A comparative study of the life histories of the sister species, Pseudobarbus afer and Pseudobarbus asper, in the Gamtoos River system, South Africa
- Authors: Cambray, James Alfred
- Date: 1993
- Subjects: Barbus -- Life cycles , Barbus -- Ecology -- South Africa -- Gamtoos River , Cyprinidae -- Life cycles , Cyprinidae -- Ecology -- South Africa -- Gamtoos River , Minnows -- Life cycles , Minnows -- Ecology -- South Africa -- Gamtoos River
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5375 , http://hdl.handle.net/10962/d1015730
- Description: This thesis explores the biology, ecology, and life-history styles of two closely-related redfin minnows, Pseudobarbus afer and P. asper (pisces; Cyprinidae), which both occur in the Gamtoos River system of South Africa. Five of the seven species of flexible-rayed redfin minnows are in the South African Red Data Book - Fishes. This investigation was designed to provide the data which would enable conservation authorities to manage the remaining populations of the Pseudobarbus species. A thorough understanding of the Gamtoos River system was necessary to properly interpret the findings of this study. The palaeo river systems and the changing climates since the break-up of Gondwanaland are discussed so that the present day environments could be considered as well as the past environmental changes. P. afer and P. asper occur in the Gamtoos River system with no physical barrier separating the two species. P. afer only occurs in the clear mountain streams of the Cape Fold Mountain Belt whereas P. asper occurs in the highly saline and turbid Karoo section of the system. P. afer were found to be the more precocial form of the sister species. They had bigger eggs, lower relative fecundity, shorter breeding season, lower gonadosomatic indices, larger first feeding larval fish, matured later and had a longer life-span than did P. asper, which had more altricial life-history attributes. They differ in their tradeoffs with P. asper devoting more resources earlier to reproduction and having a shorter lifespan. The improvement in the one aspect of fitness (early maturity) leads to the deterioration in another, namely lifespan. Both species undertake breeding migrations to riffle areas where they spawn in mid-channel immediately above a pool after an increase in water flow. P. afer and P. asper are non-guarders of their non-adhesive eggs and young, open substrate spawners on coarse substrates (rocks) and have photophobic free embryos. The breeding season is shorter for P. afer whereas P. asper can spawn as late as April and impoundment releases can induce them to spawn. A study of comparative neuroecology revealed that of the four groups of fish analyzed (males and females of both species) male P. afer had the largest brains, especially the optic lobes and cerebellum. P. asper females had the smallest brains. No neural compensation in the external gustatory centre, the facial lobe, was found for P. asper inhabiting the turbid waters. P. afer also had significantly larger eyes and longer barbels. P. afer males were also found to have the highest density and largest nuptial tubercles as well as the most pronounced breeding colouration. It was concluded that P. asper is the more derived of the sister species pair with regard to life-history attributes. It is further suggested that investment per offspring is important in determining the life-history trajectories. Paedomorphosis has occurred and by this mechanism variability has been restored to the redfin minnows in the Groot River which enables them to survive in the highly variable, intermittent Karoo stream. The more precocial P. afer do not require this variability in the more constant and predictable environment of the Wit River.
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- Date Issued: 1993
The life history of a minnow, Barbus Anoplus, in a man-made lake in South Africa
- Authors: Cambray, James Alfred
- Date: 1982
- Subjects: Minnows -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5346 , http://hdl.handle.net/10962/d1006861
- Description: Aspects of the life history strategy of Barbus anoplus Weber were studied in a turbid man-made lake (P.K. Ie Roux impoundment, Orange River system, South Africa). The minnow has successfully colonized the shoreline of the P.K. Ie Roux impoundment, where the preferred habitats of the chubbyhead barb are flooded stream beds, erosion gullies and flooded ruderal communities. B. anoplus reaches sexual maturity in one year, at a length of about 40mm FL. They have a multiple spawning habit, with the first spawn in November or December and the second spawn in February or March. A part of the adult population undertakes a spawning migration up inflowing tributaries, while the other part breeds along the shoreline. The eggs and young develop rapidly and a proportion of the protolarvae float near the water surface, where they are probably dispersed by water currents. Most of the males die off after their second summer, whereas many females live into a third summer. Females also attain a larger maximum size (73mm FL) than males (60mm FL). The importance of increasing the reproductive potential of B. anoplus by multiple spawning is discussed. Feeding studies indicate that B. anoplus are opportunistic predators on invertebrates. The feeding habits of minnows collected from four different habitats varied. Minnows collected in the open water fed mainly on zooplankton, while shoreline populations fed on chironomid larvae and zooplankton. The most varied diet was found in fish living in a well-vegetated tributary of the impoundment which was not subject to inundation. B. anoplus is basically an r-strategist (i.e. it is small in size, shortlived, males have bright colouration, high seasonal reproductive potential). These characteristics enable the species to colonize and successfully inhabit unstable environments and probably accounts for the fact that it is the most widespread species south of the Limpopo River system. It is recommended that B. anoplus be considered as a candidate in southern Africa for further studies on life history strategies.
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- Date Issued: 1982