned adults, where the female may appear noticeably rounder or fuller in the abdominal region due to the development of roe. Males are generally more slender, though this distinction can be subtle and difficult to confirm without a side-by-side comparison of multiple individuals.

Based on their family classification, they are presumed to be egg scatters that do not practice parental care. In the wild, spawning is likely triggered by seasonal changes associated with the monsoon cycles, which bring about fluctuations in water temperature, pH, hardness, and flow rate. These environmental cues are difficult to replicate precisely in an aquarium. It is hypothesized that they would require a significant drop in temperature followed by a massive influx of fresh, soft water to simulate the rainy season, alongside an increase in live food availability. Because successful captive breeding has not been documented, there are no specific instructions for raising fry, though it is assumed they would require microscopic infusoria immediately after absorbing their yolk sacs, similar to other Cobitidae larvae.