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Vundu: heterobranchus longifilis valenciennes, 1840.

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Description

Dorsal fin 31-39; anal fin 46-50; head large, 3-4 times into SL. Diagnostic features: large, prominent adipose fin, short rayed dorsal fin and very long barbels.

Heterobranchus longifilis can be distinguished from all other Zimbabwean clariids by having two distinct dorsal fins: a short, rayed dorsal fin and a long adipose fin. The rayed dorsal fin has no more than 40 rays compared to at least 50 in the other species. The adipose fin extends from the posterior end of the rayed dorsal fin to the caudal fin. The species also has very long barbels, the maxillary barbels extending almost to the origin of the pelvic fins. Adults are usually olive grey to reddish brown in colour, darkest on the dorsal surface becoming paler on the flanks, with an off-white belly. Juveniles have irregular black spots, a black tip to the adipose fin and a black band towards the end of the caudal fin. This is the largest Zimbabwean fish species and grows to about 1.2m in length and 55kg in weight. Claims of much larger specimens remain unverified and are probably exaggerated.

Distribution

The vundu occurs throughout much of Africa, and is found in the Senegal, Niger and Nile systems, and south to the Congo and middle and lower Zambezi. In Zimbabwe, vundu occur only in the Zambezi below Victoria Falls and are largely confined to the main stream of the Zambezi River and, to a lesser extent, the valley sections of the larger tributaries. Specimens have occasionally been taken from the plateau sections of these rivers (Bell-Cross and Minshull, 1988), and there is a record of a 34kg (84lb) fish taken from the Manyame River at Chinhoyi in 1955 (Salt, 1978), while a 31.6kg (69.5lb) specimen was taken from the Mazowe River in 1954 (Anon, 2003a). Vundu are probably no longer found on the plateau in any numbers now, owing to the changes that have taken place in the rivers over the last fifty years.

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Biology

Abundance: Heterobranchus longifilis is not a particularly abundant species, and in Lake Kariba it accounted for only a small percentage of the inshore fish biomass. Only 98 (0.1%) out of a total of 134 565 fish, were caught in an experimental gill-netting program between 1969 and 1992 (Karenge & Kolding, 1995a). By contrast, 3 620 sharp-toothed catfish (Clarias gariepinus) (or 2.7% of the total) were caught during the same period. No vundu were captured in a survey carried out at Mana Pools in 1971-1972 (Kenmuir, 1976), but this probably reflects the fact the survey was done in flooded pools and inlets, where the vundu is unlikely to occur. It seems, in fact, to be most common in deep pools in the main stream of the river and may be especially abundant in the deep stilling pool below the Kariba Dam.

Feeding

Like other clariids, the species is omnivorous and will eat any kind of food that is available. Juveniles feed on aquatic insects such as dragonfly and mayfly nymphs, and the larvae and pupae of midges, but larger specimens are primarily carnivorous. They feed on all kinds of fish and other animals, and will scavenge offal if it is available. One specimen was found with a small beer bottle in its stomach, and another with kudu hooves (Kenmuir, 1983), while one fish captured below the dam wall weighed 42kg and had a 5kg tigerfish in its stomach (this fish is illustrated in Kenmuir, 1983). Thirteen stomachs examined by Mitchell (1976) were found to contain plant material (including maize-meal porridge, "sadza"), crustacea, mayfly and dragonfly nymphs, termites, dipteran larvae and pupae, terrestrial insects, a reptile eggshell and fish. Fish were the most important item and included Barbus unitaeniatus and Pharyngochromis acuticeps. A 15.9kg (35lb) specimen caught in the Sanyati River near its confluence with the Zambezi, in pre-Kariba days (1955), had an 82cm (32inch) crocodile in its stomach (Anon 2003b).

Breeding

Little is known about the breeding biology of vundu, but, unlike Clarias, probably do not migrate into flowing streams to spawn. Large individuals have been seen in the stilling pool below the Kariba Dam surrounded by a "milky cloud" which may have been milt and eggs, suggesting that they were spawning there (unpublished observations). Minshull collected 2cm fingerlings in flooded terrestrial grass in April at the Olive Beadle camp at the head of Lake Kariba.

Growth and mortality

Fish from Lake Kariba were estimated to grow to about 65cm in length and 4kg in weight in 10 years (Frank, 1974). This is almost certainly an underestimate because it means that the record fish of around 40kg would have to be about 100 years old, which seems unlikely. Under experimental conditions, vundu grew to 700g in 224 days (about seven months), which is more than four times faster than the rate given in Frank (1974). Its growth rate was about twice that of Clarias gariepinus reared under the same conditions (Legendre et al., 1992).

Angling and economic importance

The vundu is a popular angling fish and can fight powerfully, especially if assisted by a strong current in the river. It requires heavier tackle than other species, and common baits include meat and offal (liver, hearts, kidneys), plucked birds and fish, while smaller ones will take a spoon. Old-fashioned "blue" soap was said to be an effective bait, but the efficacy of modern soaps is unknown. Many visitors to Lake Kariba set long-lines at night in the hope of catching a vundu; these frequently break and there must be a number of these fish in the lake with fishing tackle in their mouths.

Conservation

The population biology of vundu is largely unknown and the effect of removing large individuals has not been determined. In general, large fish are vulnerable to fishing pressure if they take long to reach sexual maturity and juvenile mortality is high. The situation of the vundu needs to be monitored carefully. Recent moves by angling organisations (e.g. Bassmasters, Bulawayo and Harare Light Tackle Clubs) to encourage catch and return angling for vundu suggest that anglers are becoming concerned about this species and their efforts should be encouraged. Roger Bills noted that three weeks of fishing in Lake Cahora Bassa in 2008, using varied appropriate methods, indicated that this species is in trouble there.
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Title Annotation:Species Fact File
Author:Marshall, Brian
Publication:African Fisherman
Date:Aug 1, 2016
Words:1054
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