Hemigrammus rhodostomus

Rummy-nose tetra

SynonymsTop ↑

Hemigrammus rhodostomus (Ahl, 1924)

Etymology

Petitella Géry & Boutière 1964, from the French –ella, a diminutive connoting endearment; in honor of zoologist-anatomist Georges Petit (1892-1973).

rhodostomus, derived from the ancient Greek rhodo-, meaning red or rose; and Ancient Greek stoma, meaning mouth; referring to the red nose and mouth area.

Classification

Characidae: Stethaprioninae

Distribution

Rio Orinoco and the lower Amazon basin in Venezuela and Brazil.

Habitat

Blackwater rivers and tributaries. The water in these biotopes is typically stained brown with tannins from decaying organic material and is very acidic as a result.

Maximum Standard Length

2″ (5cm).

Aquarium SizeTop ↑

This is a species that should be maintained in groups numbering 10 or preferably more, and its active swimming nature requires a tank length of 36 inches/90 cm minimum.

Maintenance

A biotope setup would be very simple to arrange. Use a substrate of river sand and add a few driftwood branches (if you can’t find driftwood of the desired shape, common beech is safe to use if thoroughly dried and stripped of bark) and twisted roots. A few handfuls of dried leaves (again beech can be used, or oak leaves are also suitable) would complete the natural feel. Aquatic plants are not a feature of this species‘ natural waters. Allow the wood and leaves to stain the water the colour of weak tea, removing old leaves and replacing them every few weeks so they don’t rot and foul the water. A small net bag filled with aquarium-safe peat can be added to the filter to aid in the simulation of black water conditions. Use fairly dim lighting. Under these conditions the true beauty of the fish will be revealed.

Alternatively, it also does well in a more standard, well-planted tank. A good maintenance regime is essential with this species as it will lose colour in unfavourable conditions. Weekly partial water changes are therefore a must.

Water Conditions

Temperature: 76-80°F (24-27°C)

pH: 5.5-7.0. Its colours will become faded if kept in alkaline conditions.

Hardness: 2-15°H

Diet

Omnivorous and will accept just about anything offered. It does have a small mouth, though, so correspondingly-sized foods are best. Feed a mixture of dried flakes and granules and small live and frozen foods. A varied diet such as this is essential for the best colour development.

Behaviour and CompatibilityTop ↑

It’s a very peaceful species that won’t compete well with very boisterous or much larger tankmates. Ideally, keep it with other South American species, such as other Hemigrammus or Hyphessobrycon species, pencil fish, Apistogramma dwarf cichlids, Corydoras and small Loricariids. In a more general community it can be combined with smaller rasboras, barbs, Anabantoids and West African dwarf cichlids such as Pelvicachromis species. Many discus enthusiasts keep a shoal of rummy noses in their show tanks, too.

Always buy a group of at least 10 of these, preferably more. They are one of the more tightly shoaling small tetras, and will not do well if kept in insufficient numbers. Because they do shoal so closely, they actually look far more effective when maintained like this anyway.

Sexual Dimorphism

Mature females are noticeably rounder in the body than males.

Reproduction

Can be bred in a similar way to other species in the genus. You’ll need to set up a separate tank if you want to raise decent numbers of fry. Something around 18″ x 10″ x 10″ in size is fine. This should be very dimly lit and contain clumps of fine-leaved plants such as java moss or spawning mops, to give the fish somewhere to deposit their eggs. Alternatively, you could cover the base of the tank with some kind of mesh. This should be of a large enough grade so that the eggs can fall through it, but small enough so that the adults cannot reach them. The water should be soft and acidic in the range pH 5.5-6.5, gH 1-5, with a temperature of around 80-84°F. Filtering the water through peat is useful, as is the use of RO water. A small air-powered sponge filter bubbling away very gently is all that is needed in terms of filtration.

It can be spawned in a group, with half a dozen specimens of each sex being a good number. Condition these with plenty of small live foods and spawning should not present too many problems.

Alternatively, it can be spawned in pairs. Under this technique, the fish are conditioned in male and female groups in separate tanks. When the females are noticeably full of eggs and the males are displaying their best colours, select the fattest female and best-coloured male and transfer them to the spawning tank. Contrary to much that has been written this species spawns exclusively in the evening

In either situation, the adults will eat the eggs given the chance and should be removed as soon as eggs are noticed. These will hatch in 24-36 hours, with the fry becoming free swimming a 3-4 days later. They should be fed on an infusoria–type food for the first few days, until they are large enough to accept microworm or brine shrimp nauplii. The eggs and fry are light sensitive in the early stages of life and the tank should be kept in darkness if possible.

NotesTop ↑

This is the ‘real’ rummy-nose. The species most often sold as such is, in fact, the firehead tetra, H. bleheri. These 2 are very similar in appearance, as is the ‘false’ rummy-nose, Petitella georgiae. The 3 species can distinguished by several factors.

The first, is by the extent to which the red colouration on the head of the fish extends into the body. H. bleheri is the only one of the 3 in which the red extends beyond the gill covers. The amount of red colouration on the other 2 species is similar, although it tends to be a little lighter in tone in P. georgiae. This factor alone cannot be used to positively identify a species, though, as if the fish are not in good condition, the red colour can fade considerably. This is particularly true for H. bleheri.

The second thing we can examine is the caudal peduncle of the fish. All 3 species possess a dark blotch at the top of the caudal peduncle, but only the Hemigrammus possess one at the bottom. If the bottom blotch is absent, you are probably looking at a Petitella.

The third factor to look at is the line extending laterally from the central caudal fin band into the body of the fish. This is quite broad in P. georgiae, narrower in H. rhodostomus and almost non-exisitent in H. bleheri. By a combination of these factors, you should be able to identify your fish. The species differ in a couple of other ways, too, such as the patterning of the caudal fin and at the base of the anal fin. Obviously, they can also be distinguished by fin ray and scale counts, but the methods described here should suffice for most hobbyists.

Like all Hemigrammus, the taxonomic status of this species is currently Incertae Sedis, meaning uncertain. The genus is currently used as something of a catch-all for over 70 species of small characin. Most experts agree that a full revision is required, with the likely outcome that many species will be placed into new or different genera.

Bittencourt, et al. (2020) proposed the transfer of the rummynose tetras Hemigrammus rhodostomus and H. bleheri to the genus Petitella on the basis of molecular and morphological data. Petitella is defined therein as follows:

The genus Petitella is readily distinguished from all remaining characid genera by the possession of a distinctively bright red head, the presence of a black horizontal bar that extends from the end of the caudal peduncle to the middle rays of the caudal-fin, and the presence of an oblique black bar in each caudal-fin lobe, separated by white colored bands. Contact between frontals anterior to frontal fontanel present; posterodorsal margin of ethmoid cartilage and lateral ethmoids distant from lateral ethmoids; 17 or fewer branched anal-fin rays; only one or two anal-fin hooks on each ray of adult males; the presence of parallel longitudinal ridges on the posterior field of scales; scales covering one-third of the length of caudal-fin lobes; coloration of the head distinctively red, especially the snout.

The phylogenetic reconstruction also confirms Petitella georgiae as a sister-group of Petitella bleheri. The striking p-distance divergence (9.1%) between the Peruvian P. georgiae and our samples from the Purus River indicates the possibility of Petitella georgiae being a species complex. The monophyly of P. bleheri and P. georgiae was highly supported in our analyses — the first time Petitella georgiae was included in any molecular phylogeny — as well as by the morphological data of Mirande (2019), who reported seven morphological synapomorphies supporting the sister-taxon relationship between these two species.

Petitella rhodostomus is distinguished from its congeners by the red head color not extending to the humeral region and the presence of a black spot on the lower posterior border of the caudal peduncle (vs. head color not extending to humeral region with only one black spot on caudal peduncle in P. georgiae, and head color extending to humeral with two black spots on caudal peduncle in P. bleheri); dentary with 5–6 teeth, with 5 cuspids, usually followed by 4 conical ones (vs. 9–11 teeth, with 5 cuspids in P. georgiae, and 6 teeth, with 6 or 7 cuspids, followed by 1 or 2 tricuspidate ones in P. bleheri).​

Bittencourt, et al. 2020 changed the species epithet rhodostomus to rhodostoma, but the specific name is an indeclinable noun and thus remains rhodostomus (Eschmeyer’s Catalog of Fishes, 2020).

References

1. Ahl, E., 1924 - Wochenschrift für Aquarien- und Terrarienkunde v. 21 (no. 18): 405
   Ueber eine farbenprächtige Neuheit, Hemigrammus rhodostomus E. Ahl. sp. n.
2. Bittencourt PS, Machado VN, Marshall BG, Hrbek T, Farias IPF, 2020 - Neotropical Ichthyology 18(2): e190109
   Phylogenetic relationships of the neon tetras Paracheirodon spp. (Characiformes: Characidae: Stethaprioninae), including comments on Petitella georgiae and Hemigrammus bleheri.
3. Mirande, JM, 2019 - Cladistics 35(3): 282-300
   Morphology, molecules and the phylogeny of Characidae.