Nothobranchius foerschi Wildekamp & Berkenkamp, 1979

Last updated 20/10/2000

 

foerschi: (Latin adjective) = Dedication name in honour of Dr. Walter Foersch, München.

First Description

Wildekamp, R. H. & H. O. Berkenkamp - 1979 - "Nothobranchius foerschi spec. nov., ein aquaristisch bekannter, jedoch wissenschaftlich neuer Prachtgrundkärpfling aus Tanzania, Oost-Afrika (Pisces, Cyprinodontidae)" - Deutsche Killifish Gemein. - Journal 11 (11): 145-157.

Terra Typica

Soga near Dar-Es-Salaam, Tanzania, 38°49'E - 6°43'S; some 45-km west of Dar-Es-Salaam; "in a densely with vegetation overgrown pool in a sisal farm, which dries out several months per year".

Meristic Data

D= 18-..; A= 17-..; 25+1 scales along mid-lateral series;

Synonyms

Nothobranchius species "Dar-Es-Salaam"; Tanzania
Nothobranchius palmqvisti "Dar-Es-Salaam"; Tanzania
Nothobranchius foerschi "Bagamoyo" TAN 95/13; Tanzania
Nothobranchius foerschi "Soga" TAN 97/45; Tanzania (Wildekamp, Watters & Cooper's collection of 1997)

Nothobranchius foerschi belongs to the N.palmqvisti-group, mainly consisting of medium sized species. It has been known to the hobby since 1957 but was then often distributed under the erroneous name of "N.palmqvisti".

Holotype

(SMF 4356) Male with total length of 28.2 mm and standard length of 22.0 mm, imported by Fa Tropicarium (Frankfurt) from Soga near Dar-Es-Salaam, Tanzania.

Paratypes

Code

foe

Size

Males reach a total length of maximum 55-mm, females remain in general some 15-20 mm smaller.

Distribution & Habitat

In a recent past, it was thought that the distribution area of this species was restricted to the original collecting site and its immediate vicinity around Soga, about 45 km West of Dar-Es-Salaam. It is being found there in the typical Nothobranchius pools within the forested East African coastal savannah.

In 1957, Tropicarium Frankfurt imported a fish, which originated from the vicinity of Soga. The fish got distributed under the name N.palmqvisti. It is only in 1979 that Wildekamp & Berkenkamp described properly the species. At several occasions, G. Eggers and L. Seegers searched for N.foerschi in and around Soga but with limited success. Other hobbyists as well had limited success in trying to identify the original collecting site of the species. After the large rainy season, in July 1981, Eggers, Ch. Kasselmann and W. Scholl visited again the Selous Game Reserve, which is then rich in temporary pools and marshes.

During a late afternoon, they discovered in a pool, about 150-m wide and 80-cm deep, with only a very limited amount of open water and overgrown with numerous grass bushels, adult specimens of N.foerschi. Only males could be caught and only along the roadside together with N.melanospilus, a species that occurs in almost any water body in the area. The bottom soil was humid and the water rather hot. Females were only found on the other side of the pool. However, Watters, Wildekamp, and Sainthouse (1995) dispute this discovery, as there has been no verifiable matérial from this locality [neither photographic evidence nor preserved specimens available].

Figure 5: Collecting sites of N.foerschi in Tanzania

 

In June 1995, Wildekamp, Watters and Sainthouse collected N.foerschi from the Ruvu River area near Bagamoyo [TAN 95/13]. Citing Sainthouse (1996c:107), "Passing through Bagamoyo and taking the road leading to the ferry across the Ruvu River estuary, we drove on an earthen embankment. The land on either side was a flat grassy plain covered with coarse grasses and scrubs, making it difficult to dip the net into the water". They collected N.melanospilus, N.janpapi and N.foerschi living together in the same waters. "Until it can be proven otherwise, the collection between Bagamoyo and the Ruvu River ferry can thus be regarded as being the first confirmed collection locality for this species" (Wildekamp, Watters and Sainthouse, 1995). Quoting Sainthouse (1995: 141) the location TAN 95/13 corresponded to "roadside pools and flooded grassy areas on the floodplain of the Ruvu River, a few kilometres from the ferry terminal west of Bagamoyo".

Another Nothobranchius was found at this locality [TAN 95/13]. At least there was a suspicion that it was another species. There was some similarity to N.foerschi but it differed in that it had feint vertical lines on the sides of both male and female. This barred fish, then known as N.spec. Bagamoyo TAN 95/13, was later described as N.annectens by Watters, Wildekamp and Cooper in 1998.

In 1997, Wildekamp, Watters and Cooper collected also three different Nothobranchius species from the Soga TAN 97/45 locality. One was Paranothobranchius ocellatus, the second was N.janpapi and the third N.foerschi. The authors believe that this last locality could represent the original collection site for N.foerschi.

Colour Description

Male specimens display a beautiful light to deep-red tail fin, which is being surrounded on its rear end by a tiny yellow or golden to whitish marginal band. The gold-yellow pectoral fins present on their distal part a remarkable light blue to whitish marginal band. Dorsal and anal fins are gold-yellow and present numerous small deep-red spots, which are being distributed in more or less concentric rings along the fin base. The main body colour is light blue, somewhat more iridescent towards the dorsal-side; this ground colour is being interrupted by a remarkable reticulation pattern formed by the red to dark red borders composing the scale margins. The eye displays a bright iridescent light blue coloration.

Female specimens present, just like their male counterparts, a shortened, non-elongated body shape which give them the appearance of very robust fishes, which they are in Nothobranchius terms. The body colour is grey to greyish-brown with a much lighter belly side and faint golden reflections. Towards the rear-end of the body, the scales present fainted dark grey borders. The pared fins are colourless to light brown. The anal fin is in general gray to gray-brown.

Maintenance & Breeding

Nothobranchius foerschi lives in temporary pools densely covered in vegetation and sometimes in small rivulets, which can dry-out entirely once to twice a year. Therefore, the fishes can best be kept in an aquarium with dense vegetation, which provides at the same time numerous hiding opportunities to the females, which are constantly being followed by the males. The size of the tanks will or course be in relation to the number of fishes being kept, but can seldom be too large.

Often one maintains the sexes separated in smaller tanks and brings them together for a group spawning for short periods of time (one to two weeks). One can also keep females together with only one or two males, which are being changed very regularly in order to secure a correct exchange of genes in the population. Several males can be brought together provided there is a dense vegetation cover and/or when sufficient hiding possibilities have been introduced into the tank. Males are in general not very aggressive towards each other but like to display, as most Nothobranchius species do. Many breeders maintain this species in a 1:2 or 1:4 [or even more] ratio, in the advantage of females, what in fine benefits the females and the reproductive behaviour because they are less subject to stress and less disturbed by males.

Just like the other representatives of the genus, the species responds badly to the presence of Oödinium. The addition of salt [1 teaspoon per 10 litres of water] will surely not reduce the need to regular water changes, but will improve the general condition of the fishes. This seasonal fish requires a strong diet composed of mosquito-larvae (red and black), small worms and fruit-flues.

N.foerschi can perfectly be kept in a temperature range between 20-24°C [ 68°-74°F] , by which the life expectancy of the fishes will be increased. Cooler water [< 20°C or < 68°F] makes the fish sensitive to all kinds of other diseases. Maintenance temperatures ranging between 24-27°C [ 74-81°F] have been mentioned in literature [Kadlec (1991)] but this reduces the life span of the fish. Considering that metabolic processes in N.foerschi are very high, it very much appreciates a regular change of aquarium water.

For reproductive purposes, tanks of 10-20 litres are already large enough. The spawning medium (and by some breeders the bottom cover as well) consists of a 2-3 cm thick layer of peat moss [ a 5 to 10 mm thick peat layer is in most cases already more than sufficient]. In such a tank, one can already breed with a trio or better, with a small group of fishes [2 males and 4-6 females]. The animals are well fed during the breeding period. After a stay of one to two weeks in such an environment, the females need to be put to rest and can be changed with a batch of new ones. Well pre-conditioned females can lay per week between 50 and 100 eggs [Kadlec (1991)]. The 0.95-mm large eggs are being deposited on the peat-moss litter and can easily be recognised with the naked eye. Breeding can also be done in a permanent set-up.

Every week, the peat-moss containing eggs is being removed and replaced by new one, and filtered over a fine meshsize net. The peat-moss is then laid to dry-up for of few days on a kitchen-paper sheet; the substrate with the eggs will however have to remain humid, in such a way that when gently pressed no water drops will come out. At a temperature of 21°-23°C, the eggs will be completely developed after 2-3 months of "dry-but-humid" conservation. At lower conservation temperatures, and with a wetter peatmoss, the development time of the eggs will increase. At 25°C, conservation time can be reduced to 70 days [Kadlec (1991)].

Certain breeders wet the developed eggs with fresh (rain) water of 16-18°C [ 61-64°F] . Most hobbyists however use normal middle hard water from a properly functioning parent tank that has been brought down to 18° and even 20°C [ 64-68°F] . In order to avoid that floating dry peatmoss covers too much of the hatching water surface, the peatmoss with the developed eggs is first poured into a one litre recipient. Water is being added and the whole mixture is being gently stirred and properly mixed for a few minutes so as to permit developed eggs to sink to the bottom; the mixture is then allowed to rest for a few minutes and the floating peat is subsequently removed by hand. The bottom residue is finally poured into the hatching container. Wetting can either take place in an open flat, 5-8 cm high, tray or in a small tank (10x10 or 20x20 cm). The water level at wetting time will have to raise 5-6 cm above the peatmoss. Higher water levels at wetting time (up to 10 cm) usually have no negative effect on the hatching process or rate provided the eggs are at the right hatching stage. I usually hatch the eggs at nightfall and by early morning most of the fry are swimming in the open. Hatching time usually take-up only a few hours (2-4).

Considering that at times, N.foerschi produces only a limited amount of "long-resting-eggs", it usually doesn't pay to re-dry the peatmoss once again. The freshly hatched fry are relatively small but can immediately handle Paramecium. This food-type is offered during the first two days, afterwards one can offer Cyclops- and Artemia-nauplii. If the offered Artemia strain produces small nauplii, these can be given strait away. From now on, feeding has to be continuous and plenty in order to secure steady grow. With regular water changes, a large tank and with plenty of food at their disposal, the fry grows fast. After 6-8 weeks, they can reach maturity [according to Kadlec (1991), it would be possible that, with adequate feeding, sexual maturity is reached after only 1 month]; after four months, the fry is adult. After 6-7 months some ageing processes start to appear when kept at higher temperatures (27°C) and after 8-9 months when kept at about 20°C.

Recently, Lee Harper reported (KillieTalk, 21-XII-98) to have incubated some 50 N.foerschi eggs in water in a Petri dish with just a trace of acriflavine. After about a week, he changed the water with new non-acriflavine water. After 15-days of water incubation at 21°C [70°F], most of the eggs had disappeared (Harper assumed they might have been destroyed by Cypris present in the Petri dish), 7 embryos were partially developed and 5 had hatched and were perfectly normal. They normally hatch in 6-8 weeks in peatmoss at similar incubation temperatures. With this experience, Harper questioned whether N.foerschi was a real annual. Harper reported further on another observation, where two batches of N.foerschi eggs were maintained, this time without Cypris, one in a Petri dish and a second batch in a vial. After 2 weeks of water incubation, the eggs in the Petri dish showed significant embryo development. Those in the vial did not. He therefore assumed hat oxygen content in the water is essential to embryo development.

Bellemans (1999) reported that in their natural environment the embryologic development of N.virgatus eggs was halted by anaerobic soil conditions appearing a few hours after egg-fertilization. This, combined with the pool dessication process, itself linked to substantial bottom-mud contraction, which strongly encloses the eggs, created an oxygen deficient environment in which the eggs could not develop. He observed that after about 6 months of resting all 50+ 'mud-encapsulated' eggs he could find were still in diapause I. He showed that it is only when the first rain weakens and swells again the mudcrust that oxygen can again reach the resting eggs through micro-faults in the mudcrust. He further observed that it is only then that embryologic development to the stage of resting embryo (diapause II) started. This latter process was accomplished in a very short time for those eggs having access to oxygen as the first rain mostly occurrs when air temperatures are at their hotest, just before and during the first rains.

It would thus appear that water incubation of Nothobranchius eggs is surely possible in most if not all species, provided eggs are kept in an oxygen rich [water flow of oxygen rich water over or through the spawning medium] environment from just right after ferilization. In case of an oxygen deficient environment just after fertilization, the embryoligic development of the eggs is halted in diapause I. However this constitutes an unnatural environment for annual fish as, in their natural environment, such eggs may be induced to develop and hatch during the same rainy season, jeopardazing the survival success of the entire next generation.

Bibliography