Austrolebias accorsii is described from Bolivia, Santa Cruz department, Rio Grande, upper Mamoré basin. This recording is the first record of the genus Austrolebias at the Amazon basin. Austrolebias accorsii new species is distinguished from other Austrolebias bellottii species group-members, to where it belongs, by the following combination of characters.  Absence of dots or spots on body and fins (vs. presence), absence of bars on body (vs. presence), anal-fin origin between neural spines (13th-14th vs. 5th-11th) in males. Austrolebias accorsii females differ from females of other species of the Austrolebias bellottii species group by the combination of a higher number of anal-fin rays (31-32 vs. 23-30), a color pattern of the sides of body light yellowish-brown, without bars; usually, 1-3 black spots on the anterocentral portion of flanks, surrounded by metallic green spots, black spots of random size and quantity on the posterior portion of the body to the caudal peduncle (vs. White bars, one to sixteen black spots on anterocentral portion of flanks without metallic green spots, absent black spots in the peduncle.

Abstract redescription 2024

Austrolebias accorsii is redescribed based on specimens from type-locality, nearby temporary pools, and other locations within the same hydrologic unit. Additionally, a novel Austrolebias species is described, exclusively found in two temporary waterbodies in “Abayoy”, a unique vegetation type situated in the transitional zone between the Dry Chaco, Chiquitano Dry Forest,

and Pantanal Flooded Savannas ecoregions in southeastern Bolivia, bordering Paraguay, where the last voluntarily isolated indigenous people outside the Amazon in America reside.

Diagnostic characters for both species are presented.Within Austrolebias two species groups are recognized with different morphological characters, geographical distribution, and ecological traits of their habitats. Furthermore, we suggest the usage of median and interquartile range rather than mean and standard deviation to analyze morphometric and meristic data of rivulids, given the typically non-Gaussian distribution of this data.

To breed most Austrolebias, you need a tank with about 10 to 25 liter water in it, a small jar or plastic container of about 10 to 15 cm high, a little bit of well-boiled peat moss, or coco-peat, and a water temperature between 18 and 24 C. It is wise to add a small filter to that tank and change the water regularly for 90 %. Bring one male and, if possible, two or more females in the tank and feed the fishes daily with live food like daphnia, red- and black mosquito larvae, and white worms. Austrolebias does not accept dry food quickly, and also, the prepared cow-heart is not preferred if live food is offered. If possible, breed this genus in larger tanks with more than one pair or trio and give some hiding places if you do so. When breeding with more than one male, you should also provide more than one spawning container. Every male must have one, and you will see they show interesting territorial behavior to attract females into their spawning place.

The male "flinders" around the female, displaying his fins high- up with the most intense colors. As the female is willing to spawn, she follows the male, pressing his head towards the layer of peat, and when the female contact the male's belly, both will dive into the peat layer. This layer should have a thickness of at least the length of the largest animal or, better, some deeper so they can dive entirely into it.

The spawning occurs during the whole fertile life of the fishes, starting at 5 to 6 weeks of age, till they become old and weak or die from the lack of water in their natural environment. This "end-of-life" will be within 8 to 11 months, depending on the temperature. Higher temperatures will trigger more rapid aging.

In the wild, Austrolebias live in colder environments during the wintertime. Temperatures in Uruguay, Paraguay, and Argentina can get very low. Incubation time usually is six weeks if stored at high temperatures ( 25 C.) and more extended if kept at lower temperatures. The development can last five to six months also. So it is wise to check the eggs regularly to see if the eyes inside the eggs are fully developed and the iris is well visible. When "eyed-up," put a part of the peat with the eggs in water at cool (ca. 18 C) temperature. If the fry usually hatches- and swims within a few hours, wet the rest of the peat. After hatching, feed the fry immediately with freshly born Artemia nauplii. A day or so later, I pour the water together with the fry off and place them in a well-filtered tank without any peat moss to grow up. Austrolebias are not used to strong currents, and juveniles can die if turbulence is too strong. The remaining peat will still have eggs inside that are not ready to hatch yet. Re-pack the peat and store it for some extra time. This hatching delay is nature's answer to short rain showers that fill pools only temporarily, followed by another dry period. Such an event would kill the entire population of the species in that area if all eggs were hatched with first rains. These (late) eggs will hatch later, sometimes very much later, and the fishes that were born earlier will eat these youngs.

As stated before, young's are growing fast and will produce their first eggs after 5 to 6 weeks already, if not even sooner. This breeding information applies to most Austrolebias. However, if the above Austrolebias- species have different behavior or extreme adult size, find these adaptions below in this chapter under <remarks>.

Remarks;

In 2024 this Austrolebias was re-described by Drawert & Ergueta.

Max. size 00 mm in males - female smaller.
Dorsal (average, male only ) 00.0,
Anal (average, male only ) 00.0,
D/A (average, male only ) 0.0,
LL scale count (average) 00.0
Pre- dorsal length to SL – 00.0 %
Depth to SL – 00.0 %
Vertebrae count (average) 00.0

Nielsen, D.T.B. & Pillet, D. (2015): Austrolebias accorsii, a new annual fish (Cyprinodontiformes: Rivulidae: Cynolebiatinae) from the upper río Grande basin, Amazon basin, Bolivia.

Drawert H.A., Ergueta C. 2024. Redescription of Austrolebias accorsii (Cyprinodontiformes: Rivulidae) and description of a new species of the genus from the upper Paraguay River basin. Neotrop Ichthyol. 2024; 22(2):e240001. https://doi.org/10.1590/1982-0224-2024-0001