Rivulus scalaris, Costa 2005

History

Alternative name Melanorivulus scalaris.

The type-locality of Rivulus scalaris is a tributary to the upper Rio Sucuruí, part of the the Rio Paraná drainage in Brasil at an altitude of 810 meter above sea level.

The species was first discovered by Gilberto Campo Brasil and Marco T. Lacerda on January 21 1988. Dr. Wilson Costa, B.B. Costa and C.P. Bove, his partner in life, rediscovered the species on January 13 2004. The typeseries are from the 2004 collection. Holotypes and paratypes are deposited in at UFRJ, Rio de Janeiro, Brasil.

The name is choosen to express the pattern on the sides of the male and, subdued, also seen in females. The latin word "scalaris" stands for <stair> and the V- shape oblique pattern of red lines forming blotches like that of the steps of a stair as the describer saw it.

The species is described in the same paper together with 6 other taxa of the Rivulus genus. These are: Rivulus dapazi, R. cyanopterus, R. rossoi, R. litteratus, R. rutilicaudus and R. egens, all members of the sub-genus Melanorivulus.

 
Melanorivulus (Rivulus) scalaris - male. Rio da Prata, Brasil. Image made by F. Vermeulen.
Melanorivulus (Rivulus) scalaris - male and female. Image made and donated by Francisco Falcon, Brasil.
Melanorivulus (Rivulus) scalaris - male. Fieldcode HvdB 14-10. Image made and provided by W.J. Hoetmer, The Netherlands.
Melanorivulus (Rivulus) scalaris - male F1 without red colour. Rio da Prata, Brasil. Image made by F. Vermeulen.

Reproduction

Keeping and breeding is easy but a good cover of the aquarium is necessary because there ability to jump, even true the smallest opening, is unbelievable.

This species can, if there is enough space for them, housed in a tank with more males than one only and several females. If separated before and brought together again however, they can be very agressive to each other and fight to become dominant to others. The best way to have much offspring is to put a pair or an trio in a small tank from 10 liters with a small filter in it or with some airation. On the bottom some peat moss or dark gravel and a floating "mop" to give space for laying there eggs. The fish will, if they become a rich varity of life food, spawn during there 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 1.2 mm and not colored. It is wise, to add to the water you store the eggs in, some acryflavine to provent fungus coming up.

 

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 number of males is far above the number of females. For some species this can become a major problem for the breeder as he has to raise many young fishes and so become able to distribute a few pairs to other hobbyists.

There lifespan can be up to 3 years in captivity.

Remarks :

With a diameter of 1,2 mm the eggs of Rivulus scalaris are smaller than most other Rivulus species.

In the F1 population some of the males did not show their red markings. This however is an exception and natural disorder. (See the image above).


Variations
Melanorivulus (Rivulus) scalaris - male, from Rio da Prata, Brasil. Image made and donated by Dalton Nielsen, Brasil.
 
Melanorivulus (Rivulus) scalaris - male, from Rio da Prata, Brasil. Image made and donated by Didier Pillet, France.

Map
     

Meristics

Max. size 5.0 cm.
Dorsal 11.0,
Anal 13.0,
D/A 7.5,
LL scale count (average)33.0
Pre- dorsal length to % SL – 74.6 %
Depth to % SL – 23.5 %

   

Literature
Costa, W.J.E.M. 2005. Seven new Species of the Killifish Genus Rivulus (Cyprinodontiformes: Tivulidae) from the parana, Paraguay and upper Araguaia River basins, central Brasil. Neotropical Ichthyology, 3 (1). 78, fig. 10.   PDF