Petitella georgiae

False Rummy-nose

Etymology

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

The species epithet georgiae honours Gery’s wife Georgie.

Classification

Characidae: Stethaprioninae

Distribution

Native to the Rio Purus in Peru and Brazil, as well as the Rio Negro and Rio Madeira in Brazil.

Habitat

Mainly found in clear water tributaries and small rivers.

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

Prefers dim lighting and will show its colours better over a dark substrate. It looks superb in a heavily planted setup decorated with pieces of bogwood and twisted roots, perhaps with a layer of surface vegetation to further diffuse the lighting.

It can also be kept in an Amazonian biotope setup if you wish. 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. Aquatic plants should not be used. A few handfuls of dried leaves (again beech is good, and oak is also suitable) would complete the natural feel. 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. The lighting should be fairly dim in this kind of setup.

Water Conditions

Temperature: 22 to 26°C (74 to 79°F)

pH: 5.5 to 7.0

Hardness: 1 to 12°H

Diet

Any food offered must be small enough for its tiny mouth. It will take dried foods, but these should be of a small grade or ground down before being added to the tank. For it to develop the best colour and condition a good proportion of the diet should also consist of small live and frozen foods such as Daphnia or Artemia.

Behaviour and CompatibilityTop ↑

It’s a very peaceful species that won’t compete well with boisterous or much larger tankmates. Ideally keep it with other South American species, such as other small tetras, pencil fish, Apistogramma and other 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.

Always buy a group of at least ten 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 quite tricky to breed. You’ll need to set up a dedicated 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 75-80°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 shouldn’t present too many problems. The adults can be removed once eggs are noticed, or in a very heavily planted tank left in situ and fry siphoned from the tank as they’re noticed.

In terms of productivity it’s best spawned in pairs. Under this technique the fish are conditioned in male and female groups in separate tanks, or via the use of a tank divider. 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 in the evening. They should spawn the following morning. If no eggs have appeared after a couple of days remove them and try a different pair.

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’re 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 one of three species commonly sold under the name “rummy-nose tetra”. The commonest of these is the firehead tetra, Hemigrammus bleheri, whilst the “true” rummy-nose is Hemigrammus rhodostomus. All three are very similar in appearance, but can be 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 the 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’re 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-existent 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.

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 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 georgiae is distinguished from its congeners by a long and wide maxillary (vs. very short and round in P. bleheri, and short in P. rhodostomus); single row of premaxillary teeth (vs. two in P. bleheri and P. rhodostomus); dentary with 9–11 teeth with 5 cuspids (vs. 6, with 6 or 7 cuspids, followed by 1 or 2 tricuspidate ones in P. bleheri, and 5–6 with 5 cuspids, usually followed by 4 conical teeth in P. rhodostomus); absence of black spot on lower posterior border of caudal peduncle (vs. present in P. bleheri and P. rhodostomus).

References

1. Géry, J. and H. Boutière, 1964 - Vie et Milieu Suppl. No. 17: 473-484
   Petitella georgiae gen. et sp. nov. (Pisces, Cypriniformes, Characoidei).
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