Acestrorhynchus falcirostris (CUVIER, 1819)

Big-Eyed Cachorro

SynonymsTop ↑

Hydrocyon falcirostris Cuvier, 1819

Etymology

Acestrorhynchus: from the Greek akéstra (Gr. ἀκέστρα), meaning ‘darning needle’ and rhýnchos (Gr. ῥύγχος), meaning ‘snout’, in reference to the presence of sharp teeth on both jaws.

falcirostris: from the Latin falcatus, meaning ‘sickle-shaped’ and rostris, the Neo-Latin scientific adjective of rostrum, meaning ‘snout’, in reference to this species’ concave upper jaw.

Classification

Order: Characiformes Family: Acestrorhynchidae

Distribution

The type locality is given simply as ‘Brazil’ but this species is widely distributed throughout northern drainages of the Amazon in Peru, Ecuador and Brazil plus the Río Orinoco in Venezuela and various coastal river systems in Guyana, Suriname and French Guiana.

Habitat

Inhabits major river channels and tributaries and often moves into flooded zones during the wet season.

It apparently shows a preference for clear and black water environments as opposed to turbid ‘white’ waters but has been recorded in both.

Other fishes occurring in the Río Orinoco and available in the trade include Corydoras delphax, Platydoras costatus, Baryancistrus beggini, Hypancistrus inspector, Panqolus maccus, Panaque nigrolineatus, Hemigrammus rhodostomus, H. stictus, Hyphessobrycon sweglesi, Paracheirodon axelrodi, Pristella maxillaris, Copella nattereri, Biotodoma wavrini, Heros severus, Mesonauta insignis, Satanoperca daemon and Uaru fernandezyepezi.

Maximum Standard Length

320 – 350 mm SL.

Aquarium SizeTop ↑

Acestrorhynchids are typically very active and extremely fast swimmers so minimum base dimensions in the region of 250 ∗ 90 cm are required for long-term care.

Even juveniles need a significant amount of room since they tend to act skittishly in small tanks and can easily injure themselves by swimming into the glass.

Maintenance

This species is a near-exclusive inhabitant of open water and an excess of cover can actually stress it meaning, substrate aside, the majority of the tank should be décor-free with plenty of open space.

Should you wish to create a natural effect use a sandy substrate, perhaps with a few handfuls of leaf litter and some driftwood branches or roots.

Plants which can grow in sand can also be added as can those which prefer to be attached to solid surfaces such as Microsorum pteropus, Taxiphyllum barbieri or Anubias spp. while lighting can simply be tailored to the plants being used.

If using a deeper tank you could even fill it to 50-70% of capacity and add emergent branches or plants which can look very effective.

A tightly-fitting cover should be used in all cases since acestrorhynchids tend to be powerful jumpers.

Efficient filtration is a must when keeping predatory species due to the amount of waste produced so install one or more external canister filters and/or a sump system, organising the return in such a way that some surface movement is created.

Weekly water changes of 30-50% should be considered mandatory as this species can be sensitive to organic pollutants¡ and swings in water chemistry, and for this reason it must never be introduced to biologically immature set-ups.

Water Conditions

Temperature: 22 – 28 °C

pH: 6.0 – 7.5

Hardness: 18 – 215 ppm

Diet

An obligate piscivore capable of consuming quite large prey in relation to its body size.

Newly-imported specimens may refuse to accept anything but live fishes although most can be weaned onto dead alternatives once they recognise them as edible, and some even learn to accept dried foods.

Like the vast majority of predatory fishes this species should not be fed mammalian or avian meat such as beef heart or chicken.

Some of the lipids contained in these cannot be properly metabolised by the fish and may cause excess fat deposits and even organ degeneration.

Similarly there is no benefit in the use of ‘feeder’ fish such as livebearers or small goldfish which carry with them the risk of parasite or disease introduction and at any rate tend not have a high nutritional value unless properly conditioned beforehand.

Behaviour and CompatibilityTop ↑

Relatively peaceful with anything too large to swallow and can be maintained in a community provided tankmates are chosen with care.

Aggressively territorial or very competitive species should be avoided with the best choices being placid fishes such as Geophagus spp., Acarichthys heckelii, medium-sized doradid or loricariid catfishes and characids from genera like Ctenolucius, Mylossoma or Myloplus.

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, and it’s best maintained in numbers of four or more.

One important point to note is that acestrorhynchids are cannibalistic given the opportunity so if buying a group or adding to an existing school try to ensure that all individuals are of comparable size.

Sexual Dimorphism

Sexually mature females tend to grow a little larger and be deeper-bodied than males.

Reproduction

Apparently courtship and even spawning have been observed in aquaria but no fry raised.

Reports suggest that spawning occurs in midwater with the female remaining stationary while the male swims around her in a ‘figure-of-eight’ pattern.

The eggs are scattered in large numbers and parental care is non-existent.

NotesTop ↑

This species is a member of the putative A. nasutus group of closely-related species within the genus alongside A. nasutus, A. maculipinna and A. isalineae.

These are characterised by possession of two dark, longitudinal stripes, one running from the tip of the snout to the caudal-fin base and the other from the posterior edge of the lower maxilla to the underside of the caudal peduncle.

In A. falcirostris this patterning is present only in juvenile specimens and it’s also distinguishable by its adult size with the other three species retaining the body stripes into adulthood and tending to grow no larger than 100 mm SL.

Menezes’ (1969) diagnosed A. falcirostris using the following combination of characters: 2 spinous and 9 soft dorsal-fin rays; 5 spinous and 18-24 soft anal-fin rays; 14-19 pectoral-fin rays; 8 ventral-fin rays; 140-175 pored lateral-line scales; 30-37 scale rows between lateral line and dorsal-fin origin; 17-22 scale rows between lateral line and anal-fin origin; 30-39 rakers on lower part of first gill arch; opercle with two dark patches separated by a narrow pale strip; an almost round black blotch on the caudal-fin base.

In addition López-Fernández and Winemiller (2003) state that it possesses a black fringe to the posterior edge of the operculum giving it a ‘collared’ appearance.

The remainder of the genus is currently composed as follows:

A. microlepis group: A. britskii, A. grandoculis, A. microlepis, A. minimus
A. nasutus group: A. falcirostris, A. nasutus, A. isalineae, possibly A. maculipinnis
Not assignable to any group: A. heterolepis

The family Acestrorhynchidae appears most closely-related to the Cynodontidae which contains the genera Cynodon, Hydrolycus and Rhaphiodon.

References

1. Géry, J., 1977 - T.F.H. Publications, Inc.: 1-672
   Characoids of the World.
2. López-Fernández, H. and K. O. Winemiller, 2003 - Ichthyological Exploration of Freshwaters 14(3): 193-208
   Morphological variation in Acestrorhynchus microlepis and A. falcatus (Characiformes: Acestrorhynchidae), reassessment of A. apurensis and distribution of Acestrorhynchus in Venezuela.
3. Menezes, N. A., 1969 - Arquivos de Zoologia (São Paulo) 18(1-2): 1-150
   Systematics and evolution of the tribe Acestrorhynchini (Pisces, Characidae).
4. Prettia, V. Q., D. Calcagnottoa, M. Toledo-Piza and L. F. de Almeida-Toledo, 2009 - Molecular Phylogenetics and Evolution 52(2): 312–320
   Phylogeny of the Neotropical genus Acestrorhynchus (Ostariophysi: Characiformes) based on nuclear and mitochondrial gene sequences and morphology: A total evidence approach.
5. 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.
6. Toledo-Piza, M., 2007 - Zoological Journal of the Linnean Society 151(4): 691–757
   Phylogenetic relationships among Acestrorhynchus species (Ostariophysi: Characiformes: Acestrorhynchidae).