Sawfin (Barbus serra)
|Also known as:||Clanwilliam sawfin|
|Size||Length: up to 500 mm (2)|
|Weight||up to 7 kg (3)|
Classified as Endangered (EN) on the IUCN Red List 2007 (1).
The sawfin is a river-dwelling, South African fish with a long, pointed snout and a large first dorsal fin that is bony and serrated. Two pairs of barbels (fleshy projections) protrude from next to the relatively small mouth. Adult sawfins are deep olive-gold in colour with a light cream underside, and the head of breeding adults is covered with numerous small, pimple-like growths, or tubercles. Juvenile sawfins are silvery with irregular dark blotches (2).
Occurs only in the Olifants River system in the Western Cape Province, South Africa (2).
The sawfin inhabits rivers of clear water, with cobble beds and areas of bedrock or gravel (2). Adult sawfins prefer deep pools and mainstream channels, while juveniles are more often found in smaller tributaries (2) (3). The sawfin depends on being able to move freely between different areas of its habitat for feeding, breeding and resting (4).
The sawfin is an omnivorous fish that feeds on insects and other invertebrates as well as algae and detritus from the river bottom, leaving a trail of characteristic pockets in the sand and gravel beds as they feed (3). They are often found in large shoals, frequently in the company of the Clanwilliam yellowfish (Barbus capensis) (4).
Breeding takes place from spring (October) until early summer (December), probably in response to an increase in temperature, when sawfins congregate in deep pools below waterfalls and rapids (3).
Once widespread and abundant throughout the Olifants River system (2), recent surveys found that sawfin numbers are now dangerously low and it has disappeared entirely from parts of the main stem of the Olifants River (4). This has been caused by introduced predatory fish, primarily the smallmouth bass (Micropterus dolomieu), in addition to habitat degradation and fragmentation (2). As the Olifants River region experiences hot, dry summers, water is extracted from the main river and its tributaries to irrigate the surrounding agricultural land. Impoundments are also constructed to store water after the winter rainy season. Furthermore, river beds are bulldozed into wide channels to prevent the adjacent land from being flooded in the rainy season (2). Such activities greatly alter the habitat of the sawfin and restrict its ability to move freely between different areas.
CapeNature, a public institution responsible for biodiversity in the Western Cape (5), classifies the sawfin as endangered, which makes it an offence to remove captured fish from rivers and dams. CapeNature also undertakes regular surveys of the Olifants River system and has successfully cultured the sawfin since 1994. Juveniles are then introduced to suitable natural habitats or stocked into farm dams to establish refuge populations. Small parts of the sawfin’s range fall within protected areas, including the Cedarberg, Matjies River and Oorlogskloof Nature Reserves (2). However, to ensure the sawfin’s future it is vital to protect the habitat in the specific tributaries and the small section of the Olifants River mainstream where the sawfin remains abundant. In addition, efforts to prevent further introductions of alien predatory fish species are imperative (2).
For further information on conservation in the Western Cape Province of South Africa see:
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- Algae: simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
- Detritus: litter formed from fragments of dead material.
- Dorsal fin: the unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
- Invertebrates: animals with no backbone.
- Omnivorous: feeding on both plants and animals.
IUCN Red List (December, 2009)