A Red-tailed black shark
The Red-tailed black shark (Epalzeorhynchos bicolor), also known as the Redtail Shark and Labeo bicolor, is a species of freshwater fish in the carp family, Cyprinidae. It is currently extinct in the wild, but common in aquaria, where it is prized for its deep black body and vivid red or orange tail.
The species was endemic to Thailand, and was formerly found in the Chao Phraya basin, but is now extinct in the wild. There is no evidence that collection for the aquarium trade is responsible for the species’ decline, and it is more likely that construction of dams and draining of swamps that took place during the 1970s are to blame.
It can be difficult to determine whether a specimen is female or male, but typically females’ bellies will have a slightly grayish hue, while males are pure black.
In the aquarium
In the aquarium trade tail colors vary, with bright red and orange being the most common. There may sometimes be color in the pectoral fins, and albino forms may be encountered.
pH and water temperature
Recommended aquarium size is at least 45 gallons or 55 gallons. More aggressive redtails require larger aquariums. Redtails are excellent jumpers, so have a tight lid on the aquarium.
Compatibility and personality
Typically aggressive chasers, but will rarely bite or harm other fish. Individual personalities vary greatly – some are calm while others are extremely aggressive and cranky. They are bottom dwellers and like lots of dark hiding places. They get along with other semi-aggressive fish, but they do not like other sharks.
When two redtails are cohabitated together, they have been known to become extremely territorial with one another. One shark will become dominant and will continually chase and harass the submissive shark, preventing it from feeding and resting. This will often result in the death of the submissive redtail shark.
Redtail sharks are considered compatible in some community tanks, although they may chase docile/peaceful fish that present a large target (such as the Metynnis argenteus, or “Silver Dollar” fish). This may be harmless, but could cause a great deal of stress for the pursued fish, sometimes resulting in the death of the stressed fish (though this is rare). Redtails do not typically bite or injure other fish, but they will chase them and try to corner them. They will mostly chase fish away from their territory and then retreat, therefore it is important to ensure that your aquarium is large enough to allow the red-tail some space to call its territory. Aquariums should be at least 45 gallons or larger for a comfortable community. Redtails are bottom dwellers, so it is highly suggested that one does not introduce them into an aquarium with another bottom dweller, as they will constantly pester and harass them. They also should not be introduced to communities containing other shark-like fish.
Red-tails have varying personalities. Some are calm and will prefer to hide within its territory most of the time, while others are very aggressive and will constantly harass other fish. Most have at least a small streak of aggressiveness and will chase other fish once in a while. It is recommended to observe a prospective red-tail before buying it. Thus one can usually tell in a few minutes whether it is overly aggressive or more relaxed. However, this will not always be a good indicator of whether it will be compatible in your aquarium. It depends on what species are in a given aquarium’s community.
Red-tail sharks have also been known to be excellent jumpers, having a tight fitting lid on the aquarium is recommended.