Alternative name Laimosemion nicoi.

Rivulus nicoi was found in October 1989 by Leo Nico at the right bank of the Rio Ventuari, Amazonas Territory in Southwest Venzuela. Rivulus nicoi was found in company with an, at that time new species of annual fish, and was described in the same paper with this annual fish named Pterolebias xiphoporus by Jaimie Tomerson & Donald Taphorn. (later renamed and transferred in a new genus as Micromoema xiphophorus (Costa) and in Micromoema xiphphora by Seegers in 2000)

Both species were collected in a temporary pool about 500 meters inland from the right bank of the Ventuari river some 5,5 km upstream from the piont the Yureba river enters the Ventuari.

The authors did have only 5 juvenile alcohol specimen of this new species of this new Rivulus to their disposal and saw long pectoral fins as one of the most remarkable differences to other species of this genus. No detailed colours in life are described but it was mentionned by Leo Nico the species showed blue colouration on the body. Both sexes did show a "rivulus" spot. This however is very common in Rivulus in their first stage of life and does not implicate both sexes will show these spots also in their adult stage of life. Also the fact that the species was found together with a confirmed annual was reason for the describers to suggest this Rivulus species could be a semi-annual too as result of their ocurrence in a annual biotope. They quoted the species was "a not confirmed annual" however.

It was my goal in (April 2012) to collect life fishes again from the terra typica to learn more about this species and its behaviour. This expedition was one of the most challenging ones so far as travelling to that spot had to take place under extreme circumstances on the Orinoco- and Ventuari river and the outcome was unsecure as April is the dry season while the species was discovered in October 1989 which was during the rainy season. To reach the spot we needed to make a boat trip of over 350 km upriver and 350 km downriver also to return to the basecamp at Puerto Ayacucho. There is no other way to get to it. The rivers will be low and the annual habitat will be dried out completely, but on the other hand the Rivulus will survive somewhere in remaining creeks and swamps nearby I believe. We succeded to get near the terra typica and re-collected the species which was a real wonder and a big achievement of the whole team.

This is a very strange Rivulid fish species. The fishes act like bellysliders while mating. Male and femal dwell along the bottom and put their eggs at the bottom only. If a mop is available they do not use it. Best is to put a layer of peat and forest leafes on the bottom where they will spawn. Egg get covered with peat particals and difficult to find. The eggs are ambercolored and a bit stcky. The first eggs were collected around december 2012 and these eggs stayed in diapause for 6 months. Only one fish hatched and became an adult male in about 6 months after the day of emerging. It is clear that this species is a unique annual fish. Storage in water with some trypaflavine is resulting in the loss of most of the eggs. Storage on peat also gives losses but less. If peat is rather moist it seem things go better..many eggs are waiting for their full development at the end of 2013 as I write this....and only one fish still after all the waiting. To be contignued....

Remarks :

This is the first record of breeding this fish ever.

Max. size 3.0 cm. ( adult size not known)
Dorsal 8.4,
Anal 12.8,
D/A 5.4,
LL scale count (average)27.2
Pre- dorsal length to % SL – 74.1 %
Depth to % SL – 20.2 %

Thomerson, J.E. % D.C. Taphorn. 1992. Two new annual Killifishes from Amazonas Territory, Venezuela (Cyprinodontiformes: Rivulidae). Ithyol. Explor. Freshwaters, 3 (4): 380, fig. 4.

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