Ariopsis seemanni

The Colombian Shark Catfish, also known as the Tete Sea Catfish or Silver Tipped Shark, gets its name from its shark-like body shape and active swimming style, but it is a true catfish, not a shark. A common mistake made with this fish is keeping it in freshwater. While often sold as a freshwater species, it is a brackish water fish, meaning it requires salt in its water to stay healthy and thrive. Without salt, its health will decline over time.

These are social and energetic fish that should be kept in small groups. Because they need friends and grow to be quite large—well over a foot long—they require a very large aquarium. A small tank is not suitable for even a single individual, and a group needs plenty of room to swim. They are not picky eaters and will eagerly accept a variety of sinking fish foods, but their hardy appetite means they produce a lot of waste, making powerful filtration a must.

Due to their specific need for salty (brackish) water, their large adult size, and their requirement for a spacious tank with excellent filtration, they are considered a challenging species to care for. They are best suited for experienced fishkeepers who are prepared to provide a large, specialized brackish water environment.

The Colombian Shark Catfish (Ariopsis seemanni) is a dynamic and impressive fish that presents a rewarding challenge for the dedicated aquarist. Its most critical care requirement is the provision of a brackish water environment. Juveniles are often found in low-salinity estuaries, but as they mature, they migrate to more saline waters. In the aquarium, this means starting juveniles at a low specific gravity (around 1.002-1.005) and gradually increasing the salinity as they grow, reaching up to 1.020 for fully grown adults. This euryhaline nature is central to their long-term health.

An appropriately sized aquarium is non-negotiable. Given their potential to exceed 30 cm and their shoaling nature, a tank with a large footprint is essential to provide adequate horizontal swimming space for a group. They are active swimmers that utilize both the bottom and middle water columns. Consequently, the aquarium decor should consist of a sandy substrate to protect their sensitive barbels, with ample open space for swimming. Any decorations, like driftwood or smooth rocks, should be securely placed. While they are known to uproot delicate vegetation, hardy plants like Java Fern or Anubias attached to decor may survive.

Water quality and movement are paramount. Their high metabolism and active nature correspond to high oxygen needs and significant waste production. This necessitates a robust filtration system, such as a large canister filter or a sump, capable of handling a heavy bioload. The filter outflow should create moderate water movement, simulating the estuarine currents of their natural habitat. Stable, alkaline water with a consistently high level of hardness is required to buffer the pH and mimic their native conditions. Regular, large-volume water changes are crucial to keep nitrate levels low and replenish minerals.

In a community setting, these catfish are boisterous and can be territorial amongst themselves. Keeping them in a proper shoal of at least three, and ideally five or more, helps to spread out any aggression. Tank mates must be chosen with care; they should be other robust, similarly-sized brackish water species that can tolerate the active environment. Examples include larger Monos, Scats, and Archerfish. Any fish small enough to fit in the catfish's mouth will likely be viewed as food. Their omnivorous diet should be varied, including high-quality sinking pellets, wafers, and a mix of frozen or live foods to ensure balanced nutrition.

Ariopsis seemanni is a member of the family Ariidae, commonly known as sea catfishes, which are distinguished from many other Siluriformes by their adaptation to saline environments. The species exhibits a fusiform body shape, an evolutionary morphology that minimizes drag and is ideal for sustained, active swimming in the water column, consistent with its habitat in river channels and coastal estuaries throughout Central and South America. Taxonomically, it is classified within the Actinopterygii class, demonstrating the characteristic ray-finned structure.

Physiologically, A. seemanni is a euryhaline species, capable of advanced osmoregulation to tolerate a wide salinity gradient, from nearly freshwater to almost full marine conditions. This adaptation is critical for its life cycle, which often involves migration between different salinity zones. Its high metabolic rate, coupled with correspondingly high oxygen consumption, indicates a significant energy requirement to fuel its active lifestyle. In a closed aquatic system, this translates to a substantial bioload, with high rates of nitrogenous waste (ammonia) excretion. Aquarists quantify this with a high bioload factor, underscoring the need for advanced life support systems with high-capacity biological and mechanical filtration.

Ethologically, A. seemanni is a gregarious species that forms shoals. This behavior is a key survival strategy for foraging and predator avoidance. While social, intraspecific aggression can occur, manifesting as territorial disputes within the group, likely to establish a social hierarchy. Its feeding ecology is that of a generalist omnivore, consuming benthic invertebrates, detritus, and small fish, utilizing both the bottom and middle strata of the water column. Its environmental interactions include bioturbation of the substrate ('plant_rooter') during foraging activities.

Reproduction in captivity is exceedingly rare, listed as requiring special conditions. This is because Ariid catfishes typically exhibit complex reproductive strategies, including paternal mouthbrooding. The male incubates a small clutch of very large, telolecithal eggs for an extended period, foregoing feeding. This high level of parental investment is likely triggered by specific environmental cues, such as seasonal changes in flow and salinity associated with migratory patterns, which are difficult to replicate in an aquarium setting. The species is currently listed as 'Least Concern' on the IUCN Red List, suggesting a stable wild population.