Based on current knowledge, it thus remains impossible to deduce whether the group of putative species currently comprising S. jurupari, S. mapiritensis, and S. rhynchitis, plus populations from Amapá and the upper Negro/upper Orinoco region, represent distinct taxa or a single meta-population which can be referred to as S. jurupari sensu lato. Here on SF we include the named species separately, since they continue to be considered valid.

H. borealis is a member of the putative ‘H. heterorhabdus-group’ of closely-related species within the genus as proposed by Géry (1977).

There are around 15 members characterised by a ‘longitudinal pattern’ consisting of a thin, usu…

It’s known by various vernacular names including ‘Pirá-pacu’, ‘Pira-pucu’ or ‘Diente de cao’ (central Amazon), ‘Bicuda’ or ‘Uena’ (rio Tocantins), ‘Bicuda’ (rio Tapajós), ‘Aguejeta’ or ‘Picua’ (Venezuela), and ‘Moruwi’ or ‘Pirapoko’ (Guyana).

The entire dorsal-fin base is located anteriorly to a vertical through the anal-fin origin and this character distinguishes it from all other ctenolucids except B. lucius and B. xyrekes.

In a study conducted on the Arataye River, the main tributary of the Approuage, this species was mostly collected from stretches of rapids with rocky substrate which were reduced to a series of pools during the dry season. Other fishes observed at the same site were Auchenipterus nuchalis, Hypostomus gymnorhynchus and Moenkhausia cf. intermedia while at other localities in the river Bryconops affinis, Myleus ternetzi, M. rhomboidalis, Moenkhausia aff. barbouri, Curimata sp. and Serrasalmus sp. were collected.

This species occurs alongside the similar-looking congener C. oiapoquensis in nature, from which it can be told apart by the following combination of characters: larger adult size; narrower body (body breadth fits 4.0-4.4 times in standard length vs. 3.4-3.8 times in C. oiapoquensis); shorter pectoral spine (3.4-3.8 times in SL vs. 2.7-3.2 times); longer snout (1.7-1.9 times in SL vs. 2.0-2.2).

This is the type species of the genus Aequidens and has the widest distribution of any member species. It exists in various colour forms depending on locality with variants from Ecuador and Peru being particularly sought after since they develop striking red (Ecuador) or orange (Peru) colouration on the lower part of the jaw, head and anterior portion of the belly whereas those from Brazil tend to have an overall grey/blue/green colouration, for example.

Despite its type status it's long…

This species is uncommon in the aquarium trade although its name is sometimes applied to other species.

It was originally described in the monotypic genus Pseudopristella, and can be distinguished from the vaguely similar Pristella maxillaris by possession of a relatively large (vs. relatively small) humeral spot and having black pigmentation in the anal-fin restricted to the first ray (vs. a prominent distal blotch).

This small species is a popular aquarium fish but there is some confusion surrounding its identity. Two colour forms have been traded, one of which also possesses tiny hooks on the fin rays.

It can be distinguished from congeners by colour pattern; the body is rose-coloured, fins red with no black markings, and the ovoid humeral spot is prominent, measuring around half of the body depth.

Metynnis lippincottianus is occasionally seen for sale, sometimes under the name of "Silver Dollar". It is easily distinguishable from m. argenteus and m. hypsauchen (which are more commonly sold as Silver Dollars) by its spotted pattern, hence the common name. M. lippincottianus shares a common name with m. maculatus but the two can be distinguished as the spots on m. maculatus are more pronounced.

Silver dollars are common and popular fish in the hobby. They are related to piranh…

Given its eventual size and natural behaviour this species is largely unsuitable for the home aquarium, and we know of only a handful of private aquarists with the facilities required to house it long-term.

Unfortunately juveniles are readily available in the trade, although the scarcity of privately-maintained adults would suggest that most fail to reach their potential.