Pantaneiro: ‘of the Pantanal’, in reference to the large tropical wetland in Brazil.
- Order: Characiformes
- Family: Acestrorhynchidae
This species can be found in the primary river channels and tributaries, and it has been observed to move into flooded areas during the wet season.
Maximum Standard Length
The largest officially-recorded specimen measured 240 mm.
Acestrorhynchids are known for their highly active and speedy swimming behavior, which means that they require a minimum tank size with base dimensions of around 250 * 90 cm to ensure their long-term well-being. It’s worth noting that even juvenile specimens of this species need ample space as they can become easily frightened in confined areas, and there is a risk of injury if they collide with the aquarium glass.
In their natural habitat, this species primarily inhabits open water, and therefore, excessive cover in the aquarium can actually cause stress. It is recommended to keep the majority of the tank decor-free, with plenty of open space. If a natural look is desired, a sandy substrate with a few handfuls of leaf litter and driftwood branches or roots can be added. Plants that can grow in sand, such as Microsorum pteropus, Taxiphyllum barbieri, or Anubias spp., can also be included, and lighting can be adjusted according to the needs of the plants.
For a deeper tank, adding emergent branches or plants can create an effective look. However, it’s important to use a tightly-fitting cover as Acestrorhynchids are powerful jumpers. Efficient filtration is a must for keeping predatory species due to the amount of waste they produce. It is recommended to install one or more external canister filters and/or a sump system, with the return organized in a way that creates some surface movement.
Weekly water changes of 30-50% are essential as this species can be sensitive to organic pollutants and water chemistry fluctuations. It’s important to avoid introducing this species to biologically immature setups.
- Temperature: 22 – 28 °C
- pH: 6.0 – 7.5
- Hardness: 36 – 215 ppm
This species is an obligate piscivore that can consume relatively large prey in proportion to its body size. Newly imported specimens may only accept live fish initially, but can usually be trained to eat dead or even dried alternatives once they recognize them as food.
It’s important to note that like most predatory fish, this species should not be fed mammalian or avian meat, such as beef heart or chicken. These types of food contain lipids that the fish cannot metabolize properly, leading to excess fat deposits and potential organ degeneration.
Feeder fish, such as livebearers or small goldfish, should also be avoided. Not only do they carry the risk of introducing parasites or diseases, but they also tend to have low nutritional value unless they are properly conditioned beforehand.
Behaviour and Compatibility
This species is relatively peaceful with anything too large to swallow and can coexist in a community tank if tankmates are selected carefully. It’s important to avoid introducing aggressively territorial or highly competitive species. Good choices for tankmates include placid fishes like Geophagus spp., Acarichthys heckelii, medium-sized doradid or loricariid catfish, and characids from genera such as Ctenolucius, Mylossoma, or Myloplus.
Interestingly, this species is not aggressive towards its conspecifics, and juveniles, in particular, exhibit a strong schooling instinct. While older individuals tend to be more solitary, they still group together from time to time. It is recommended to keep this species in numbers of four or more.
One crucial point to note is that Acestrorhynchids are cannibalistic if given the opportunity. Therefore, if buying a group or adding to an existing school, it’s essential to ensure that all individuals are of comparable size.
Sexually mature females tend to grow a little larger and be deeper-bodied than males.
Based on observations of the closely related species A. falcatus, it is believed that spawning in this species occurs in midwater. During spawning, the female remains stationary while the male swims around her in a figure-of-eight pattern. The eggs are scattered in large numbers, and there is no parental care provided.
This species belongs to the putative “A. lacustris group,” which includes closely related species such as A. abbreviatus, A. lacustris, and A. pantaneiro. All of these species are characterized by possessing a blackish, circular-shaped humeral spot, which is located just behind the gill cover. This distinguishes them from A. falcatus, which has a much larger marking shaped like an inverted teardrop.
While several members of this group are occasionally available in the trade, they are virtually impossible to tell apart without knowing the collection data. The specimens shown in the images above were collected in Paraguay, and based on current knowledge, they are tentatively identified as A. pantaneiro.
Recent phylogenetic studies based on morphology and molecular data have been unable to determine the exact relationships within the A. lacustris group and A. falcatus. Together, they appear to form a clade, with the latter being basal and sister to the rest of the group. Acestrorhynchus species cannot always be distinguished based on morphology, and they are also genetically very similar. A detailed revision of the group, using material collected across their distribution range, is necessary to better understand their systematics.
The remainder of the genus is currently divided into the following groups: A. microlepis group (including A. britskii, A. grandoculis, A. microlepis, and A. minimus), A. nasutus group (including A. falcirostris, A. nasutus, A. isalineae, and possibly A. maculipinnis), and those not assignable to any group (including A. heterolepis).
The Acestrorhynchidae family appears to be most closely related to the Cynodontidae family, which includes the genera Cynodon, Hydrolycus, and Rhaphiodon.
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