Hydrocynus lucius Cuvier, 1816 (with the genus originally spelled as Hydrocyon).
Boulengerella is named after the Belgian-British zoologist George Albert Boulenger (1858-1937).
The species name “lucius” is given because of its similarity in appearance to the northern pike, Esox lucius.
- Order: Characiformes
- Family: Ctenoluciidae
Cuvier designated the type locality of the species as “Brazil”. However, current records suggest that it is found across the central Amazon region in Brazil and the Río Orinoco in Venezuela.
Previously recorded sightings in the Rio Tocantins in Brazil and coastal drainages of the Guianas are believed to be of Boulengerella cuvieri, while reports from the ríos Paraguay, Paraná, and de la Plata in Paraguay and Argentina are likely inaccurate and may actually refer to a different species of Acestrorhynchus.
When describing a species as pelagic, it means that they inhabit the open water, away from the shore or bottom of a body of water. In the case of this particular species, adults are typically found in main river channels and larger tributaries of both white and black water rivers, as well as floodplain lakes.
These types of habitats offer the species ample space to swim freely and access to a variety of prey items, such as smaller fish and insects. The main river channels and larger tributaries also provide a steady flow of water, which helps to oxygenate the water and create a suitable environment for the species to thrive.
Floodplain lakes are formed during periods of high water and can provide an important refuge for the species during times of flooding. The species may also use these areas to breed and raise their young.
It’s important to note that while adults of this species tend to be associated with main river channels and larger tributaries, juveniles may be found in other areas such as backwater lagoons or smaller tributaries.
Maximum Standard Length
The largest specimen on official record measured 420 mm.
This species is not particularly picky when it comes to its environment, although having some surface cover in the form of floating or overhanging vegetation or branches is appreciated.
It thrives in environments with high levels of dissolved oxygen and a moderate degree of water movement, so the use of external filters, powerheads, airstones, etc. is recommended as needed.
Stable water conditions are crucial to the well-being of this fish, so it should never be added to biologically-immature aquariums. Weekly water changes of 30-50% of the aquarium volume should be considered mandatory.
As Boulengerella species are known to be prodigious jumpers, a tightly-fitting cover is essential. It may also be beneficial to cover the back and sides of the aquarium to reduce the chances of the fish swimming into the glass, as it can be skittish, especially in confined surroundings.
- Temperature: 22 – 28 °C
- pH: 4.0 – 7.0
- Hardness: 18 – 179 ppm
This species is an obligate predator that feeds mostly on smaller fish and insects in its natural habitat, but it can adapt well to dead alternatives in captivity.
Smaller specimens can be offered bloodworms, small earthworms, chopped prawn, and similar food items, while adults will accept strips of fish flesh, whole prawns or shrimp, mussels, live river shrimp, larger earthworms, and more.
Insects such as crickets can also be used as food, but it’s best to feed them fish flakes or some kind of vegetable matter to fill their stomachs before offering them to the fish.
Like most predatory fish species, this fish should not be fed mammalian or avian meat such as beef heart or chicken. Some of the lipids in these types of meat cannot be properly metabolized by the fish, which can lead to excess fat deposits and even organ degeneration.
Similarly, it is not beneficial to use “feeder” fish such as livebearers or small goldfish. These carry the risk of parasite or disease introduction, and they do not have a high nutritional value unless they are properly conditioned beforehand.
Behaviour and Compatibility
Peaceful with anything too large to swallow and can be maintained in a community provided tankmates are chosen with care.
Aggressively territorial or highly competitive species should be avoided. The best choices for tankmates are similarly-sized fishes such as Cichla species and larger doradid or loricariid catfishes.
Other surface-dwelling species should also be avoided, although some hobbyists have reported success keeping this fish alongside related Acestrorhynchus species.
This species is not aggressive towards conspecifics, with juveniles in particular exhibiting a marked schooling instinct. Older individuals tend to be more solitary but still group together from time to time. It is best maintained in numbers of four or more.
Given its eventual size and natural behavior, this species is largely unsuitable for home aquariums. We only know of a handful of private aquarists who have the facilities required to house it long-term.
Juveniles and subadults of this species can sometimes be found in the trade, although they are often misidentified as the congener B. maculata.
One distinguishing characteristic of this species is that its entire dorsal-fin base is located anteriorly to a vertical through the anal-fin origin, which sets it apart from all other ctenolucids except B. cuvieri and B. xyrekes.
B. lucius can be differentiated from both B. cuvieri and B. xyrekes by the absence of a dark spot at the base of the median caudal-fin rays. Instead, the membranes of the median rays are dark at the base, forming a series of horizontally-orientated dark patches between the rays.
Additionally, this species lacks a dusky, somewhat diffuse lateral stripe and has randomly-distributed dark spots on the ventrolateral surface of the body, which sets it apart from both B. cuvieri and B. xyrekes. B. lucius possesses 45-46 vertebrae, which differs from B. cuvieri that has 48-49. It also has 98-117 lateral line scales and 62-72 predorsal scales, which differs from B. xyrekes that has 87-94 lateral line scales and 54-63 predorsal scales.
Boulengerella can be distinguished from Ctenolucia, the only other genus in the family Ctenolucidae, by several features, including possession of 87-124 lateral line scales (compared to 45-50 in Ctenolucia), a strongly developed fleshy appendage at the tip of the snout (compared to weakly developed in Ctenolucia), and the absence of fleshy flaps on the lower jaw (compared to presence in Ctenolucia).
Within the order Characiformes, the family Ctenoluciidae is distinguished by several synapomorphic characters, including a tapering body shape, an elongate jaw shape, and possession of many small teeth with curved tips arranged in a single series within each jaw.
Characiformes is one of the most diverse orders of freshwater fishes, with close to 2000 valid species distributed among 19 families. This taxonomical and morphological diversity has historically made it difficult for researchers to resolve genetic relationships, with many genera remaining incertae sedis. In many cases, exhaustive study of individual species is necessary to resolve such problems.
Modern molecular phylogenetic techniques have provided some insight, however. Research published by Calcagnotto et al. (2005) suggested that Ctenoluciidae belongs to a transatlantic, monophyletic clade alongside the families Lebiasinidae and Hepsetidae, with this assemblage forming a sister group to Alestidae. Other researchers, such as Oliveira et al. (2011), have suggested that the family Erythrinidae is also closely related to this grouping, with Hepsetidae and Alestidae being more distant.
- Calcagnotto, D., S. A. Schaefer and R. De Salle, 2005 – Molecular Phylogenetics and Evolution 36(1): 135-153
Relationships among characiform fishes inferred from analysis of nuclear and mitochondrial gene sequences.
- Oliveira, C. A., G. S. Avellino, K. T. Abe, T. C. Mariguela, R. C. Benine, G. Orti, R. P. Vari, and R. M. Corrêa e Castro, 2011 – BMC Evolutionary Biology 11(1): 275-300
Phylogenetic relationships within the speciose family Characidae (Teleostei: Ostariophysi: Characiformes) based on multilocus analysis and extensive ingroup sampling.
- Reis, R. E., S. O. Kullander and C. J. Ferraris, Jr. (eds.), 2003 – EDIPUCRS, Porto Alegre: i-xi + 1-729
Check list of the freshwater fishes of South and Central America. CLOFFSCA.
- Vari, R. P., 1995 – Smithsonian Contributions to Zoology 564: 1-97
The Neotropical fish family Ctenoluciidae (Teleostei: Ostariophysi: Characiformes): supra and intrafamilial phylogenetic relationships, with a revisionary study.