The elegant predatory tetras of the genus Boulengerella are divided into 5 species: B. cuvieri, B. lateristriga, B. lucius, B. maculata and B. xyrekes. They are widely distributed in the large river systems of the Amazon and Orinoco and the Guyanas. Distinguishing the species is not easy, especially with small juveniles. Juveniles of B. cuvieri differ from their relatives in that the lower caudal fin lobe is considerably larger than the upper one. Very small animals (4-5 cm) still have the ancient extension of the spine as the upper edge of the caudal fin. This quickly disappears; from a total length of approx. 6 cm you can recognize the species-typical caudal fin structure with a smaller upper and larger lower caudal fin lobe. B. cuvieri retain their dark cloudy juvenile coloration up to a total length of approx. 10 cm. Then the species-typical adult coloration appears with a light back, a chocolate-colored longitudinal band in the middle of the body and a silvery belly. There is then a small spot on the root of the tail. With increasing age, the caudal fin turns a strong orange-red color. Other typical characteristics of B. cuvieri are the strangely shaped anal fin, the rearmost rays of which are so long that they protrude beyond the base of the caudal fin, and the dorsal fin, which is set far forward.
All Boulengerella species can be easily distinguished from about 10 cm in length. B. lateristriga is the only species with a striking black and white striped caudal fin. B. lucius and B. maculata are almost identical in color, both are dotted on the body and have an irregular spot/striping in the caudal fin, but in B. lucius the dorsal fin sits much further towards the head on the back, so that an imaginary vertical line from the end of the dorsal fin towards the ventral edge comes out well before the base of the anal fin (the same applies to B. cuvieri), whereas in B. maculata it is in the middle of the anal fin. At 10 cm in length, B. xyrekes looks a little like a small juvenile of B. cuvieri, but in B. xyrekes both caudal fin lobes are about the same size and the rearmost anal fin rays end well before the base of the caudal fin.
Boulengerella cuvieri is the largest species of the genus. It can grow to a record size of almost 1 m long and weigh 6 kg. The species has a huge distribution area in South America and is found practically everywhere in the Amazon and Orinoco basins and in the Guyana countries. Imports mostly come from Peru, Venezuela and Colombia. The predatory tetra inhabits various types of water in its native area, but is most frequently found in fast-flowing waters, where it lurks for prey behind obstacles such as rocks and tree trunks. As a rule, it stays below the water surface and is an excellent jumper (cover the tank well). When keeping them in an aquarium, care should be taken to ensure that they are kept as stress-free as possible, as otherwise uncontrolled flight reactions may occur. The animals easily bump into the walls of their tank and can injure their sensitive mouths. As fish eaters, they should be fed with live or frozen fish. It goes without saying that they should only be kept with fish of the same size, as small inhabitants are regarded as food. The animals are peaceful with each other and like to be in the company of conspecifics.
For our customers: the animals have code 210403 (approx. 10 cm) on our stock list. Please note that we only supply the wholesale trade.
Text & photos: Frank Schäfer
