Nothobranchius orthonotus (Peters, 1844)

Latest update 21/12/99

orthonotus:

First Description

Terra Typica

The first collecting site of this species was reported from near Quelimane, on the mouth of the Zambezi in Mozambique. The entire distribution area comprises probably the entire drainage system of the lower Zambezi, reaching southern Malawi, the area of the Pungwe, Sabe, Limpopo, Pongola and Mkuze rivers, from south-eastern Zimbabwe (Gona-Re-Zhou National Park) to north-eastern Southern Africa (Krüger National Park).

 

Figure 1: Distribution of N.orthonotus in southern Zimbabwe

 

Figure 2: Distribution area of N.orthonotus in southern Africa

 

Meristic Data

According to Jubb (1975)

Scale counts: Lateral line series 28-30, 24-28 around the body in front of the ventrals; 4 rows of scales on cheeks below orbit, 4-5 rows on head between orbits;

Fin counts: Dorsal fin: 15-16 rays; anal fin: 14-17; ctenoid spines on rays. Origin of dorsal fin over origin of anal fin. Insertion of dorsal fin midway between origin of middle rays of caudal fin and posterior edge of preoperculum.

Teeth: As illustrated by Peters, upper and lower jaws with outer and inner rows of spaced, relatively large. sharp, hooked teeth, with numerous scattered, small pointed teeth between these rows. Mouth large, directed upward.

Karyotype:

Synonyms

Cyprinodon orthonotus Peters, 1844
Hydrargyra maculata Peters, 1855 (in Jubb, 1975)
Fundulus othonotus Günther, 1866 (in Jubb, 1975)
Nothobranchius othonotus Peters, 1868 (in Jubb, 1975)

Populations in the hobby

N.orthonotus "U-3" [no longer available]
N.orthonotus "U-7" [no longer available]
N.orthonotus Pongola 'blue', South Africa [Vermaak]
N.orthonotus 'rouge' Krüger National Park, South Africa
N.orthonotus
MW 88/11 = MW 91/8, Malawi [Watters & Woodford]
N.orthonotus MW 91/9, Malawi [Watters & Woodford]
N.orthonotus MW 91/10, Malawi [Watters & Woodford]
N.orthonotus Pongola N92/1

Holotype

 

History

{According to Jubb 1975}

During the years 1842 to 1848, Dr. Wilhelm Peters of Berlin, explored the Zambezi River, one of the largest rivers in southern Africa, from its mouth to as far inland as Tete, a small town some 400-kilometres upstream established by Portuguese Dominican Fathers as far back as 1531. In addition to birds and reptiles, Peters collected many fishes, most of them new to science, from the Zambezi fresh and estuarine waters.

The Zambezi River runs into the Indian Ocean via an extensive delta of ever-changing channels and floodplains subject to seasonal flooding. One of the most stables of these channels is the Kwakwa or River of Quelimane, which enters the sea about 95 km north of the other mouths of the Zambezi. West of Quelimane, there are low-lying seasonal swamps and it was from these swamps that Peters obtained the first specimens of a fish species which, today, is referred to as N.orthonotus. He would have landed at Quelimane and must have obtained this specimen soon after this as in 1844 he published a short description of his material under the name Cyprinodon orthonotus.

In 1855 Peters, for reasons not stated, listed his material in another scientific journal as Hydrargyra maculata. The specific name "maculata" meaning spotted is, as will be seen later, of great significance. In 1866, A. Günther, of the British Museum, in his 'Catalogue of the fishes in the British Museum', transferred Peters' Cyprinodon orthonothus to the genus Fundulus. That same year Günther and Playfair, in their publication 'Fishes of Zanzibar' referred some specimens of Nothobranchius from Zanzibar to the species orthonotus, but in 1893 these were described by G. J. Pfeffer as a new species with the name Fundulus guentheri.

In 1868, Peters published his "Reise nach Mossambique" in which, with meticulous care and thoroughness, he described and illustrated the fishes he collected in the Mozambican waters. To accept the species orthonothus, he erected a new genus, which he named Nothobranchius. In his amended description of N.orthonotus, Peters gave the distribution area as ranging from the freshwater swamps near Quelimane to Quisanga, some 850-km northwards up the coast of Mozambique. Peters also included the record of Günther and Playfair of orthonotus from Zanzibar. In his discussion, he recorded that the vernacular name was Anamolugo and added "Gebacken gibt er vortreffliches Gericht" meaning "baked they provide an excellent dish".

For some unknown reason ichthyologists continued to refer their material to the genus Fundulus instead of using Peters' Nothobranchius.

However, in 1924 George S. Myers, recognised the genus Nothobranchius but also erected a new genus Adioniops with guentheri as the type species to accept guentheri, neumanni and other related species. But in 1933, Myers, in a paper with the title "The genera of the Indo-Malayan and African Cyprinodont Fishes allied to Panchax and Nothobranchius" published in Copeia, wrote as follows:

"Recent study has convinced me that Ahl was perfectly correct in referring Fundulus neumanni, Fundulus guentheri and other related forms to Nothobranchius. Fundulus kunthae Ahl and Adiniops troemneri Myers, both from Beira, appear to be identical with N. orthonotus. Peters' types of orthonotus, one of which I have examined, were in poor condition and the lips are flabby and stretched. This makes the specimen I have examined [just as in Peters' figure] seem to have a great lateral gape. I find that the lips when placed in their original position are like those of guentheri. Nothobranchius orthonotus has, however, longer jaws than any other Nothobranchius but I cannot separate it generically on this character alone."

Colonel J.J. Scheel's classic "Rivulins of the Old World", published in 1968, left no doubt about the confusion that existed in the common and scientific nomenclature of Nothobranchius species. It was decided, therefore, in the first instance, to try and establish the identity of Peters' Nothobranchius orthonotus.

Apart from the emended description of Nothobranchius orthonotus published by Peters in 1868, available literature, both popular and scientific, has provided little additional evidence as to the identity of this species. A type specimen obtained on loan by courtesy of the Berlin Museum confirmed the thoroughness of Peters' emended description but added little to our knowledge of the appearance and colour pattern of the living fish.

Attention had to be turned to the type locality Quelimane and the possibility of obtaining fresh material from that part of Mozambique. However, the first live specimens of Nothobranchius that could be identified as representing orthonotus came from isolated pans in the northern parts of the Krüger National Park, near the Mozambican border. DR. U. DE V. Pienaar discovered these fish. This was followed by specimens of Nothobranchius orthonotus from elephant drinking pans in the Gona re Zhou Game Reserve in the in the low-veld near the Rhodesia [presently Zimbabwe] and Mozambique border.

In March 1968, R.E. Furzer and Dr. W. Warne were looking for fishes in southeastern Zimbabwe [ex-Rhodesia] in one of the greatest bodies of water known as Sazale, which along with many others forms part of the Guluene river system. They collected N.orthonotus, an unknown species of Nothobranchius, and the lungfish, Protopterus annectens.

Mr. B. Donnelly, a Rhodesian Fish Research Officer on vacation, collected specimens from pans on the flood plains of the Pungwe river near Vila Machado. Then final confirmation of this research work on the exact identity of N.orthonotus came from a large collection of Nothobranchius from the Lower Zambezi River system made by Mr. S.M. Grant.

Grant's collection was made near Chiromo on the flood plains of the Shire River, a tributary of the Zambezi which is the only exit of Lake Malawi, Africa's third largest lake. From an ecological point of view, the lower Shire and lower Zambezi areas, including Quelimane, all belong to one large ecosystem subject to seasonal flooding, during the summer months, and dry spells extending from autumn to early spring.

Meristic and morphological studies have shown that Grant's specimens, like those of the other collectors mentioned above, represent Peters' Nothobranchius orthonotus. Grant's collection is particularly valuable as it is supported by colour photographs and notes on the living fishes in their natural habitat. As far as vivid colour is concerned, Nothobranchius orthonotus is the least attractive of the known Nothobranchius species. The maximum size attained by mature males varies with the habitat and population density, but under optimum conditions male specimens of up to 100 mm in total length have been recorded.

Size

Males usually reach a total length ranging between 60 and 90 mm (U. de V. Pienaar, 1978), but records of specimens of up to 100 mm have been reported (Jubb, 1975).

Females usually remain smaller.

According to Him (1995), the males of the Malawi MW 88/11-population reach only 50 mm whilst these females reach only 40 mm length.

Code

ORT

Distribution & Biotope

The distribution of N.orthonotus is given as the tropical East Coast lowlands of Africa (Crass, 1964; Turner, 1964; Jubb, 1965, 1967 and Bell-Cross, 1976).

Fowler (1934) described a killifish, Fundulus mkuziensis, which had been collected by Bell-Marley from the Mkuze River during 1931. This species is currently accepted as a synonym of N. orthonotus, although Jubb (1969) expresses doubt about the synonymy, because of some character overlap between N.(mkuziensis) and N. rachovii Ahl, 1935 (Kok & Walley, 1978).

Other records of N.orthonotus from Natal [South Africa] include:

According to Jubb (1978), the known distribution area of N.orthonotus reaches from the swamps west of Quelimane, the floodplains of the lower Zambezi River in Mozambique to the floodplains of the lower Shire River system in Malawi, the floodplains of the Pungwe River, where it is found syntopically with N.rachovii. It is also found in seasonal pools in the Gona-Re-Zhou Game Reserve in southeastern Zimbabwe, where it occurs syntopically with N.furzeri and towards the south in temporary pools in the Krüger National Park in northeastern South Africa. Finally it is also found in the floodplains of the Pongolo River, in Kwazulu, in northern Natal, South Africa (Jubb, 1978). According to Jubb (1978) N.orthonotus is a very variable species, which in the future could possibly fall into several different under-species. He however preferred to consider it as a polytypical species, with different forms of appearance.

Walley, collected six mature adult N.orthonotus [two males and four females] on 16 April 1977 from Ngwema pan (Kok et.al., 1978). These have been housed in the Albany Museum, Grahamstown (AM/P 4035-4041). The females were only partly spent and specimens ranged from 62-52 mm SL, the largest being a male. The dimorphic sexual characteristics were the same as those given for the species by Jubb (1967, 1969). Ngwema pan [2714'S, 3216'E] is an ephemeral roadside pool lying above and to the east of the Pongolo floodplain in Tongaland. It dried up completely during the winters of 1974, 1975, and only partially during 1976. Kok sampled this pan and the Pongolo floodplain pans extensively on several occasions during these three years but captured no N.orthonotus. The sudden "re-appearance" of these fishes was attributed by Kok and Walley (1978) to their embryonic diapause which arrests ontogeny even over several seasons, as an adaptation to their erratic environment as shown by Wourms (1972) for N. guentheri, N. palmqvisti, and N.melanospilus. Alternatively, Pienaar (1968) discussed the possibility of Nothobranchius eggs being transferred in mud on the legs of wading birds.

According to U. de V. Pienaar, (1978), N.orthonotus are real annual fish in the sense that they complete their entire life cycle within a period of one calendar year. An isolated colony of N.orthonotus was discovered in 1960 by U. de V. Pienaar, (1978) in a temporary pool in the headwaters of the Mtomene river in the Lebombo mountain range, close to the border between Transvaal and Mozambique [2417' S - 3157' E]. This population was originally found during the rainy season, on 24th February 1960, and the fish were fully-grown adults. A second population was subsequently discovered in a small pan on the international bondary at Pumbe picket [Krüger National Park - South Africa]. These are the only records of naturally occurring N.orthonotus within the Krüger National Park, and in the Transvaal, but they are also known from pans in northern Zululand, and in the lowlands of southern Mozambique (U. de V. Pienaar, 1978).

According to U. de V. Pienaar (1978), "the pools on the eastern boundary of the Krüger National Park hold water only for a few months during the rainy season and dry up completely. Occasionally they are not filled at all, and they are nowhere deeper than about 1 meter. The depressions usually fill with the first heavy summer rains in November or December. Subsequent visits during February have proved that by that time, the newly hatched fishes have already attained adult proportions. The pH of the water here was 6.7, thus considerably more acid than the waters in rivers and pools elsewhere in the Park. A water analysis provided the following results: Solids in parts per million - 145 (i.e. 38 parts Sodium, 7 parts Calcium, 6 parts Magnesium, substances causing temporary hardness 2.3, chlorides 59, sulfates 2, bicarbonates 4 and fluorides 0.25). The pools have a muddy substratum of deep black clay, which is derived from rhyolite".

"During the summer seasons of 1963-64 and 1966-67, and repeatedly during the period 1971-1978, severe floods inundated the area in which our N.orthonotus habitats are situated. As a result of the massive run-off of floodwaters, considerable erosion of the topsoil was evident in this area. The small Mtomene River ran very strongly, and the floodwaters eventually reached the larger tributaries of the Nwanedzi River, draining the Lebombo flats in this area. Other fish species, such as catfish Clarias gariepinus and several small Barbus spp. [B. trimaculatus, B.toppini and B.(Beirabarbus) radiatus] migrated up these tributaries and eventually invaded the Nothobranchius habitat. Some fear for the survival of this isolated colony was experienced, particularly as no killifish were found here at all during some of these critical periods" (U. de V. Pienaar, 1978).

"It would appear, however, that these fishes have an ingenuous survival mechanism which ensures that the population is not eliminated by natural catastrophes such as those mentioned above.... It would also appear that eggs do not hatch if the pH and salinity of the water in the pond does not dry up before the life cycle of the fish is completed. In situations where the pool is not filled to a safe level, or when only the top layers of mud are moistened, the eggs will not hatch. If the temperature of the water is too high, the eggs will not hatch either. That some of these mechanism are at work was proven by the fact that N.orthonotus was again found in numbers in the Mtomene pools during summer seasons of 1964-65" and those following the bad floods in the early seventies (U. de V. Pienaar; 1968, 1978).

 

Figure 3: Original and new habitats of N. orthonotus in the Krüger National Park - South Africa
- [After
U.de V. Pienaar, 1978]

 

U. de V. Pienaar (1978) further mentions that "on,20th April 1975, a number of N.orthonotus were netted in the pools below the Mtomene habitat and released in the pan at Pumbe beacon and in a pool in the headwaters of the Nhlangulene spruit of Nwanedzi section. At a later stage, on 26th April 1976 about 80 of these rare fishes were captured in the pan at Pumbe picket and transported by helicopter to the northern Nyandu sandveld where 15-20 were released in the two Nwambiya pans and a further 20 odd in the Machayi-pan [Figure 3]. Subsequent surveys during March 1977 and February 1978 established the successful colonization of both the Nwambiya pans and the captured fishes were very large (80-90 mm in length) and in excellent condition" (U. de V. Pienaar, 1978).

According to U. de V. Pienaar (1978), the diet of these fishes consists primarily of mosquito larvae, together with small crustaceans and other tiny aquatic organisms.

P. la Hausse de Lalouvière (1986) mentions that Kok and Walley (1978) recorded the killifish N.orthonotus, considered by Skelton (1977) as a vulnerable species, from two areas of the floodplains of the Pongolo River; the north-west [Ndumu Game Reserve] and the south-east [Nhlanjane and Ngwema]. Despite intensive sampling in the pools of the Ndumu Game Reserve, Ngwema pool and Lake Nhlanjane, no further specimens were found there between 1982 and 1985. Ephemeral rainpools throughout the floodplain area were fished during this period, mostly without success. However, a further four ephemeral pools in the south-east floodplain area close to Madonela [2721'S-2316'E] at lake Nhlanjane, were found to contain N.orthonotus [Table 1]

Table 1: Collection sites of N.orthonotus [After P. la Hausse de Lalouvière, 1986]

Locality

Distance from Madonela
[2721'S - 3216'E]

Date

Rusi Numbers

(Smith Institute
acquisition number)

Nomathasa

5.5 km N

17 Dec.83

24245,25042,25151,20580

05 Jan.84

-

28 Feb.84

20581

16 Apr.85

-

Engulubeni

17.0 km N

17 Dec.83

20583

08 Aug.84

24719

Empisini

12.5 km N

16 Apr.85

-

Okhayeni

6.1 km N

28 Feb.84

20582

Engodwini

13.5 km WSW

18 Dec 83

24307

Unknown (apparently a tributary of
the
Pongolo river, 6 km E of Jozini)

17.5 km SW

Dec. 83

-

 

Specimens of N.orthonotus were also found in Engodwini [Mlambo], a tributary stream of Lake Mayazela [2723'S - 3208'E]. Mayazela is 8.5 km NE of Jozini and 13.5 km WSW of Madonela and lies west of the Pongolo River. In December 1983, J. Vermaak (pers.comm. to P. la Hausse de Lalouvière) also found N.orthonotus in a small waterbody adjacent to a culvert on the Jozini-Madonela road close to the Makatini Experimental Farm. Most specimens have been lodged in the JBL Smith Institute of Ichthyology (P. la Hausse de Lalouvière, 1986).

"There appears to be a clumped distribution of N.orthonotus in the southern floodplain area, parts of which is currently being put under commercial cultivation. Its absence from previously recorded collecting sites does not preclude its more general distribution in the region, as its reproductive strategy involving embryonic diapause and the requirement for the eggs to dry out before hatching (Jubb, 1981) may be responsible for its erratic appearance at various localities" (P. la Hausse de Lalouvière, 1986).

In 1990, R. Kyle mentioned that there have been several references in literature on the presence of the spotted killifish Nothobranchius orthonotus in Ndumu Game Reserve including Crass 1964, Kok and Walley 1978, Bruton and Kok 1980, La Hausse de Lalouvière 1986 and Skelton 1987. He further mentioned that as far as could be established all these publications referred to one collection by J.E.W. Dixon in early 1964 of which the locality is given as the Pongolo floodplain inside the reserve. Coke (pers comm. to Kyle) gave the exact locality as the headwaters of Nyamithi Pan. Since the original collection, no further specimens had been recorded inside Ndumu in spite of intensive sampling over an extended period (Pooley, 1975; La Hausse de Lalouvière, 1986). R. Kyle reports that this had resulted in the original collection being questioned (Kok, 1980) moreover that it had important implications for the conservation status of the species.

Kyle (1990) reported that on 3 April 1989, several specimens of N.orthonotus were caught in a small isolated pool in a streambed in the west of Ndumu Game Reserve. During follow-up sampling on 5 April 1989, numerous specimens (total length 18-63 mm) were found in several isolated pools along approximately the last two kilometers of the stream, which flows from the southwest into the marsh at N.R.C. Camp. "There had been little rain recorded in the past few weeks at the office in the reserve but there was evidence in the study area of fairly recent heavy rains. With one exception (la Hausse de Lalouvière, 1986) all the previous Natal records were from ephemeral pools and not streams. It is possible that N.orthonotus occurs principally in temporary pools adjacent to this stream but on this occasion, they were flushed into the stream during heavy rains. This hypothesis could account for the lack of previous records, despite the regular flow of the stream each year. No other fish species were found in the pools. Generally this species is found where no other fish species occurr (Skelton, 1987) but they were found in November 1988 in a roadside pool near Balamhlanga pan on the Pongolo floodplain in company with Oreochromis mossambicus and Barbus paludinosus"(Kyle, 1990). The Ndumu records of N.orthonotus serve to confirm its presence in the game reserve and to give a precise locality. The previous record was stated as the Pongolo floodplain whereas this record is the first on the periphery of the Usuthu floodplain. (Kyle, 1990).

Kyle reported that on the October 23, 1987, it was decided at a Tembe Elephant Park management meeting to introduce N.orthonotus into the Park (Kyle, 1993). "The next day one hundred of these fish [20 - 35 mm TL] were caught in a temporary pool [2724'15" S - 3212'00" E] adjacent to Balamhlanga Pan, which is about 10 km north-east of Jozini. They were driven directly to Tembe and released in the Mahlasela Pan system in a small isolated pool [2703'40" S - 3227'08" E] just inside the southern boundary of the park, 3-km east of Sihangwana Camp. The fish were caught using a hand net made from 30% shade cloth and transported in two 60 x 30 cm insulated plastic boxes in 3 cm deep water. The complete operation took approximately two hours and no fish died in transit or appeared to be unduly stressed" (Kyle, 1993).

According to Kyle (1993), "the Mahlasela Pans are a series of temporary pools in a sandy area. Although situated close to the Mosi Swamp drainage they do not make surface contact with any other drainage system even during severe flooding. In spite of intensive sampling no fish have previously been found in the Mahlasela Pans and N.orthonotus had not yet been recorded elsewhere in the Tembe Elephant Park. The introduction was initially of an experimental nature as it appeared desirable to establish N.orthonotus in "safe" localities. The introduction site comprised one isolated pan approximately 70 x 20 m size so that if necessary, the fish could subsequently have been destroyed".

Kyle (1993) sampled the Mahlasela Pan on 14 November 1987 when eleven killifish of 50-65 mm TL were caught and released. During a further sampling on 22 December no fish were found. On 18 November 1988 the pan was revisited and in a short time seven mature N.orthonotus were caught. Since the pan had dried out and refilled between the dates of sampling. The presence of live killifish in 1988 indicated that the translocated fish had spawned successfully.

Kyle (1993) further reports that Skelton (1987) considered N.orthonotus as rare and endangered in South Africa and that "in the Krüger National Park it had been translocated successfully on several occasions since 1975 (U. de Pienaar, 1978). De Moor and Bruton (1988) described the species as usually inhabiting temporary pans on the periphery of drainage systems, these localities usually being isolated from surface drainage lines. They also suggested that translocation of this species was probably desirable because of its rare status, but cautioned that care should be taken to protect the integrity of gene pools. The principal motivation for this introduction into Tembe Elephant Park was the fact that almost the entire area of occurrence of this species around the Pongolo floodplain was under immediate threat both from a large irrigation scheme (Woodburn pers. comm. to Kyle) and from commercial agriculture (La Hausse de Lalouvière, 1987). There were also plans to spray Balamhlanga Pan with a mosquito larvicide (Short pers. comm. to Kyle). Thus the survival of these fish in the Pongolo system was uncertain. The success of this introduction meant that there were several colonies in a game reserve in Maputaland, besides the one reported in Ndumu in the 1960s (Crass, 1964) and which was reconfirmed by Kyle in 1990".

Scheel's "Atlas of Killifish" gives a vague description of the natural collecting sites of this species. It occurs within the Krüger National Park [red-form] and within the flood areas of the Mkuze and Pongola rivers [blue-form]. WOOD visited in 1983 the Pongola-Mkuze areas on 3 different occasions but could not re-capture this species again. Apparently, five months earlier, J. Vermaak found the species in this area.

According to Bowmaker et al. (1978), N.orthonotus would occur in the Buzi and Pungwe rivers, the Limpopo river, the Natal rivers south of the Pongolo to the Umtamvuma River, The Pongolo and Incomati Rivers, the Sabi and Lundi Rivers and the Lower Zambezi River system.

In 1991, Watters and H. Woodsford collected N.orthonotus MW 91/8 in southern Malawi (Watters, 1990).

Description

According to Wildekamp (1977) and Jubb (1978), several populations of this species, differing in colour pattern, can be found. Jubb (1978) speaks of a polytypical species [with several phetotypes].

In de vicinity of Beira, N.kuhntae can almost always be found in company of N.rachovii. According to Scheel (1990), Seegers & Wildekamp (1983) it could appear that N.kuhntae does not constitute a valid species but merely represents a local form of N.orthonotus. N.orthonotus is rather commonly distributed in Southern Africa and is being replaced in Tanzania by N.melanospilus and possibly, more towards the north, by N.elongatus. Also on the island of Zanzibar, one can find that a larger Nothobranchius-species [N.melanospilus] lives syntopic with a smaller one [N.guentheri].

According to U. de V. Pienaar (1978), live adult males from the Krüger National Park are dark iridescent blue-green on the dorsal surface with a paler golden-olive ventral surface. The dorsal and anal fins have deep mauve or indigo edges and magenta-coloured spots. The rays of the anal fin are deep maroon, and the lateral scales are edged with maroon with distinct spots along theirs posterior margins. The iris is golden and the operculum spotted with dark red. In females from the Krüger National Park, the dorsal and anal fins are golden-olive with bluish edges and brown spots.

According to Jubb (1975), the general description is as follows:

Scales: bordered with maroon to red-brown colours; scale centres iridescent sky-blue, turquoise or sea-green, the intensity of body coloration depending largely on circumstances as wild fish under stress are often quite pale;

Dorsal fin: Membrane olive with numerous small red or reddish-brown spots and transverse bands; extremity of fin darkish and often edged with white;

Caudal fin: Membrane dark olive with red or reddish-brown spots. In some specimens the fin rays near the base of the caudal are also red or reddish brown;

Anal fin: Membrane pale olive with numerous small magenta or reddish-brown spots and transverse bands. Extremity of fin mauve or black with white border;

Ventral fin: Small with red or reddish-brown spots and blotches;

Pectoral fin: Transparent and olive membrane with extremity of fin streaked with red or reddish-brown;

Ventral surface: Golden with numerous small red or reddish-brown spots toward the caudal region;

Eye: Iris golden with dark vertical band through eye. In adult males eye small, the diameter going about 5 times into length of head;

Operculum and preoperculum: Iridescent sky-blue or sea-green with scattered, prominent red or reddish-brown spots on cheeks and Operculum, the ventral border of the Operculum being jet black. The spots mentioned above are a prominent feature and remain so for quite a long time after all other body colour features have faded. This colour pattern may have prompted Peters to use the specific name maculata in 1855;

Female coloration: Females of Nothobranchius orthonotus are usually smaller than the males. They are a uniform pale olive colour without any dark spots on the posterior part of the body. This is very important to remember as in the vicinity of Beira, Mozambique, another species of Nothobranchius has been collected, more vividly coloured in the case of males but the females are distinctly spotted towards the caudal region. This species has been assigned provisionally to Nothobranchius kuhntae (Ahl, 1926);

Relationship

N.vosseleri differs from N.orthonotus in having a shorter head (27.4-31.5 % SL, vs. 29.9-33.0), a greater pre-dorsal length (56.2-67.7 % SL, vs. 57.7-62.9), a smaller pre-anal length (52.9-65.4 % SL, vs. 59.0-66.6), fewer dorsal fin rays (14-16, vs. 16-18), fewer scales in mid-lateral series (25-31, vs. 31-33), and male coloration (in N.orthonotus, dominated by a dark red spot pattern on the head) (Wildekamp et al., 1998).

The taxonomic status of the Nothobranchius populations found between the mouth of the Zambezi and the Ruvuma River basin in south-eastern Tanzania is presently not known and they may represent one or more undescribed species related to N.orthonotus and/or N.melanospilus.

Maintenance & Breeding

With this species, the hobbyist has a fish that can be easily be maintained in a company aquarium. However, elderly males can at times, become rather aggressive towards their tank mates. No special requirements are needed as far as maintenance temperature is concerned, provided these do not reach into the extremes (Wildekamp, 1977).

The reproduction of these annual fishes is not very difficult and is already feasible in a 10-15 litre tank (Him, 1995). The spawning medium (well rinsed peat moss) is either spread over the entire bottom or kept together in a small plastic container with a cover into which a large hole is foreseen. The fish will lay their 1,25 mm eggs onto this dark and soft substrate. After a 7-14 days spawning period, the substrate is being removed and left to dry for one to two days. The peat moss with the eggs is then kept, together with sufficient air, into a closed plastic bag until the length of the incubation period for the species has been reached. The incubation period should not be less than 5 months.

Him (1995) mentions an incubation period of 5 to 7 months. Watters (1999) reported that he successfully hatched N.orthonotus MW 91/8 eggs 3 years, 5 months and 2 weeks after spawning. He found a good number of both eyed and cleared eggs in the oldest spawning of this population he had. The next oldest was 3 years, 4 months and had even more eggs, both clear (undeveloped) and eyed. He further mentioned that he regularly hatched N.orthonotus, N.furzeri, N.rachovii, N. sp. Hoba, N. sp. Liwonde, after incubation periods of 1-2 years. But the N.orthonotus MW 91/8 case beat his previous record, which was with N.rachovii KNP black [he hatched a batch of fry of this species from a spawning that was 3 years, 3 months and 2 weeks old]. The two bags in question had never been wetted before nor had they been opened during the entire storage period. The incubation temperature is kept at 25C.

Hatching the fry happens with fresh water [18-20C]), hard or soft, but preferably with a similar composition as the water in which the adult fish laid the eggs. The water height at hatching time can reach up to 4-5 cm. The fry, after having filled the swimbladder, are able to eat freshly hatched Artemia nauplii and can reach, at optimal care, sexual maturity after only two months. Fry appears to be vulnerable to water conditions and require a regular partial water change.

Him (1995) reported sex ratio's for juveniles ranging from more males to a 50/50 ratio.

Literature