Rivulus agilae, Hoedeman 1959

History

Alternative name Laimosemion agilae.

Rivulus agilae , described by Hoedeman from small creeks between the Surinam villages of Agila and Berlijn, is widespread in Guyana, Surinam and French Guiana. First discovered by Geay in 1902, Rivulus agilae appears in a wide variety of colouration and body patterns and are closely related to Rivulus geayi and Rivulus cladophorus.
Their habitat is the open savannah region along the coastal belt and they prefer the sunny and half open areas, mostly in “Black water” creeks and the surrounding swamps, usually with a white sandy bottom. They seek the outer boundaries of the creeks and do travel over land to separated pools were they live eating mosquito larvae and other insects.
"Females have a “Rivulus spot” mostly not very distinct. As they age the spot becomes more indistinct eventually shading into several dark blotches. In many locations Rivulus agilae live sympatric with a member of the Anablepsoides urophthalmus group."

In French Guiana populations show, in general, deep red colours on the body and strong black at the caudal lower margin. The sub marginal yellow lower band is often not present and is replaced by the same red colour of the body.

Westerly, in neighbouring Surinam, more blue develops on the body, the yellow sub- marginal lower band in the caudal is often intense and the black margin is less strong. Body shape becomes less elongated if we compare it to their French counterparts.

 
Rivulus (Laimosemion) agilae - male. SU 2003-18 Brokopondo Districkt, Surinam. Image made by F.Vermeulen.
Rivulus (Laimosemion) agilae - female. Timehri airport, Guyana. Image made by F.Vermeulen.

More westerly in Guyana Rivulus agilae has more blue on the body and the black / yellow margins are often missing or subdued. Sometimes the tail fin does not have the yellow and black margins and body colour is more blueish.

Females are always grey- brown but patterns and subdued colour of anal fin often changes with the various populations.

 


Reproduction

Keeping and breeding is easy but a good cover on the aquarium is necessary because of 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 dominant over the others. The best way to produce offspring 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. Place some peat moss or dark gravel on the bottom of the tank and a floating "mop" to give an area for laying their eggs. The fish will, if they are fed a rich variety of life 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 to the water you store the eggs in, some antifungus to prevent fungus developing.

 

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 :

 


Variations
Rivulus (Laimosemion) aff. agilae - male. Mapa Lake-Berbice River, Guyana.(stressed) Image made by F.Vermeulen.
Laimosemion aff. agilae - juvenile male (yelow type) Mapa Lake, Berbice River, Guyana. Image made by F.Vermeulen.
Rivulus (Laimosemion) aff. agilae. Kwakwani Village. Image made by F.Vermeulen.
Rivulus (Laimosemion) agilae - male. Bagne des Annamites 06-05, French Guiana. Image made by F.Vermeulen.
Rivulus (Laimosemion) agilae - male. Montagne Kaw 07-04b French Guiana. Image made by F.Vermeulen.

There are many variations in colour and appearance, even within one population.

Rivulus (Laimosemion) aff. agilae - male. Mapa Lake, Berbice River, Guyana. Image made by F.Vermeulen.
Rivulus (Laimosemion) aff. agilae - adult male. Loo Creek, Demarara District, Guyana. Image made by F.Vermeulen.
Rivulus (Laimosemion) aff. agilae - juvenile male. Loo Creek, Demarara District, Guyana. Image made by F.Vermeulen.
Rivulus (Laimosemion) agilae - female. Bagne des Annamites 06-05, French Guiana. Image made by F.Vermeulen.
Rivulus (Laimosemion) aff. agilae - male. Piste St. Elie, French Guiana. Image made by F.Vermeulen.

Map

 

 


Meristics

Max. size 4.0 cm.
Dorsal 8.0,
Anal 12.0,
D/A 6.0,
LL scale count (average)33.0
Pre- dorsal length to % SL – 71.0 %
Depth to % SL – 18.0 %

   

Literature

Hoedeman, J.J. 1954. Rivulus agilae, een nieuwe Soort van Suriname. Het Aquarium, 24 (9): 203.