Metynnis maculatus (KNER, 1858)

Spotted Metynnis

SynonymsTop ↑

Myletes maculatus Kner 1858

Etymology

Metynnis: from the Ancient Greek μετά ‎(metá), meaning ‘after, beyond’, and

maculatus: from the Latin maculatus, meaning ‘spotted’.

Classification

Order: Characiformes Family: Serrasalmidae

Distribution

This species’ range is unclear with records extending from Guyana to the upper and lower Amazon basins in Peru and Brazil, respectively.

However, it is probably found only in the upper rio Madeira, a major branch of the western Amazon watershed in Bolivia and western Brazil, including its major tributaries the rios Beni and Mamoré, plus the upper rio Paraguai in Brazil.

The majority of records pertain to the rio Guaporé (Río Iténez in Bolivia), the main affluent of the rio Mamoré, which drains the vast tropical wetland known as the Pantanal, and the upper rio Paraguai, which also has its headwaters in the Pantanal but flows in the opposite direction. The Guaporé and Paraguai are connected due to rising water levels during the annual wet season.

Type locality is ‘Rio Guaporé, Mato Grosso, Brazil’.

Maximum Standard Length

At least 148 mm.

Aquarium SizeTop ↑

An aquarium with dimensions of 180 ∗ 45 ∗ 45 cm or equivalent should be the smallest considered.

Maintenance

Choice of décor is not as critical as water quality and the amount of open swimming-space provided; we have seen very healthy-looking specimens being maintained in completely bare set-ups for example.

That said, a set-up decorated with a sandy substrate, driftwood roots and branches, and perhaps some water-worn rocks and boulders would provide a more natural-looking spectacle. Aquatic plants are best omitted since they will almost certainly be eaten.

It is intolerant of organic waste and require spotless water in order to thrive. Moderate levels of dissolved oxygen and water movement are also recommended, meaning additional powerheads, pumps, etc., should be employed as necessary, while weekly water changes of 30-50% should be considered mandatory.

Water Conditions

Temperature: 20 – 28 °C

pH: 5.0 – 7.5

Hardness: 18 – 215 ppm

Diet

Metynnis spp. are omnivorous opportunists feeding on invertebrates, smaller fishes, algae, fruit, nuts, aquatic and terrestrial plants.

In the aquarium, offer regular meals of live and frozen foods‚ along with good quality dried products and plenty of vegetable matter. Shelled peas, blanched courgette, spinach and chopped fruit all make good additions to the menu. Larger specimens will also take chopped earthworm, prawn, mussel, etc., but take care not to overfeed.

Behaviour and CompatibilityTop ↑

Not usually aggressive but only appropriate for very large tanks containing robust, similarly-sized tankmates. There are plenty of suitable choices including many cichlids, catfishes, cyprinids, and other characins.

It is often found swimming in large schools in nature and some individuals can become skittish or even aggressive if kept in insufficient numbers in the aquarium, meaning a group of six or more should be the smallest considered. You will be rewarded with a much more natural-looking display, plus interesting behaviour from the fish as they interact with conspecifics.

Sexual Dimorphism

Males possess extended anterior anal-fin rays with the fin thus appearing to be notched medially, a dark spot above the pectoral-fin origin, small dark spots in the dorsal-fin, and dark distal margins to the unpaired fins. The ventral portion of the head is orange-red, this being more prominent in nuptial individuals.

In females the anal-fin margin is straight and the additional aspects of colour pattern are lacking.

Reproduction

Unrecorded in aquaria. This species has been introduced to the Lajes reservoir, southeastern Brazil, where it was found to exhibit an opportunistic reproductive strategy characterised by a long reproductive period, repeated spawning of relatively small batches of tiny eggs, and a relatively small adult body size.

NotesTop ↑

Following the most recent diagnosis by Zarske and Géry (1999), M. maculatus can be distinguished from congeners by the following combination of characters: relatively small scales, with 110-127 in the midlateral series; relatively few gill rakers (20-23); 15-16 branched dorsal-fin rays; relatively short occipital crest, fitting 3-4 times in the distance between its base and the dorsal-fin base; short adipose-fin, measuring 10.7-15.0% SL; colour pattern comprising small, approximately circular dark spots about the same as the pupil in diameter, most pronounced in the ventral portion of the body, sometimes absent.

It is most often confused with the congeners M. argenteus and M. lippincottianus, but can be told apart from both by possessing 110-127 midlateral scales (vs. 98-104 in M. argenteus, 80-95 in M. lippincottianus), and 38-41 spines on the ventral keel (vs. 29-37 in M. argenteus and M. lippincottianus). It is further distinguished from M. argenteus by possessing 13-15 (vs. 1517) branched dorsal-fin rays.

The most recent phylogenetic analyses of the family Serrasalmidae suggest that Metynnis is included in the ‘piranha’ clade alonsgside the genera Serrasalmus, Pristobrycon, Pygocentrus, Pygopristis and Catoprion, and that it may be the basal member of this assemblage.

References

1. Kner, R., 1858 - Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Mathematisch-Naturwissenschaftliche Classe 32(22): 163-168
   Zur Familie der Characinen. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften.
3. Cope, E. D., 1878 - Proceedings of the American Philosophical Society 17(101): 673-701
   Synopsis of the fishes of the Peruvian Amazon, obtained by Professor Orton during his expeditions of 1873 and 1877.
4. Gomes, I. D., F. G. Araújo, R. J. Albieri, and W. Uehara, 2012 - Tropical Zoology 25(1): 2-15
   Opportunistic reproductive strategy of a non-native fish, the spotted metynnis Metynnis maculatus (Kner, 1858) (Characidae Serrasalminae) in a tropical reservoir in south-eastern Brazil.
5. Pavanelli, C. S., R. P. Ota and P. Petry, 2009 - Neotropical Ichthyology 7(2): 141-146
   New species of Metynnis Cope, 1878 (Characiformes: Characidae) from the rio Paraguay basin, Mato Grosso State, Brazil.
6. 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.
7. Thompson, A. W., R. Betancur-R, H. López-Fernández, and G. Ortí, 2014 - Molecular Phylogenetics and Evolution 81: 242-257
   A time-calibrated, multi-locus phylogeny of piranhas and pacus (Characiformes: Serrasalmidae) and a comparison of species tree methods.