The species is endemic to an area encompassing the middle and lower Rio Ribeira de Iguape basin and smaller coastal river basins of São Paulo and Paraná states. Rivulus santensis is distinguished from all other genus species by the caudal fin's color pattern in males. There is a dark grey to black stripe on the fin's dorsal margin, and another stripe which is similar but distinctively wider on the ventral margin. It is similar to Rivulus haraldsiolii by having both the snout elongated and slightly pointed in a lateral view. Rivulus santensis differs from R. haraldsiolii in possessing 16 rows of scales around the caudal peduncle and one or two minute contact organs per scale on the middle portion of the flank in males, in contrast to 14 scale rows and two to seven prominent contact organs per scale.

Keeping and breeding is easy, but a good cover of the aquarium is necessary because their ability to jump, even trough the smallest opening, is unbelievable. If there is enough space for the fishes, this species can be housed in a tank with more males than one only combined with several females. If separated before and brought together again, males can become very aggressive and fight to dominate others. An excellent way to get offspring is by bringing a pair or a trio in a small tank from 10 liters with a small filter in it. Some peat moss or dark gravel at the bottom, diffuse light, and a floating "mop" will give space for laying their eggs. If they get a rich varity of life food, the fish will 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-colored. It is wise to add Acraflavine to the water you store the eggs to prevent fungi from coming up.

After hatching, the fry can eat Artemia nauplii without any problem. It takes 4 to 5 months to raise this species to maturity. Often, the amount of males outnumber the females. For some species, this can become a significant problem for the breeder as he has to raise many young fishes and so become able to distribute a few pairs to other hobbyists. Recent personal tests learned that lower pH levels during hatching gave a higher percentage of females. To achieve this, I use some peat moss to add to the container with the eggs before they are ready to hatch. This peat moss also is an excellent way to prevent eggs from becoming attacked by fungus. The lifespan of most Rivulus (Atlantirivulus) can be up to 3 years in captivity.

Remarks :

Above data are average data for most Rivulus of this size. No data are actual available for this species so far.

Max. size 6.5 cm.
Dorsal 9.0,
Anal 15.0,
D/A 11.0,
LL scale count (average)38.0
Pre- dorsal length to % SL – 77.0 %
Depth to % SL – 20.1 %