Alestes
Alestes Müller & Troschel, 1844
Body elongate and silvery. In some species, the fronto-parietal fontanel remains wide open, even in adults. Swim bladder extending posteriorly beyond the anus into the caudal peduncle. Dorsal fin with two simple and 7-9 branched rays beginning at or behind level of pelvic fin insertions. Eye covered with a very well-developed adipose eyelid. Six teeth in the outer premaxillary row; dental formula (for both jaws): 6-8/8-2. All species exhibit a pronounced sexual dimorphism affecting the shape of anal fin which is convex in adult males and straight or concave in juveniles and females.
Type species: Alestes dentex
Salmo niloticus Geoffroy Saint-Hilaire, 1809 [= Alestes dentex (Linnaeus, 1758)] by subsequent designation of Jordan, 1919.
Currently, six species are assigned to the genus Alestes.
Key to species
1 31-33 scales along the lateral line............................................................................ A. inferus
More than 35 scales along the lateral line.............................................................................. 2
2 45 to 60 gill rakers on lower limb (ceratobranchial) of first gill arch........................A. stuhlmannii
At most 41 gill rakers on lower limb (ceratobranchial) of first gill arch.........................................3
3 At least 30 gill rakers on lower limb (ceratobranchial) of first gill arch.......................A. baremoze
At most 27 gill rakers on lower limb (ceratobranchial) of first gill arch..........................................4
4 Rayed dorsal fin origin distinctly behind pelvic fin insertion...........................................A. dentex
Rayed dorsal fin origin at about the same level as pelvic fin insertion..........................................5
5 Anal fin with 14-16 branched rays.......................................................................A. liebrechtsii
Anal fin with 17-20 branched rays...............................................................A. macrophthalmus
Alestes baremoze (de Joannis, 1835)
Types and type localities
Myletes baremoze Joannis, 1835: 31, pl. VI. Type locality: “Thèbes sur le Nil (Egypte)”. Syntypes MNHN n° A. 9712
Alestes kotschyi Heckel, 1849: 308, pl. XXI fig. 4. Type locality: “Assuan, Egypt”. Syntypes: NMW 16630 (1, dry), 66687 (2)
Alestes wytsi Steindachner, 1870: 542, pl. II, fig. 1. Type locality: “Dagana, Bakel, Senegal, western Africa ». Syntypes: (several) ?MCZ 4008 (4); NMW 76206 (2), 54790 (4), 54793 (7), 66755-73 (4, 5, 8, 4, 2, 5, 2, 3, 4, 4, 3, 2, 2, 2, 2, 4, 2, 5, 2)
Alestes splendens Werner, 1906: 1127. No designated type
Alestes baremoze tchadense Blache, 1964: 74-78, fig. 30. No designated type
Synonyms
Salmo niloticus (non Hasselquist) Linnaeus, 1766
Cyprinus dentex (non Hasselquist) Linnaeus, 1766
Salmo dentex (partim) Linnaeus, 1766
Myletes baremoze Joannis, 1835
Myletes hasselquistii (non Cuvier) Guérin, 1844
Alestes kotschyi Heckel, 1849
Alestes wytsi Steindachner, 1870
Alestes baremose Boulenger, 1901
Alestes splendens Werner, 1906
Alestes baremoze Monod 1950
Alestes baremoze tchadense Blache, 1964
Common names
Arabic: Kawara baladi/Meloha, Rashala/Rie (Sudan)
Dinka, Northeastern: Alerio/Cin/Lang ager/Nyadiaar (Sudan)
El Molo: Nyele (Kenya)
English: Characin/Silversides (Ghana), Egyptian robber (KenyaPebbly fish
Estonian: Siig-mölderkala
Ewe: Asenti/Asentiwoe (Ghana)
Finnish: Hohtoalesti/Siikatetra
French: Péré (Niger)
Fulfulde, Pulaar: Giccal (Senegal)
Ga: Tewe (Ghana)
Guro: Klawôlè (Cote d'Ivoire)
Hausa: Mazari/Shemani (Nigeria)
Ijo: Oza (Nigeria)
Kanuri: Kaya (Nigeria)
Kim: Vaï/Van/Vore (Chad)
Limba, west-central: Ba-borah (Sierra Leone)
Mende: Konguy (Sierra Leone)
Not specified: Delete,Juse,Lelete (Kenya)
Nubian: Girfiga (Sudan)
Nuer: Cien (Sudan)
Nupe: Egbagi (Nigeria)
Nyoro: Angara (Uganda)
Shilluk: Kodo (Sudan)
Soninké: Saara (Senegal)
Themne: A-gbantan (Sierra Leone)
Turkana: Dorobela (Kenya)
Wolof: Sèlinthe (Senegal)
Yoruba: Arefe (Nigeria)
Zande: Basongirino (Sudan)
Description
Diagnosis: 38-51 scales in lateral line, 7½-9½ above, and 3½ below lateral line. Anal fin with three spines and 19-28 soft rays; 30-41 gill rakers on lower limb of first gill arch; 41-49 vertebrae. Dorsal-fin origin distinctly behind level of pelvic-fin insertions.
Maximum reported size: 325 mm SL (440 g) in West Africa, 425 mm in Lake Turkana.
Colour: sides uniformly greyish, back greyish-blue, belly white. Fins generally greyish, but lower caudal-fin lobe orange in Sudan populations; caudal fork finely edged with black. No precaudal or humeral spots.
Affinities: A. baremoze is very closely related to A. dentex, with which it can easily be confused, since these species are sympatric. It is distinguished from that species by its lower body depth, the greater number of branched anal-fin rays (23-26 against 19-23), and especially, the much higher number of gill rakers on lower limb of first gill arch (30-41 against 18-27).
Alestes baremoze: main morphological characters of the types.
Alestes baremoze: number of anal fin rays.
Alestes baremoze: number of lateral line scales.
Alestes baremoze: number of vertebrae.
Alestes baremoze: anal fin rays mean number and lateral line scales mean number in different African basins.
Growth
The abundance and the economic interest of this species lead numerous authors to study its biology and especially its growth ; Niger (Daget, 1952), Lake Turkana (Hopson, 1975), Lake Chad (Durand, 1978) and Bandama (Paugy, 1978).
All agree in saying that the growth rate is higher in females which therefore reach bigger sizes. On the other hand, results show quite different growth according to the geographical regions. Their length decreases progressively from Lake Turkana to Bandama and Niger, via Chad, given the same age criteria.
For the four studied basins, the maximum reported lengths obviously vary in the same proportions to the growth curves (see figure below).
Alestes baremoze: growth for males and females in four different African basins.
Reproduction
In Niger River(Daget, 1952) as well as in Côte d'Ivoire (Paugy, 1978), individuals reach their sexual maturity at the end of their second year in river systems. On the other hand, in lake Chad (Durand & Loubens, 1970) and in lake Turkana (Hopson, 1975), it is only reached at the end of the third year
However, Durand (1978) observed that the sexual maturity was reached by the end of their second year when Lake Chad levels were dropping and believes that in this case, "the small Chad" phase was associated with a simple widening of River Chari.
Thus, it seems that depending on the environment (fluvial or lakeside), there is an adaptation of sexual maturity age. According to Daget (1957), Sudan species, such as A. baremoze, need high temperatures to begin gamete maturation. It is really around April, when water temperature reaches its maximum (30°C) in Sudan regions, that gonad maturation is induced.
The spawning period takes place between July and September, during the rise in the river level. This season is more favourable for the young as a result of the presence of floodplains that provide them with plenty of food.
Nevertheless, we note that the annual cycle of spawning is preserved in Côte d'Ivoire, where rivers do not often overflow their banks.
Some information about spawn modalities of A. baremoze have been collected in Chad (Durand, 1978). Females ready to spawn are located, not in floodplains, but at low water levels in full flow.
The stock of eggs is spawned in one go at the end of the afternoon. Finally, we have to notice that mature individuals do not gather in large groups during spawning period and that they are scattered among immature ones.
A. baremoze belongs to high fecundity species. This fecundity is approximately the same whatever the regions where the studies are carried out.
The results we give correspond to a mean fecundity per kilogramme of female body weight:
Higher fecundity has been observed in the Nile (Nawar & Yoakim, 1963), but these results still have to be confirmed.
Diet
The diet of A. baremoze is not very strict. In reality, like a lot of species, it seizes any available food. As Lauzanne (1976) noted, the species feeds mainly on plant and insect matter in the rivers although in the majority of the lakes it feeds clearly on zooplankton.
As well as the supply of endogenous food, we must not neglect the supply of exogenous food, mainly constituted by terrestrial insects or imago of aquatic larvae. Finally, a few authors report that fish remains have been found in some stomach contents (Greenwood, 1958; Lewis, 1974; Planquette & Lemasson, 1975) From a quantitative point of view, in Chad, it has been shown the species feeding from sunrise to about 4.00 pm absorb according to the season, between 1.2 and 2.7% of its body weight per day, with a feed gain ratio roughly estimated at 11.0 (Lauzanne, 1969). According to this author (Lauzanne, 1978), the calorific equivalents for a 1 gram sample are for this species:
In as much as they do not contain carbohydrates, the calorific value of fish mainly depends of their fat content. So, in A. baremoze the lipid rate reaches more than 40 per cent (Laure & al., in Lauzanne, 1978). In a comparative capacity, in Lates niloticus that have no more than 10 per cent of lipids, the calorific value is only 5 940 cal/g.
Alestes baremoze: diet in rivers and lakes.
Embryonal development
Durand & Loubens (1971) resorted to fish farming after artificial insemination so as to observe fry development. Ripe ova spawned by the female are 1.0 to 1.4 mm in diameter. In contact with water, they swell to reach 3.2 to 4.1 mm. Although the eggs triple in size, they remain denser than water and do not stick to the substrate on which they are placed. Thus, they are free demersal eggs. The hatching occurs after 17 to 22 hours. A short time after hatching, the nearly straight larvae reach 3.5 mm TL and possess a yolk sac that will be resorbed after 2 weeks. During the first 3 days, larvae only move vertically by body undulations although they are very active. Horizontal swimming only appears on the fourth day. The larva then reaches a mean total length of 5.6 mm. From the 5th to the 12th day, the general aspect is still the same. It is only after this that the development regains a faster rhythm. Apart from pectoral fins that appear following the third day, fins appear as follows : caudal, dorsal and anal fins simultaneously from the 12th to the 23rd day. Then, at the same time, pelvic and adipose fins appear from the 20th to the 30th day. The development of the final part of the backbone extends from the 12th to the 24th day. At one month old, juveniles reach 17.5 mm TL and already look like adults. Nevertheless, a residual primordial fin remains.
Hybridization
Periodically in Kossou dam in Côte d'Ivoire, a form closely related to A. baremoze is found, but it can be distinguished by certain features (Daget & Kouassi, 1978).
Alestes baremoze: difference in meristic characters in Kossou dam between A. baremoze and the supposed hybrid (source: Daget & Kouassi, 1978).
This form is not identified with A. dentex, A. liebrechtsii and A. macrophthalmus, especially because these species was never reported in this region. Such specimens have not been found upstream or downstream of the dam in spite of very intense fishing. Consequently, the only plausible interpretation accepted by the authors is the hybridization of A. baremoze and a species of Brycinus present in the lake too. Among distinctive features already pointed out and as well as the general aspect closely related to A. baremoze, this supposed hybrid possesses a well-developed adipose eyelid. At the back, there is a rudiment of fontanel, thus indicating an intermediate step between Alestes s.s. and some Brycinus.
Hybrid of Alestes baremoze x Brycinus sp. caugh in Kossou dam (Côte d’Ivoire).
Migration
Authors are agree to say that this species migrates anadromously for reproduction every once a year (Daget, 1952; Loubens, 1973; Durand, 1978). Our own observations in Côte d'Ivoire, have allowed us to note an upstream migration of the breeding stock during the rise in the water level. Finally, in the areas where floodplains exist, there are lateral migrations that lead individuals from low water levels towards the periphery flooded during the rise in the water level, then bring them back to low water levels when the water level drops (Daget, 1952).
Distribution
Described from a Nile specimen, found in Lake Albert, this species also occurs in the endorheic system Omo-Lake Turkana. A. baremoze also occurs in Sudan-Sahelian Western Africa in Senegal, Gambia, Niger, Volta and Chad basins.
Finally, it occurs in certain Western African coastal basins such as Tominé River and the following basins in Côte d'Ivoire: Sassandra, Bandama and Comoé. On the other hand, it is not found in Guinean Africa and in the coastal basins of Togo and Benin (see Faunafri).
This species has a wide distribution, with no known major widespread threats. It is therefore listed as Least Concern. It has also been assessed regionally as Least Concern for east, north, and west Africa. This species used to be found along the whole River Nile, including in Delta Lakes, Rashid branch and Lower Nile. It is now restricted to the upper Nile (outside the Northern Africa Region) due to the High Dam (Lake Nasser) construction, as is therefore listed as Regionally Extinct within the north Africa regional assessment.
Major threats: regionally, this species faces different threats:
Bibliography
Alestes dentex (Linnaeus, 1758)
Types and type localities
Cyprinus dentex Linnaeus, 1758: 325-326. Type locality: “Habitat in Nilo”. Holotype NRM 49.
Characinus niloticus Geoffroy Saint-Hilaire, 1809. Type locality: “Nile River”. No type known.
Myletes hasselquistii Cuvier, 1818: 449. Type locality: “Nil (Egypte)”. Syntypes MNHN n° 6301, A.9713-9715.
Alestes sethente Valenciennes in Cuvier & Valenciennes, 1849: 190. Type locality: “Sénégal”, syntypes MNHN A.9716 (5 ex.).
Synonyms
Cyprinus dentex Linnaeus, 1758
Salmo dentex(partim) Linnaeus, 1766
Salmo niloticus Forskål, 1775: 66
Characinus niloticus Geoffroy Saint-Hilaire, 1809
Myletes hasselquistii Cuvier, 1818
Alestes dentex Müller & Troschel, 1845
Alestes hasselquistii Valenciennes in Cuvier & Valenciennes, 1849
Alestes sethente Valenciennes in Cuvier & Valenciennes, 1849
Myletes dentex Eigenmann & Ogle,1907
Alestes dentex dentex Daget, 1954
Alestes dentex sethente Daget, 1954
Common names
Adangme: Tewe (Ghana)
Arabic: Kawara baladi/Kawwara baladi/Rie abu asnan (Sudan)
Dinka, Northeastern: Alerio/Cin (Sudan)
El Molo: Nyele (Kenya)
English: Characin/Silversides (Ghana), Nile robber (Kenya), Pebbly fish
Estonian: Hammas-mölderkala
Ewe: Asenti/Asentiwe/Asotiklapa (Ghana)
Finnish: Hammasalesti
Ga: Tewe (Ghana)
Hausa: Mazari/Shemani (Nigeria)
Ijo: Oza (Nigeria)
Kanuri: Kaya (Nigeria)
Kim: Vaï/Van/Vore (Chad)
Mòoré: Mimbre (Burkina Faso)
Not specified: Delete/Juse/Lelete (Kenya)
Nubian: Girfiga (Sudan)
Nuer: Cien (Sudan)
Nupe: Egbagi (Nigeria)
Shilluk: Kodo (Sudan)
Turkana: Dorobela (Kenya)
Wolof: Sèlinthe (Senegal)
Yoruba: Arefe (Nigeria)
Zande: Basongirino (Sudan)
Description
Diagnosis: 43-51 scales in, 8 ½ (rarely 7½) above, and 3½ below lateral line. Anal fin with three spines and 18-23 soft rays; 18-27 gill rakers on lower limb of first gill arch; 45-48 vertebrae. Dorsal-fin origin well behind level of pelvic-fin insertions, but not as far as in A. baremoze.
Maximum reported size: 410 mm SL (440 g) from the Chad basin. Greenwwod (1956) reports a specimen of 550 mm from Lake Albert, but it is not certain whether he means stadard or total length.
Colour: overall colouring of this species is silvery with a darker dorsum, grey or bluish. Lower sides and belly are white. Fins are greyish or slightly yellow to orange, and only one lower lobe of the caudal fin is red. On the other hand, the posterior margin of the caudal fin is black. There is neither a post opercular mark nor a precaudal blotch.
Affinities: throughout its general appearance, A. dentex is closed to A. baremoze with which it may be confused. However, in comparison with the latter, A. dentex has a heavier body, a dorsal-fin insertion located less far back, an anal fin which is shorter and has less branched rays, but most of all the number of gill rakers on the lower limb of the first gill arch is lower, never exceeding 27, whereas it is at least 30 in A. baremoze. In comparison with other species of Alestes s.s., there is no reason why they should be confused because of the allopatric characteristic of their distribution.
Remarks: two subspecies are generally recognized on the basis of meristic counts:
The 3 syntypes of M. hasselquistii MNHN n° A.9713 and the syntype of A. hasselquistii MNHN n° A.9714 must be related to A. baremoze and not to A. dentex. Different features found on other types of A. dentex are given below.
Alestes dentex: main morphological characters of the types.
Alestes dentex: number of anal fin rays.
Alestes dentex: number of lateral line scales.
Alestes dentex: number of vertebrae.
Populations
In 1849, Valenciennes described A. sethente from the River Senegal which he thought to be related to A. dentex from Nile but different. Other authors noted the difference too (Günther, 1864; Steindachner, 1870; Sauvage, 1880) before Boulenger (1907) put these two species into synonymy. Eventually, comparing his own count of anal fin rays and lateral line scales with Boulenger's (1907) and Steindachner's (1870), Daget (1954) thought there was no reason why we should consider two different species because of body proportions nearly equivalent. On the other hand, it was reasonable to recognize two sub-species of which some meristic features present significantly different variations (see tables above). Now, all authors acknowledge these two sub-species A. dentex dentex from Nile and A. dentex sethente from Sudan river systems of Western Africa.
Growth
It doesn't exist a lot of works on the biology of A. dentex because it is less frequent or less often collected than its sister species, A. baremoze. The only results about growth are those of Daget (1952, 1954 and 1957) obtained in the River Niger (see below) where A. dentex is subjected to a long growth stopping of about six months during the low water period. It can also be pointed out that males’ growth is slower than that of the females.
Alestes dentex: growth (length and weight) for males and females in the Niger river basin MRS: Maximum Reported Size (standard length), MRW: Maximum Reported Weigth.
In Niger River, the maximum tsandard length observed (MSO) is 369 mm SL (450 mm TL) for females and 333 mm SL (420 mm TL) for males. These two specimens weighed 625 and 325g respectively. For other river systems, MTL are:
Reproduction
In Niger River basin, A. dentex reach their sexual maturity at the end of the second year (Daget, 1952 and 1954). The spawning takes place at the end of July or in early August. Then, the spawn would be laid in low water levels. It is only after this that the fry reach the floodplains. In Gambia River (Svensson, 1933), Senegal River (Reizer et al., 1972), Chad basin (Blache et al., 1964) and lake Volta (Petr, 1968), the spawning also occurs during river floods, but generally the authors noted it occurs later than in A. baremoze. On the other hand, in Jebel Aulyia dam (Bishaï, 1977b) (Nile River basin), the spawning period takes place from April to August. Thus, there is no relationship with the rise of the water level that lasts from July to August. According to this author, temperature is the main factor for spawn induction. Nevertheless, in view of the obtained results, we can note that the highest number of mature specimens is found from June to August. Ovaries of A. dentex are grey-green and have a lot of ova as in A. baremoze:
Diameter of the eggs is about 0.7 to 1 mm for the Nile specimens.
Diet
According to results obtained in various river systems, in various biotopes and at different times, it appears that A. dentex feeds on any available food. Nevertheless, we note as a rule that A. dentex has a more pronounced preference to plants and seeds than A. baremoze. In conclusion, results obtained by various authors in various river systems are given below.
Alestes dentex: diet in some different rivers of Africa.
Migration
Apart from classical lateral migrations that lead fish from low water levels towards floodplains during the rise in the water level and vice versa at the beginnings of low water, Daget (1952) notes that there are complex longitudinal migrations in the mid-Niger flow: “A pattern is established early on which remains throughout the low water level period. During low water, it can be observed upstream from Diafarabé, there is a predominance of one-year-old A. dentex and A. baremoze, but downstream from Mopti there are more A. dentex aged two years or more, together with younger fish from both species and older A. baremoze. As soon as the water level rises again, the situation changes. It appears that all of them swim upstream to Markala, then back downstream again, but different age groups of A. dentex and A. baremoze, move at different speeds whilst remaining mixed together so that in any given place a diagram of catch would show the percentage of different age-groups of the two species changes progressively. The results of several tests carried out on different dates at Diafarabé and Markala have led us to this conclusion (…) ”. In the same way, in the Chari delta, A. dentex catches are larger from August to December with a peak in September. Migratory fish are of average size and are sexually inactive. It is probably specimens which come from the lake that will reproduce the following year high enough upstream (at least 250 km) as no mature specimens have ever been found in the lower river system (Loubens, 1973). The migration of A. dentex is far bigger in size than that of A. baremoze and appears to take place at a younger stage in their development.
Distribution
A. dentex was described from the Nile and is known all over the Nile system including Lake Albert and Omo-Lake Turkana system. On the other hand, this species can be found in Sahelo-Sudan river systems of Western Africa: Senegal, Gambia, Niger, Chad and Volta. A. dentex is more strictly Sudan than A. baremoze. No specimens were found either in Côte d'Ivoire, even in the Bagoé River which is a tributary of Niger River, nor in Tominé River , nor in Upper Volta systems (see Faunafri).
This species has a wide distribution, with no known major widespread threats. It is therefore listed as Least Concern. It has also been assessed regionally as Least Concern for east, northeast, and west Africa. Within northern Africa the species is only found in Egyptian Upper Nile (regions Assiut, Sohag and Aswan) and meets the criteria for Vulnerable.
Regionally, this species faces different threats:
Bibliography
Alestes inferus Stiassny, Schelly & Mamonekene, 2009
Type and type locality
Alestes inferus Stiassny, Schelly & Mamonekene, 2009: 110-116. Type locality: “Democratic Republic of Congo, Bas Congo Province, Mpozo River main channel at bridge near confluence with Congo River mainstream, 5°50'5"S, 13°29'42"E”. Holotype: AMNH 242136. Paratypes: AMNH 242137 (4), 242138 (4, 2 c&s)
Common names
Estonian: Kongo mölderkala
Description
Diagnosis: distinguished from all congeners by the possession of fewer pored scales along the lateral line (31–33 versus 36–51) and fewer vertebrae (39–40 versus 41–49). Alestes inferus is further differentiated from A. dentex, A. baremoze, and A. stuhlmanni in the possession of fewer gill rakers along the lower limb of the first arch (15–17 versus 23–58).
Maximum reported size: 94.3 mm SL.
Colour: in alcohol base body coloration yellowish brown dorsally, pale cream ventrally. A darkly pigmented, deep-lying stripe extends from dorsoposterior margin of opercle to base of caudal peduncle, not extending over caudal fin. Trace of a band of dark melanophores present above anal fin. Pectoral and pelvic fins creamy white. Adipose fin dusky gray with a narrow marginal band of darker pigment. Dorsal fin somewhat dusky proximally with yellow-orange band mid-dorsally, dusky gray proximally. Anal fin pale proximally becoming darker along distal margin. Caudal fin dusky gray with yellow-orange patch posteriorly on dorsal and ventral lobes, distal margin dark gray. In life with blue-green iridescence dorsally and dorsolaterally, silvery-white laterally and ventrally. No trace of midlateral band or of melanophores above anal fin. Pectoral and pelvic fins pale yellowish hyaline. Dorsal fin hyaline proximally, orange distally. Adipose pale dusky gray with a narrow darker gray distal margin. Anal fin pale dusky gray. Caudal fin pale dusky gray, orange banding along the posterodorsal and posteroventral lobes, and with a narrow, dark gray distal margin.
Alestes inferus: morphometric characters
Alestes inferus: meristic characters
Distribution
Alestes inferus is currently known only from the type locality in the main channel Mpozo River downstream of the bridge crossing near its confluence with the mainstream Congo River, (5°50'50”S, 13°29'42”E). Specimens were collected with cast nets in shallow water and in deeper pools alongside emergent grasses at the riverbank over a substrate dominated by large rocks and rock rubble (see Faunafri).
IUCN assessment
Not evaluated
Bibliography
Alestes liebrechtsii Boulenger, 1899
Type and type locality
Alestes liebrechtsii Boulenger, 1899: 29. Type locality: “Haut Congo, Upoto, Umangi”, Syntypes MRAC n° 122, 140, 168
Synonym
Alestes liebrechtsi Géry, 1968b
Common names
Estonian: Liebrechtsi mölderkala
Kele: Akela/Bosoto/Ikekela/Lisenge (Democratic Republic of the Congo)
Lombo: Bosoto/Lisenge (Democratic Republic of the Congo)
So: Bosoto (Democratic Republic of the Congo)
Description
Diagnosis: gill rakers are not numerous for this group of species and are also relatively short. There were neither humeral mark nor precaudal blotch on specimens we examined. The first three branched rays of the anal fin are strongly ossified in the largest specimens.
Maximum reported size: 400 mm TL.
Colour: overall coloration is silvery with a darker dorsum and a lighter belly. Above the lateral line, scales are steel blue. According to Matthes (1964a): "Golden to coppery eye, yellow-grey externally, blackened at the upper and lower edges. All the fins are strongly blackened, yellowish ; dorsal and caudal fins are red-tan. The lobes of the caudal fin are often vivid red.". In alcohol, every fins remain grey with however a more pronounced coloration of the pectoral fins.
Affinities: according to its general appearance A. liebrechthsii is related to all the species of genus Alestes s.s. Nevertheless, according to its distribution, it can only be confused with A. macrophthalmus. It can be distinguished from this species thanks to its lower number of branched rays at the anal fin (14-16 versus 17-20).
Alestes liebrechtsii: main morphological characters of types and additional material (* total length).
Reproduction
According to Matthes (1964a), only specimens collected in early April in Lake Tumba and Lake Ikela area were in the process of maturation. Thus, it appears that there is a spawning season corresponding to floodwater.
Diet
A. liebrechtsii is omnivorous. It feeds on plant detritus of all kind, aquatic insect larvae, terrestrial insects fallen into the water and small fishes (Gosse, 1963; Matthes, 1964a). Juveniles have a more microphagous diet and feed on Diatoma, filamentous algae and Cladocera. However, plant and animal detritus can be found in their stomach contents.
Distribution
A. liebrechtsii is an exclusively Congolese species that is just as well encountered in Congo River mainstream than in its tributaries and in lakes belonging to this basin. The species has also been reported from River Malagarazi (Banister & Bailey 1979), Tanzanian tributary of Lake Tanganyika, but it appears there was in this case a misunderstanding with A. macrophthalmus that is encountered in Tanganyika system although A. liebrechtsii has never been reported from there (see also Faunafri).
The species is widespread or without major threats throughout the Central Africa assessment region and is assessed as Least Concern.
Major threats:no information available.
Bibliography
Alestes macrophthalmus Günther, 1867
Types and type localities
Alestes macrophthalmus Günther, 1867: 113. Type locality: “Gabon”, holotype BMNH n° 1867.5.3:25
Alestes ansorgii Boulenger, 1910: 542. Type locality: “Quanza River at Cunga and Dondo and from the Lucalla River at Lucalla”, syntypes BMNH n° 1910.11.28:65-70
Synonyms
Alestes ansorgii Boulenger, 1910
Alestes ansorgei Pellegrin & Roux, 1928
Alestes (Alestiops) macrophthalmus macrophthalmus Hoedeman, 1951
Alestes (Alestiops) macrophthalmus tanganiica Hoedeman, 1951
Common names
Bemba: Manse/Mibanse/Misebele (Zambia)
Chokwe: Lumbase/Lutemba/Muka/Musalusalu/Nganzama/Susulu (Angola)
English: Torpedo robber (Zambia)
Estonian: Heering-mölderkala
Finnish: Sillialesti/Sillitetra
French: Ablette (Gabon)
Hausa: Shemani (Nigeria)
Kanuri: Kaya (Nigeria)
Luba-Kasai: Kusu (Angola)
Not specified: Fabara/Ogoundu (Gabon)/Kapasa (Angola)
Nupe: Egbagi (Nigeria)
Yoruba: Arefe (Nigeria)
Description
Diagnosis: 36-44 scales in, 6½ or 7½ above, and 3½ below lateral line. Anal fin with three spines and 18-20 branched rays; 17-22 gill rakers on lower limb of first gill arch. Dorsal-fin origin at about the same level as pelvic-fin insertions.
Maximum reported size: 600 mm SL (2,000-2,500 g). A. macrophthalmus is the largest species of Alestes s.s. known.
Colour: silvery, back darker, bluish or greenish, lower sides and belly white. Pectoral and pelvic fins sometimes blackish. There are no humeral or precaudal marks. According to Boulenger (1909) "silvery, bluish or greenish dorsum ; pectoral and pelvic fins sometimes blackish".
Affinities: among the Alestes species, A. macrophthalmus have less gill rakers than A. baremoze and A. stuhlmannii (17-22 versus more than 30), the dorsal fin is not located at the back of the pelvic-fin insertion as in A. dentex and, finally, has more anal fin branched rays than A. liebrechtsii (17-20 versus 14-16).
Alestes macrophthalmus: main morphological characters of types and additional material (* total length)
Populations
According to typical populations from Congo and Cameroon, two groups can be distinguished regarding the values some meristic characteristics take. As already seen, fishes from Angola and Kasaï River have less scales along the lateral line. In the same way, A. macrophthalmus tanganiica Hoedeman 1951 has less gill rakers on the lower limb of the first gill arch (13-16 versus 17-20) (Poll, 1953). Nevertheless, all the other features overlap. Thus, we think, according to its wide distribution and the fact that it is found in various basins, that A. macrophthalmus tends towards a speciation in each of them. For the time being, we will only admit the presence of three sub-species:
Reproduction
In Lake Bangweulu, the youngest specimens reach their sexual maturity at about 100-110 mm FL (Bowmaker, 1969). The spawning period is spread enough as we find a good proportion of mature specimens from July to March. Nevertheless, most of them spawn between August and February. In Lake Tanganyika, the spawning period lasts several months too (Poll, 1953). In Lake Bangweulu, A. macrophthalmus stays in the lake to reproduce and places of spawn are located in rocky or sandy areas. This observation is opposite to those noted in other places where the species make an anadromous migration to reproduce. Demersal eggs, once they are laid and fertilized, are left. At maturity, ova reach a diameter of 0.8-1.7 mm. The fecundity is about the one observed in other Alestes and the equation corresponding to the number of eggs being a function of female sizes may be written as follows : f = 142.8 FL-16,353 (with f = number of eggs and FL = fork length in mm).
Growth
The only data concerning the growth of A. macrophthalmus is issued from studies carried out on fishes from Lake Bangweulu (Bowmaker, 1969). Petersen's method used to follow young groups allows to appreciate the growth of those fishes during the first seven months. Thereafter, because of the lack of possibilities to observe bone structure, the author tried to determine a growth curve from structure distributions in size of the collected specimens. Although it does not look like usual growth curve in length, we will note however that the growth of the species follows more or less those of A. baremoze and A. dentex that at the same age reach approximately the same sizes. Finally, we will notice that in Lake Bangweulu, the maximum size recorded is 340 mm FL corresponding to that found for A. baremoze and A. dentex in River Niger. From original data, we worked out the parameters of the growth curve which are respectively, L inf. = 417.5 mm et k (monthly) = 0.018. We can notice that L inf. has a high value and at the contrary, this of k is weak enough. We impute this phenomenon to weak growth of young that appears to be enough underestimated during the first two years. Moreover, for specimens which do not exceed six year old (Bowmaker, 1969), it appears that the part of the curve corresponding to the older specimens does not show reorientation and does not tend towards an asymptotic value. Indeed, and according to the fact that the reproduction season is very spread in time (see below), it appears that the observed modes correspond to age groups of individuals which can be born at different time in the course of the same year. So, the correspondence between size and age may be erroneous.
Alestes macrophthalmus: growth in length in Lake Bangweulu, MRS: Maximum Reported Size (fork length).
Diet
Wether in Lake Tanganyika (Worthington & Ricardo, 1937; Poll, 1953) or in Lake Bangwulu (Ricardo-Bertram, 1943; Bowmaker, 1969), it appears that A. macrophthalmus has an omnivorous diet based on fish, aquatic insects and plants. A complete study of Bowmaker (1969) shows that the diet diversifies according to the size of the specimens which are mostly insectivorous when they are young and become more and more piscivorous as they grow. On the other hand, the author did not note any modification of the feeding regime according to the seasons. The only differences noted are due to a momentary overabundance of a prey group.
Alestes macrophthalmus: diet in Lake Bangweulu.
Distribution
A. macrophthalmus occurs all over the Congolese basin as Lake Tanganyika. It can also be found in coastal river systems of Cameroon and Gabon, and in Quanza River in Angola (see also Faunafri).
This species has a wide distribution, with no known major widespread threats. It is therefore listed as Least Concern. It has also been assessed regionally as Least Concern for central, east and west Africa.
Major threats: little information is reported on threats to this species. In central Africa, it has commercial importance. In eastern Africa it is reportedly threatened by water turbidity and siltation as a consequence of erosion and farming extension on the watersheds.
Bibliography
Alestes stuhlmannii Pfeffer, 1896
Types and type localities
Alestes stuhlmannii Peffer, 1896: 44. Type locality: “Kingani River”, Syntypes ZMHU n° 13675
Alestes adolfi Steindachner, 1916: 64-65. Type locality: “Ulanga-Flusse bei Ifakara” (Tanzania), Syntypes (3) NMW n° 66697-66698(2)
Synonyms
Alestes adolfi Steindachner, 1916
Alestes (Alestiops) stuhlmanni Hoedeman, 1951
Common names
Estonian: Stuhlmanni mölderkala
Swahili: Kasa/Ngacha (Tanzania)
Description
Diagnosis: according to Boulenger (1909), the main difference between A. stuhlmanni and other species of the genus lies in the fact that the teeth number is more important on premaxillary external row (8 versus 6). In fact, we always counted 6 teeth. Thus, through this characteristic, A. stuhlmanni looks like all other Alestes s.s.
Alestes stuhlmannii: main morphological characters of types (* total length)
According to Murray (2004): Alestes stuhlmannii is fusiform with a terminal mouth and a snout that becomes more blunt in larger individuals. All specimens had a well-developed adipose eyelid. The dorsal fin is in the middle of the back, and the adipose fin is closer to the caudal than to the dorsal fin. Of the all specimens examined, one lacked an adipose fin. As in other characiforms, the pectoral fins insert at or just behind the posterior extent of the head and low on the body. The insertion of the pelvic fin is slightly anteriorly to the dorsal fin origin. The anal fin base is much longer than the dorsal fin base, and the caudal fin is forked. The body is covered with large cycloid scales which extend onto the bases of the anal and caudal fins. There are no scales on the head and none on the supraoccipital crest. The lateral line scales start just behind the opercular bone, and, after about the third scale, the lateral line drops down two scale rows, then remains low on the body. The last few (one to three) pored scales are on the caudal fin (see measurements and counts in tables below).
Alestes stuhlmannii: measurements and ratios based on 142 specimens from the Rufiji River system (from Murray, 2004).
Alestes stuhlmannii: meristics for specimens from the Rufiji River system (from Murray, 2004).
Maximum reported size: 210 mm SL.
Colour: according to Murray (2004) “although all examined specimens had the same history of preservation, larger alcohol-preserved specimens were yellow, while smaller ones were light brown. The flanks of all specimens were darker dorsally than ventrally. A thin, dark line ran along the flank from the posterior edge of the opercle to the base of the caudal fin rays; it did not follow the lateral line and was not confined to a single scale row. The inside edge of the caudal fin fork was darker than the rest of the fin. The adipose fin in alcohol-preserved specimens was usually dark with a light distal edge, although in some it was light with a dark distal edge”.
Affinities: as well as its particular distribution, A. stuhlmannii differs from other Alestes s.s. in the very high number of gill rakers present on the lower limb of the first gill arch (45 to 60 versus 41 at the most). Howerver, we have to admit that the number of gill rakers increases with growth in A. stuhlmannii, from 15 in the smallest specimen to 58–61 gill rakers on the lower limb of the first arch in specimens >175mm LS (Murray, 2004) (see figure below).
Alestes stuhlmannii: number of gill rakers in relationship to standard length (redrawn from Murray, 2004).
Alestes stuhlmannii: upper and lower jaw teeth.
Distribution
A. stuhlmannii is present in the coastal basins of Tanzania: Kingani, Wami, Rufiji, Ruvu and Kilombero Rivers (see also Faunafri).
This species is widespread in major river basins in Tanzania with no major threats identified. It is therefore assessed as Least Concern.
Major threats: no information available.
Bibliography
