Because of the harsh aquatic environment, i.e. unpredictable erratic flows, droughts and episodic floods, the ORS (Orange River System) as a whole is relatively poor in indigenous freshwater fish species diversity. The fishes of the ORS have, over long periods of natural selection, adapted to a riverine environment and are mainly bottom feeders or predators. Because of these adaptations, they can benefit from the natural seasonal changes in environmental factors such as flow, temperature and turbidity. They generally spawn from the onset of spring through to autumn, when the river is in its annual high flow period, utilizing the flooded river banks and floodplains, conditions conducive to growth and survival of the young.
Presently, eight fish families are represented by 22 species in the ORS. Of these, three families, represented by five species are alien to Southern Africa, one species of an indigenous family is also alien and one species, indigenous to the subregion, of another family had been introduced to the ORS. The ORS thus only contains 15 indigenous freshwater fish species, representing five families – compare with KwaZulu-Natal’s ±85 species. Of the 15 indigenous fish species, six are endemic to the ORS with four of them Red Data listed. Of the remaining nine indigenous species, two are becoming threatened within the system, while the possibility exists that one could be an endemic subspecies. Freshwater fish species found between Augrabies Falls and the Orange River Mouth as below:
It is endemic to, and widely distributed in the ORS, except for its absence from the Lesotho catchment. It is, however, not abundant in the regulated Orange River between Vanderkloof Dam and the Orange River Mouth. It is a predator and thus essentially a visual feeder which prefers clear, fast-flowing water with a sandy to gravel substrate. It takes approximately seven years to mature sexually, reaching sexual maturity at extreme minimum lengths of 35 (male) and 36 cm (female) and breeds in and below rapids during the first post-winter floods from early spring to summer. Under regulated conditions, temperature probably became its determinant breeding factor with low temperatures (hypolimnetic water) retarding breeding, initial growth rates and juvenile survival. Although predators generally occur at lower densities than prey species, this species’ extremely low numbers in the regulated Orange River to river regulation and increasing catchment utilization adversely affecting its reproduction, recruitment and dependence on visibility for feeding, and suggests that it is Red Data listed.
It has a natural distribution from the ORS northwards to the Kunene, Limpopo and Zambezi River Systems, and, from the Limpopo southwards, to the Tugela River in KwaZulu-Natal. It is widespread, but not abundant, in the lower Orange River. It is an omnivore, feeding on aquatic vegetation, zooplankton, small crustaceans, insect larvae, nymphs and worms. It prefers well vegetated, silted shores, pools and backwaters in slow flowing riverine areas. It is a substrate spawner, with monogamous habits, which breeds from spring to late autumn. Spawning and fertilization takes place in a hollow, and eggs and fry are guarded by both adults. Occasionally, eggs and fry are picked up in the mouth to be moved to other sites, but no mouth brooding occurs. This species seems to benefit from river regulation and catchment utilisation as river regulation and catchment utilisation stimulate the development of Phragmites reed beds, which, in turn provide shelter and enhance flow stabilisation and silt deposition, thus creating habitat for this fish species.
It is endemic to Orange River System and widely distributed in the ORS in both warm and cold waters, but is, however, not common, even in its preferred habitat and is therefore Red Data. It is an omnivore, feeding primarily on aquatic insects, larvae and nymphs, with large specimens taking small fish. Predation (visual feeding) thus also forms a major part of its feeding habits. It appears to be highly specialised regarding its habitat requirements, consisting basically of a rock/sand/gravel substrate and ranging from bedrock with/without scattered rocks and sandy to gravel substrates, to rocky pools, and riffles, with the surrounding aquatic environment adhering to specific water quality standards. It is reported that its populations to show a “patchy” distribution downstream of Vanderkloof Dam, suggesting that river regulation and catchment utilization, together with the resulting constant turbidity levels, fragmented it populations in the regulated Orange River, restricting it to clearer slow flowing to stagnant water.
It is endemic to, distributed throughout the ORS, and the dominant large ORS fish species. However, its numbers decline towards the lower Orange River stretch between Aughrabies Falls and the Orange River Mouth. It is a detritivore appearing to be utilizing all aquatic habitat types in the Orange River System (ORS) from quiet, weedy backwaters to rapids. Its breeding is naturally triggered by local rains throughout summer, and spawning occurs in floodplains, main streams and rapids between mid-spring and late summer/ early autumn. Flow is a major stimulus for L. capensis’ breeding.
It is a widespread tropical African freshwater fish species. In the Orange River System, its distribution includes the Vaal River catchment, as well as the Orange River below the Orange-Vaal confluence. Its habitat preference is rapid areas. Feeds on insects and other small organisms. Used as bait for the tigerfish.
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