Common names: Clanwilliam yellowfish (E), Clanwilliam geelvis (Afrikaans).

Conservation status: Rare (South African Red Data Book -Fishes, Skelton 1987)

Identification: D IV + 9, A III + 5, LL 40-45, 16-20 scales around the caudal peduncle. The primary dorsal fin ray is flexible and segmented, originates above or slightly in front of origin of pelvics. The mouth with variable lips and 2 pairs of barbels. Ripe males are golden and the juveniles are silvery with dark blotches. Reaches 987 mm TL (10.66 kg). Drawing by Penny Meakin.

Distribution: Endemic to sections of the Olifants River system in the Western Cape (31 30' to 33 S; 18 30' to 19 30'E). Abundance: Dwindling numbers are due to the introduction of alien predators, poor land management and construction of main channel dams restricting migrations.

Habitat and ecology: The eggs and free embryos are riffle dwellers. The eggs are non-adhesive and fall between the cobbles and gravel of the spawning bed. Free embryos are photophobic and remain in the same habitat as the eggs for 10-12 days (at 22 C); at swim-up the free embryos are carried downstream to shallow, placid, sandy areas where they commence feeding as larvae. Larvae and early juveniles are edge dwellers. Older juveniles inhabit pools, sheltered backwaters and shallow, marginal areas of the mainstream (Skelton 1987), but can also be active in the main channel of tributaries, where they maintain position in the gentle summer flows (personal observation). Adults are pool dwellers most often found in clear, rocky pools, or deeper reaches, often with strong flow. The yellowfish is an omnivore with a diet of algae, aquatic invertebrates and larger fish will eat small fish and frogs.

Reproduction: Barbus capensis is a multiple spawning species per season and within each spawning period lasting a day or two it can be a repeat spawner (Cambray et al. 1997). The females are large powerful swimmers able to maintain their position over the mid-channel cobble/gravel spawning beds for hours. Males dart out from cover, align with the female, vibrate, spawn and then return to cover. Barbus capensis belongs in the following reproductive style as defined by Balon (1975): ethological section of non-guarders, open substratum spawners (A.1) and the guild lithophils (A.1.3.) Which are rock and gravel spawners with benthic free embryos. Barbus capensis spreads its reproductive effort over the dry season and spawning cues may be any increased flows (Cambray et al. 1997).

Threats: The species is threatened by invasive alien fish, loss of habitat due to water abstraction and damming. Main channel dam walls have fragmented the stocks and have reduced the length of the possible spawning migrations and mixing of populations.

Conservation action: There is a hatchery for this species near the Clanwilliam Dam wall. It is unfortunate that some of the hatchery bred B. capensis have been moved beyond their natural range in the system and will therefore impact on the smaller threatened species in this river system. Properly managed water releases from Clanwilliam Dam can be used to trigger spawning and lead to higher recruitment levels. Extension of the limited spawning beds in this area might be beneficial combined with removal of alien fish predators. There should be a conservation education programme initiated to reach those living in and around the Olifants catchment.

Conservation recommendations: Further research is required on the spawning requirements of the species and the tolerance of this species to increasing salinity and eutrophication levels. Knowing that the fish are repeat as well as multiple spawners is important in recommending suitable 'artificial spawning trigger floods' and their frequency and timing below the Clanwilliam Dam wall (Cambray et al. 1997).

Remarks: This once formerly abundant species was known as one of the best freshwater angling species in the world. It is ironic that the introduction of a much smaller, more common alien angling species into the Olifants River system, Micropterus dolomieu, is now one of the main negative impacts on the remaining B. capensis populations! The Olifants River is a hotspot of endemic fish species richness (Skelton et al. 1995) and as such requires an urgent catchment management plan.

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Balon, E.K. 1975. Reproductive guilds of fishes: a proposal and definition. J. Fish. Res. Bd Can. 32: 821-864.

Cambray, J.A., J.M. King, & C. Bruwer. 1997. Spawning behaviour and early development of the Clanwilliam yellowfish (Barbus capensis; Cyprinidae), linked to experimental dam releases in the Olifants River, South Africa. Regul. Rivers 13(6): 579-602.

Skelton, P.H. 1987. South African Red Data Book - Fishes. S. Afr. Nat. Sci. Prog. Rep. no. 137. 199 pp.