Straight Finned Barb (Barbus paludinosus)

THE Straight finned barb’s diagnostic features are a plain colour, strong serrated dorsal spine and straight edge to dorsal fin.
This species is normally a plain olive-grey or silver in colour, rather darker on the dorsal surface. The fins are flesh-coloured to pale yellow and specimens with a darkish line along the flanks have occasionally been recorded. Some specimens have been collected with a golden/greenish stripe running along the flank and a similar colour patch on the operculum.
The species is most likely to be confused with Barbus afrohamiltoni from which it can be most easily distinguished by a straight, rather than concave, posterior edge to the dorsal fin, and thinner caudal peduncle and overall body depth. The dorsal fin is serrated on its distal half and it has a pointed head with a small mouth and two pairs of short maxillary barbels. The species grows to a length of about 15cm.
Biology
The species occurs in most habitats but generally less abundant in dams than in rivers. In Lake Chivero it makes up about 5-10 percent (by number) of the small fish in the shallows, except at one station at the mouth of the stream where it made up to 35 percent of the population. It was not collected on the Zambezi prior to the creation of Lake Kariba and is largely absent from the lake itself. None was recorded from a sample of about 370 000 fish collected from a number of inshore site around the lake in the 1970s. The species made up 13 percent of all the fish collected during a survey of stream in the upper Manyame, being found at 28 out of 48 stations. This is probably a low proportion because exotic predators occurred at many of these stations, and others where severely polluted, although Barbus paludinosusis not as sensitive to pollution as other barbs, having being recorded — with Clarias gariepinus — at sites severely polluted by sewage effluent. Like other barbs, Barbus paludinosus is vulnerable to exotic predators and its numbers were greatly reduced when bass and nembwe were present.
It feeds on a wide range of food items. Insects, crustaceans, molluscs, fish eggs, rotifers, diatoms, blue-green algae, filamentous and non-filamentous algae and higher plants have all been recorded in its diet.
This species is potamodromous and is often seen migrating up small streams when there are floods for the first time. In the University of Zimbabwe stream, its migration pattern was similar to that of Barbus lineomacalatus, and it moved upstream with the first rains, while adults and juveniles began to move downstream from February onwards. They can have up to 2200 eggs.
Parasites and diseases
In a research it was found that most of these species were infected with larvae of the tape worm ligula intestinalis, a common parasite of cyprinid fish. There was no clear seasonal pattern of infection, although the number of infected fish seemed to be highest when the water level was low.
Economic importance
Local people harvest this species on a small scale, especially during the rains, but nowhere in Zimbabwe does it support an important fishery as it does elsewhere notably in Malawi). These barbs are known to feed voraciously on mosquito larvae and can eliminate them from sewage ponds and other similar water bodies, and must therefore be important in controlling malaria in many areas.
l Nobuhle M Sebata is a Curator of Ichthyology at the Natural History Museum