Hydrocynus
The species of the genus Hydrocynus (dog- or tigerfishes) are strictly ichthyophagous, well- known for their liveliness and voracity. All of them are rather similar in appearance, their distinction requiring careful examination. Body shape elongate, well-suited for their active feeding habits, since they pursue their prey. General colour pattern brilliant silvery, each scale marked by a dark spot, this resulting in a pattern of parallel bands particularly well visible above lateral line, the darkness of these lines varying with species. Following species, dorsal fin beginning at, or before, level of pelvic-fin insertions. Both jaws armed with a single row of strongly developed, cutting teeth (9-14/8-12) ; eye almost entirely covered by an adipose eyelid.
Synonyms
Hydrocynus Cuvier, 1817 (partim)
Hydrocyon Cuvier, 1819
Hydrocionichthys Travassos, 1952
Type species
Salmo dentex Geoffroy Saint-Hilaire, 1809 [= Hydrocyon forskahlii (Cuvier, 1819)] by subsequent designation of Agassiz, 1829.
For most authors, five species are assigned to the genus Hydrocynus, but we consider that H. tanzaniae is a questionable species (see below).
Key to species.
1 3 scales rows between lateral line and the scaly process located at pelvic fin base............................................H. brevis
2 scales rows between lateral line and the scaly process located at pelvic fin base........................................................2
2 Rayed dorsal fin origin in front of pelvic fin insertion; dorsal adipose fin grey....................................................H. forskalii
Rayed dorsal fin origin at about the same level (or slightly behind) as pelvic fin insertion; dorsal adipose fin black.............3
3 Gill rakers very short, less than one third the length of the gill filaments; lateral line with 53-58 pored scales.......H. goliath
More than 35 scales along the lateral line....................................................................................................H. vittatus *
* The synonymy of H. vittatus with H. forskalii proposed by Brewster (1986) does not appear well founded (Paugy & Guégan 1989). In her review of the genus Hydrocynus, Brewster never makes the comparison between H. vittatus and H. tanzaniae. For this last species all measurements and counts are similar to those H. vittatus. As no complete study was carried out, we can’t consider H. tanzaniae as synonym of H. vittatus but we think here that H. tanzaniae is a questionable species.
Bibliography
Hydrocynus brevis (Günther, 1864)
Types and type localities
Hydrocyon brevis Günther, 1864: 351. Type locality: “Khartum”. Syntypes BMNH n° 1862.6.17:94-96.
Hydrocyon somonorum Daget, 1954:116-117, fig. 34. Types are no longer extant (Brewster, 1986).
Synonyms
Hydrocyon forskalii (partim) Cuvier & Valenciennes, 1849
Hydrocyon brevis Günther, 1864
Hydrocion brevis Chabanaud, 1934
Hydrocyon somonorum Daget, 1954
Hydrocynus brevis Daget, 1969: 1115
Hydrocynus somonorum Géry, 1977
Common names
Arabic: Kalb el bahr/Kas/Kass (Sudan)
Creole, English: Dog fish (Cameroon)
Dinka, Northeastern: Joklek/Nyanglec (Sudan)
English: Tiger fish (Cameroon, Ghana), Tiger-fish (Sudan)
Estonian: Saheli vesihunt
Ewe: Tsinu vowo (Ghana)
Finnish: Soukkatiikeritetra
Ga: Akao (Ghana)
Hausa: Zawai (Nigeria)
Igbo: Owulueze (Nigeria)
Jula: Wulujigɛ (Burkina Faso)
Kim: Hidi/Hidi Dongahal/Hidi Mandol/Hiding Donbow/Hiding Madara/Hiring (Chad)
Krio: Bathain/Njengbei/T-gbaren (Sierra Leone)
Limba, west-central: Bathain, Rek-rek-ma (Sierra Leone)
Mende: Jumboi, Njengbei (Sierra Leone)
Mòoré: Basoaka (Burkina Faso)
Nubian: Ascela (Sudan)
Nuer: Jioklec (Sudan)
Nupe: Saganci (Nigeria)
Shilluk: Kyeth (Sudan)
Themne: T-gbaren/Ta poff (Sierra Leone)
Wolof: Guer (Senegal)
Yoruba: Ijakere (Nigeria)
Zande: Ngania (Sudan)
Description
Diagnosis: three rows of scales between lateral line and the scaly process located at pelvic-fin bases; 47-55 scales in, and 7½ (rarely 8½) above lateral line. Body rather massive, especially in front. Dorsal fin origin at the same level as, or slightly ahead of, pelvic fin-insertions. Eye small, its diameter less than 60% of interorbital space. Gill rakers rather few (2-3/7-10) and very short.
Maximum reported size: 860 mm SL (8,250 g).
Colour: body brilliant silvery, black lines on back much less distinct than in other Hydrocynus species (e.g. H. forskalii). Fins grey, but some of them, e.g. lower caudal fin lobe and anterior area of anal fin, tinged with reddish-orange; adipose fin black or grey, depending on individuals.
Affinities: this species is distinguished from its African congeneres by its relatively small eye (less than 60% of interorbital space), its very short gill rakers, and the presence of three (instead of two) scale rows between lateral line and the scaly process located at pelvic-fin bases.
Remarks: according to Brewster (1986), H. somonorum Daget, 1954 is a synonym of H. brevis. Daget himself has suggested that this form might not be a valid species, but a hybrid derived from H. brevis and H. forskalii (Paugy & Guégan, 1989).
Diet
Hydrocynus brevis is very hydrodynamic species which has a very high swimming speed. It is a tireless pursuer which gives little chance to its preys. His jaw is armed with formidable teeth enabling it to cut a fish in two with a single blow of mouth. It would be also able to tackle big fish and take a piece as it was showed by Lewis (1974) in Lake Kainji.
In Lake Chad Archipelago (Lauzanne, 1976), H. brevis has a fairly similar diet to that of Lates niloticus (see table and figure below). It consumes mainly: Sarotherodon galilaeus, Alestes dentex and A. baremoze, Labeo senegalensis and Brachysynodontis batensoda. H. brevis also catches, in lesser number, Schilbe niloticus and Petrocephalus bane. From a quantitative point of view, H. brevis mainly feeds on Brachysynodontis batensoda (% V flood: 38.9; % V low water: 50.4).
Hydrocynus brevis: diet in the Lake Chad archipelago (% C: occurrence percentage; (% V:.volumetric percentage; F.I.: feeding index) (from Lauzanne, 1976).
Hydrocynus brevis: diet in the Lake Chad archipelago. The percentage of occurrence is put on the upper radius of the sector and the volumetric percentage on the lower one. The area of parallelogram is proportional to the food index (redrawn from Lauzanne, 1976).
In Lake Chad open waters (Lauzanne, 1976), H. brevis feeds mainly on Schilbe niloticus and Brachysynodontis batensoda. Secondary preys are constituted by Pollimyrus isidori during the low water and by young of Alestes/Brycinus, Labeo and Distichodus during the flood.
All various authors who have studied the diet of this predator conclude that this species is an exclusive ichthyophagous. In Kainji Lake, (Lewis, 1974) diet of H. brevis consists mainly of Alestes, Chrysicthys and Tilapia s.l., but also various other species. This extremely voracious species is capable of taking out pieces of flesh on very large fish, including Citharinus, and also attacking aquatic birds such as Phalacrocorax (cormorant) in nesting areas. In the Niger River (Dansoko, 1975) diet is mainly constituted by Tilapia s.l., Alestes and Synodontis as it was also observed in Lake Chad (Lauzanne, 1976).
Distribution
This species is found only in the Sahelo-Sudanese River basins: Nile, Chad, Niger/Benue, Volta, Senegal and Gambia (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 north eastern and western Africa. It used to be caught from Lower Egyptian Nile to Luxor, now restricted to Lake Nasser, where it is rare, which is outside the northern Africa region, and has therefore been assessed as Regionally Extinct.
Majot threats: one potential threat to this commercial harvested food fish is overfishing, as well as deforestation and pollution (mining and oil industry). In northern Africa, dams, water pollution (agriculture, domestic and commercial/industrial), groundwater extraction and drought pose possible threats.
Bibliography
Hydrocynus forskalii (Günther, 1864)
Type and type locality
Hydrocyon forskalii Cuvier, 1819: 354. Type locality: “Nile”. Syntypes MNHN n° 1691, A.9705-9707-9707-9708.
Synonyms
Salmo dentex (non Hasselquist) Forskål, 1775
Characinus dentex Geoffroy-Saint-Hilaire, 1809
Hydrocyon dentex Rüppel, 1829
Hydrocyon forskalii Cuvier, 1819
Hydrocyon forskali Pellegrin, 1904
Hydrocynus forskalii Fowler, 1919
Hydrocynus forskahlii Myers, 1950
Hydrocynus forskali Johnels, 1954
Common names
Adangme: Akao/Akawo (Ghana)
Alur: Ngasia (Uganda)
Bambara: Baala (Mali, Senegal)
El Molo: Koris (Kenya)
English: Elongate tigerfish (Kenya, Global), Tiger fish (Ghana), Tigerfish (Zimbabwe)
Estonian: Sale vesihunt
Ewe: Asentiwoe-vuwo (Ghana)
Finnish: Tiikeritetra
Fulfulde, Pulaar: Seendu (Senegal)
Ga: Akao (Ghana)
Gungu: Ngassa (Uganda)
Guro: Zubè (Cote d'Ivoire)
Hausa: Danriri zawai/Tsage/Tsege/Zawai (Nigeria)
Igbo: Owulueze (Nigeria)
Ijo: Kabi (Nigeria)
Jula: Wulujigɛ (Burkina Faso)
Kanuri: Kiri shelia (Nigeria)
Kim: Hidi/Hidi Gurlua/Hiding Azolo/Hiring (Chad)
Krio: Ka-gbith/Magborgboi/Sumuneh (Sierra Leone)
Limba, west-central: Kywanka (Sierra Leone)
Mende: Magborgboi (Sierra Leone)
Mòoré: Basoaka (Burkina Faso)
Nupe: Ebma tsagi (Nigeria)
Nyoro: Ngassa (Uganda)
Soninké: Anjoobe/Anjoobin-sance/Sance (Senegal)
Themne: Ka-gbith (Sierra Leone)
Turkana: Lokel (Kenya)
Wolof: Guer (Senegal)
Yoruba: Ijakere (Nigeria)
Description
Diagnosis: two scale rows between lateral line and the scaly process at bases of pelvic fins; 47-54 scales in, and 7½ (rarely 8½) above lateral line. General body shape elongate. Dorsal fin origin placed distinctly before level of pelvic fin insertions. Eye diameter at least 70% of interorbital space. Gill rakers few (3-6/8-10) and rather long.
Maximum reported size: 780 mm SL (6,900 g).
Colour: body with distinct longitudinal dark lines following scale rows. Anterior part of anal fin and lower caudal-fin lobe bright red, the other fins uniformly grey.
Affinities: H. forskalii has only two scale rows between lateral line and the scaly process at bases of pelvic fins (against three in H. brevis). For comparisons with H. vittatus, see information on that species.
Remarks: Brewster's proposal (Brewster, 1986) to synonymize H. vittatus and H. forskalii does not seem justified, in view of the obvious differences between these two forms.
Ecology
H. forskalii is a pelagic, potamodromous species that forms shoals. It is an open water predator often found near the water surface (Bell-Cross & Minshull 1988) and feeds on fishes, preferring long bodied fish as they are easier to swallow and also takes insects, shrimps, grass and snails (Bell-Cross & Minshull 1988). This species is cannibalistic. It is preyed upon by fish eagle Haliaeetus vocifer (Bell-Cross & Minshull 1988). Breeding migrations have been reported up several tributaries of Lake Kariba during the rains (Bell-Cross & Minshull 1988). Spawning takes place most of the year.
In Lake Chad (Lauzanne, 1975; Lauzanne, 1976; Lauzanne, 1983), there is a pronounced influence of the hydrological seasons upon diet of top predators, particularly H. forskalii.
Hydrocynus forskalii: diet in Lake Chad archipelago; diet composition (left) and fishes proportion (right). The percentage of occurrence is put on the upper radius of the sector and the volumetric percentage on the lower one. The area of parallelogram is proportional to the food index (redrawn from Lauzanne, 1976).
Very young specimens feed on zooplankton (Copepoda and Cladocera). When larger than 300 mm, the adults feed on fiahes.
Distribution
H. forskalii has a wider distribution area than other Hydrocynus species since it occurs in both, the savannah as well as the forested areas. In West Africa it is found in the basins of the Chad, Niger/Benue, Ogun, Ouémé, Mono, Volta, Comoé, Bandama, Sassandra, Cess, St. Paul, Mano, Little Scarcies, Gambia, and Senegal. Elsewhere, it occurs in the Nile, Omo and Congo (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, eastern, northern, north eastern and western Africa.
Major threats: bad agricultural practices in areas around the Volta may pose potential threats to this fish species. Increased sediments and levels of pesticides, fertilizers and other agrochemicals can harmfully impact the ecosystems, and negatively affect the fish. Other potential problems include aquatic weeds and pollution from inadequately treated human waste. It is a commercially important fish species with heavy fishing pressure. In northern Africa, dams, water pollution (agriculture, domestic and commercial/industrial), groundwater extraction and drought pose possible threats.
Bibliography
Hydrocynus goliath (Boulenger, 1898)
Types and type localities
Hydrocyon goliath Boulenger, 1898: 23-24, plate XI. Type locality: “Manyanga, New Antwerp”. Syntypes MRAC n° 77 & 166.
Hydrocyon vittatus (non Castelnau, 1861) Boulenger, 1898: 24-25, plate X, fig. 2. Type locality: “Manyanga, Umangi, Upoto”. Syntypes MRAC n° 149 & 165 (this latter name has precedence because Hydrocynus vittatus Boulenger 1898 was invalid as it was preoupied by H. vittatus Castelnau 1861).
Synonyms
Hydrocyon goliath Boulenger, 1898
Hydrocyon vittiger Boulenger, 1907 (as a footnote p.106)
Hydrocynus goliath Poll, 1976
Hydrocynus vittiger Géry, 1977
Common names
Bemba: Manda/Mcheni (Zambia)
Danish: Stor tigerfisk (Denmark)
English: Giant tigerfish (USA)
Estonian: Suur vesihunt
Finnish: Jättitiikeritetra
German: Wasserhund/Wolfsalmler
Kele: Ifwe/Ilembu/Imemenga/Isenekwa/Menga/Soowa (Democratic Republic of Congo)
Lombo: Menga (Democratic Republic of Congo)
So: Menga (Democratic Republic of Congo)
Description
Diagnosis: the elongated body is more or less heavy in the predorsal region. The first medium-sized dorsal fin is located at vertical through pelvic fin insertion or slightly in front of it. The second one, vestigial and rounded, is located at vertical through the posterior tip of the fixed edge of the anal fin. The caudal fin is very curved and its lobes are very elongated. Contrary to other Hydrocynus of which the number of branched rays of the anal fin is 12, this species has 14 branched rays at this fin. The mouth has from 12 to 20 teeth at the upper jaw, of which from 2 to 8 small ones at the posterior edge, and from 8 to 14 teeth at the lower jaw; teeth point just through the skin. Gill rakers, located on the lower limb of the first gill arch, are short and few (8-9). Scales are regularly distributed all over the body, but their number is higher along the lateral line: from 53 to 58 vs 43 to 55 in other species. There are two rows of scales placed between the lateral line and scaly organ of the pelvic fins.
Maximum reported size: 1,330 mm SL (50,000 g).
Colour: overall coloration is silvery, lighter ventrally. Posterior edges of caudal and adipose fins are black.
Affinities: scales are regularly distributed all over the body, but their number is higher along the lateral line: from 53 to 58 vs 43 to 55 in other species.
Distribution
This species is confined to the Ubangi and Lualaba rivers, Lake Upemba, Lake Tanganyika, Central and Upper Congo basin. It is known from throughout the Congo River basin, with exception of the Mweru-Luapula-Bangweulu system (see also Faunafri).
The species is widespread or without major threats throughout central Africa and is assessed as Least Concern.
Major threats: none known.
Bibliography
Hydrocynus tanzaniae Brewster, 1986
Type and type locality
Hydrocynus tanzaniae Brewster, 1986: 199-201, fig. 31-32. Type locality: “Lower Ruvu River, Tanzania” Holotype BMNH 1976.10.21:130, and “Rufiji River, Tanzania” Paratypes BMNH 1981.7.7:41-42, and 1è other specimens
Common names
English: Tanzanian tigerfish (Tanzania)
Estonian: Tansaania vesihunt
Description
Diagnosis: Depth of body 20.0-26.6 (mean = 23.8) per cent of standard length; length of head 18.3-22.2 (mean = 20.4) per cent. The dorsal profile of the head is straight. Interorbital width 6.5-8.1 (mean = 7.3) per cent; 4th infraorbital width 6.0-7.6 (mean = 6.3) per cent; snout length 7.1-9.0 (mean = 8.0) per cent; depth of premaxilla 2.2-3.4 (mean = 2.7) per cent of standard length. Gill rakers short, approximately one-third the length of the gill filaments; 8-9 (mode 9) rakers on the first ceratobranchial. Scales: lateral line with 43-47 scales, 43 (f. 2), 44 (f. 1), 45 (f. 7), 46 (f. 5) or 47 (f. 5). Fins: dorsal with 2 soft, unbranched rays and 8 branched rays in all specimens examined; anal fin with 3 soft, unbranched rays and 12 (f. 16), or 13 (f. 4) branched rays. Teeth similar to those in H. forskalii, with 13 (f. 1), 14 (f. 7), 15 (f. 1) or 16 (f. 1 1) in the upper jaw and 10 (f. 1) or 12 (f. 19) in the lower jaw. Vertebrae: 46-47; counted as abdominal +caudal elements: 28 + 18 (f. 1), 28 + 19 (f. 1) or 29 + 17 (f.2).
Maximum reported size: 247 mm SL.
Affinities: the lateral stripes of H. tanzaniae are distinct and it differs from all other Hydrocynus species in the presence of elongated 3rd and 4th dorsal and anal fin rays. It is distinguished from H. forskalii and H. brevis by the presence of at least 14 upper and 12 lower jaw teeth and a lateral line scale count of 43-47 scales as compared with 46-55 scales in the other two species. The body is deeper (mean = 23.8 per cent of standard length) than that of H. forskalii (mean = 22.6 per cent of standard length) but does not quite approach the body depth of H. brevis (mean = 24.4 per cent of standard length). H. tanzaniae has 3 soft, 12-13 (mode 12) branched anal fin rays compared with 3 soft, 12-16 (mode 14) in H. goliath.
Distribution
The eastward flowing rivers of Tanzania, in the Wami Ruaha and Rufiji river systems (see also Faunafri).
Although only found in Tanzania, this species occurs in several major river systems where it is widespread with no major widespread threats identified. It is therefore assessed as Least Concern.
Major threats: no information available.
Bibliography
Hydrocynus vittatus (Castelnau, 1861)
Types and type localities
Hydrocinus vittatus Castelnau, 1861: 65. Type locality: “lac Ngami”. Neotype: SAIAB [formerly RUSI] 22228.
Hydrocyon lineatus Bleeker, 1863: 125. Type locality: “Côte de Guinée”, Type RMNH n° 3249.
Synonyms
Hydrocyon forskalii (non Cuvier ) Steindachner, 1894
Hydrocyon forskalii (partim) Peters, 1868
Hydrocinus vittatus Castelnau, 1861
Hydrocyon lineatus Bleeker, 1863
Hydrocyon vittatus Boulenger, 1898
Hydrocion lineatus Pellegrin, 1900
Hydrocynus vittatus Fowler, 1936
Common names
Afrikaans: Ngweshi/Tiervis (Namibia), Tiervis (South Africa)
Arabic: Kalb el bahr/Kas/Kass (Sudan)
Bemba: Manda/Nsanga (Zambia)
Chokwe: Kasangi/Muka (Angola)
Danish: Almindelig tigerfisk
El Molo: Koris (Kenya)
English: Ndweshi (USA), Tiger fish (Ghana, Global, Kenya, Namibia, South Africa, Tanzania), Tigerfish (USA, Zambia)
Estonian: Harilik vesihunt
Ewe: Avuwo kordzeasa (Ghana)
Finnish: Linjatiikeritetra
Ga: Akao (Ghana)
German: Gestreifter Wasserhund/Tigersalmler
Hausa: Zawai (Nigeria)
Igbo: Owulueze (Nigeria)
Ijo: Kabi (Nigeria)
Kanuri: Kiri shelia (Nigeria)
Kele: Bongela/Bosenekele/Munda (Democratic Republic of Congo)
Kim: Hidi/Hidi Dare/Hiding/Hiring (Chad)
Lombo: Munda (Democratic Republic of Congo)
Luba-Kasai: Musonga (Angola)
Lwena: Kasanji (Angola)
Nupe: Ebma tsagi (Nigeria)
Nyanja: Mcheni (Malawi)
Nyoro: Wagassa (Uganda)
Sena: Ncheni (Mozambique)
So: Munda (Democratic Republic of Congo)
Swahili: Kachinga (Tanzania)
Turkana: Lokel (Kenya)
Yoruba: Ijakere (Nigeria)
Zande: Ngania (Sudan)
Description
Diagnosis: two scale rows between lateral line and the scaly process located at pelvic fin bases; 43-53 scales in, and 7½ (rarely 8½) above lateral line. General body shape less elongate than that of H. forskalii. Dorsal fin origin at same level as, or slightly before, pelvic fin insertions. Eye diameter at least 70% of interorbital space. Gill rakers few (5-9/9-12), but rather long.
Maximum reported size: 1,050 mm FL (28,000 g).
Colour: ground colour similar to that of H. forskalii, but in H. vittatus, tips of dorsal and adipose fins black, and fork of caudal fin black-edged; the dark coloration may also extend unto the median caudal rays, forming a crescent-shaped blotch.
Affinities: this species is closely related to H. forskalii, but has certain black markings (at tip of adipose dorsal fin and fork of caudal fin) that are lacking in that species. Furthermore, the rayed dorsal fin is not positioned as far forwards as in H. forskalii (Paugy & Guégan, 1989).
Remarks: the synonymy of H. vittatus with H. forskalii proposed by Brewster (1986) does not appear well founded (Paugy & Guégan, 1989) (see figure below).
Compared morphology of Hydrocynus forskalii (top) and H. vittatus (down), sympafric species from the Niger river.
Habitat and ecology
Hydrocynus vittatus is a demersal, potamodromous species. It prefers warm, well-oxygenated water, mainly larger rivers and lakes. All but the largest form roving schools of like-sized fish; aptly described as fierce and voracious. H. vittatus feeds on whatever prey is most abundant but Brycinus, Micralestes, Barbus, and Limnothrissa are favoured (Skelton 2001). It is a useful food fish in some areas (Eccles 1992). Breeding takes pace on a very few days each year, when the first good rains have swollen rivers and streams, usually in December and January at which time it undertakes a spawning migration up rivers and into small streams (Jackson 1961c). The females spawn a great number of eggs in very shallow water, among the stems of grasses and other submerged and partly submerged vegetation and here the young live until the falling of the flood water forces them out of this refuge (Jackson 1961c).
Distribution
Chad basin, Niger/Benue, Ouémé (not verified), Senegal, Nile, Omo, Congo, Lufira, Luapula, Lualaba, Zambezi, Limpopo, Rovuma, Shire, Rufiji and Ruaha rivers, Lake Bagweulu, Lake Mweru, Lake Tanganyika, Lake Upemba and Lake Rukwa (see also Faunafri).
This species has a wide distribution. Although it is locally depleted by heavy fishing pressure, it is generally common and abundant, and is therefore listed as Least Concern. It has also been assessed regionally as Least Concern for central, eastern, north eastern, southern and western Africa.
Major threats: tigerfish have declined in some rivers in southern Africa due to pollution, water abstraction and obstructions such as dams and weirs that prevent passage. Unregulated gillnet fisheries locally threaten the species. East African populations are threatened by heavy fishing pressure, silt loading due to agricultural activities/ deforestation, and pollution due to pesticides for agricultural use. Threats from other regions are not known.
Bibliography
