Alternative name Melanorivulus formosensis.

Costa did not mention this species in his review of all Rivulus in 2011.

Rivulus formosensis is described from the upper Corrente River drainage,
a part of the Paranaíba River drainage of the upper Paraná River basin, central Brazil by Dr. Wilson Costa. It is considered a
member of the Rivulus pictus clade, which is diagnosed by the flank being intense greenish blue, to purplish blue above
anal-fin base in males. It is distinguished from other species of Rivulus by a unique color pattern consisting
of Y-shaped red marks on the flank in males.

Introduction:

Rivulus is a diversified assemblage of aplocheiloid killifishes inhabiting streams and swamps of most Middle and South America river basins.

It is not diagnosed by unique morphological features (e. g., Costa, 2006a), possibly forming a paraphyletic group (e. g., Hrbek & Larson, 1999; Murphy et al., 1999). The about 100 nominal species included in Rivulus are often divided into six subgenera (Costa, 2006a), among which Rivulus that comprises about 30 valid species endemic to the area encompassing the southern portion of the Amazonian forest, the savannas of central and northeastern Brazil, and the flooded lowlands of western Brazil, eastern Bolivia, Paraguay and northern Argentina (e. g., Costa, 1995a, 2005, 2006b, 2007a-e, 2008; Costa & Brasil, 2008).

However, the highest species diversity of Melanorivulus is concentrated in the central Brazilian Plateau, specifically in the highland region drained by the right tributaries of the Paranaíba River and headstreams of the Araguaia River, the Caiapós hills.

As a result of a taxonomic revision combined to intensive field studies, eight endemic species have been recorded for this region: M. litteratus and M. kayapo from the Araguaia River drainage (Costa, 2005, 2006b), and M. illuminatus, M. pinima, (to be contignued.)

Source:

The original manuscript of W. Costa, March 2008.

Keeping and breeding is easy but a tight fitting cover on the aquarium is necessary because their ability to jump, even through the smallest opening, is unbelievable.

This species can, if there is enough space for them, be housed in a tank with more than one male and several females. If separated before and brought together again however, they can be very aggressive towards each other and fight to become the dominant fish. The best way to produce numbers of fry is to put a pair or a trio in a small tank of about 10 litres with a small filter in it or with some aeration. On the bottom of the tank place some peat moss or dark gravel and a floating "mop" to give space for laying their eggs. The fish will, if they are fed a rich variety of live food, spawn during their whole adult life and produce daily between 5 to 15 eggs.

The eggs should be collected by hand and stored for about 14 days in a small container. Eggs are 1.6 mm and amber coloured. It is wise to add an anti fungus to the water you store the eggs in, to prevent fungal attacks.

After hatching the young fry can eat fresh artemia nauplii without any problem. It takes 4 to 5 months to raise them to maturity. Often the males far out number females. For some species this can become a major problem for the breeder, as he has to raise many fry to enable distribution of a few pairs to other hobbyists. Recent personal tests found that lower pH levels during the time of hatching gave a higher percentage of females. To achieve this I used some peat moss that I added to the container with the eggs just before they were ready to hatch. This peat moss also is a good way to prevent eggs from being attacked by fungus.

Their lifespan can be up to 3 years in captivity.

Remarks :

All above info is like the way other members from the Melanorivulus genus act. The species however is not in the hobby yet and so no specific data are available at the moment.

Max. size 0.0 cm.
Dorsal 00.0,
Anal 00.0,
D/A 0.0,
LL scale count (average) 00.0
Pre- dorsal length to % SL – 00.0 %
Depth to % SL – 00.0 %