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  • 1
    Digitale Medien
    Digitale Medien
    The age and growth of the greenhead tilapia Oreochromis macrochir (Pisces:Cichlidae) from the Okavango Delta, Botswana (1996)
    Springer
    Hydrobiologia 321 (1996), S. 29-34 
    Details
    ISSN: 1573-5117
    Schlagwort(e): floodplain ecology ; annulus formation ; von Bertalanffy model ; Schnute model ; conservation ; management
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Sectioned otoliths were used for age and growth determination of Oreochromis macrochir, a common cichlid species from the Okavango Delta, Botswana. The Okavango Delta is a vast inland wetland ecosystem which receives annual floodwaters from the highlands of southern Angola. Floodwaters reach the northern areas of the delta between January and March and the southern areas between June and September each year. Samples were collected from sites which receive flood waters between May and August. Marginal zone analysis showed that an annulus was formed between October and December during the dry, summer period. Maximum age estimates of eleven years were obtained and growth was described by the 3 parameter von Bertalanffy model as l t = 215.24 (1−e −0.42(t+1.08)) mm SL.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00018674
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  • 2
    Digitale Medien
    Digitale Medien
    Community ecology and conservation of the fishes of the Okavango Delta, Botswana (1995)
    Springer
    Environmental biology of fishes 43 (1995), S. 109-119 
    Details
    ISSN: 1573-5133
    Schlagwort(e): Diversity ; Predictable ; Unpredictable ; Stability ; Eurytopic ; Stenotopic ; Seasonality ; Wetland ; Africa
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Synopsis The Okavango Delta is a large inland swamp in northern Botswana which receives an annual flood from the highlands of southern Angola. There are distinct fish taxocenes in the Okavango which can be separated from each other by the physical characteristics of the different habitat types with which they co-evolved. An account is given of the ecology and conservation of the fishes of the Okavango Delta. Their response to the annual flood regime, and the environmental factors that limit their distribution and abundance, are described. In the northern riverine floodplain and perennial swamp a higher species richness and ichthyomass was recorded than in the seasonal swamp and drainage rivers. Suggestions are made on the conservation of Okavango fishes taking into account the ecological characteristics of the Delta.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00002478
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  • 3
    Digitale Medien
    Digitale Medien
    The proportion of different eco-ethological sections of reproductive guilds of fishes in some African inland waters (1990)
    Springer
    Environmental biology of fishes 28 (1990), S. 179-187 
    Details
    ISSN: 1573-5133
    Schlagwort(e): Lakes ; Floodplains ; Rivers ; Perturbation ; Resilience ; Resistance ; Guarders ; Non-guarders ; Bearers ; Altricial ; Precocial ; Predictable ; Unpredictable ; Ecology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Synopsis The continent of Africa has a wide variety of inland waters ranging from rift valley lakes to endorheic and coastal lakes, floodplains and rivers. This paper makes a preliminary comparison of the number of species in different eco-ethological sections of the reproductive guild categories of non-guarders, guarders and bearers in ancient African Great Lakes (Malawi, Victoria and Tanganyika), fluctuating endorheic lakes (Ngami, Chad and Chilwa), typical rivers (Orange-Vaal, Limpopo, Phongolo, Sabi-Lundi, Middle and Lower Zambezi, Kafue, Cunene, Okavango, Niger, Luongo, Lower Zaire) and wetlands (Okavango Delta and Kafue floodplain). The results indicate that the highest percentage of bearers and guarders is found in the ancient African Great Lakes, which are characterised by relatively predictable physico-chemical regimes, whereas a higher percentage of non-guarders is found in the rivers and wetlands, which have less predictable physico-chemical regimes. The management implications of this observation are discussed, and the usefulness of the species as a unit in ecology is assessed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00751034
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  • 4
    Digitale Medien
    Digitale Medien
    The reproductive biology and early development of the African pike,Hepsetus odoe, in the Okavango Delta, Botswana (1990)
    Springer
    Environmental biology of fishes 28 (1990), S. 215-235 
    Details
    ISSN: 1573-5133
    Schlagwort(e): Spawning ; Flood ; Fecundity ; Foam nest ; Precocial ; Life-history styles ; Embryo ; Development ; Eggs
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Synopsis The reproductive biology of the African pike,Hepsetus odoe, was studied over a four-year period in the Okavango Delta, Botswana. Spawning takes place between August and May in different parts of the Delta. Fish in the seasonal swamp and drainage rivers have a truncated spawning season between August and January, while those in the perennial swamp have an extended spawning season from September to May. The variation in spawning season appears to be associated with the degree of environmental perturbation brought about by the annual flood cycle. Male and female pike mature at 140 and 160 mm standard length (SL) respectively. Females predominate in the population and produce an average of 6440 eggs per season and are multiple spawners. The number of eggs per spawning averages about 2630. The eggs are deposited in a foam nest which is guarded by the parents. Newly hatched embryos suspend themselves below the nest via a cement gland and remain in the vicinity of the spawning site until they have reached a relatively advanced stage in their development. The larval period is relatively short which implies that this species undergoes nearly a direct development. Foam nests appear to be a predator avoidance mechanism as well as an adaptation to fluctuating oxygen and water levels. The initiation of the spawning season is more closely associated with water temperature than with the annual flood cycle which appears to be more important in regulating the size of the spawning stock.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00751036
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  • 5
    Digitale Medien
    Digitale Medien
    The growth ofOreochromis andersonii (Pisces: Cichlidae) from the Okavango Delta, Botswana, and a comparison of the scale and otolith methods of ageing (1995)
    Springer
    Environmental biology of fishes 43 (1995), S. 171-178 
    Details
    ISSN: 1573-5133
    Schlagwort(e): Seasonality ; Floodplain ecology ; Ring formation ; von Bertalanffy model
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Synopsis Otoliths and scales were used for age and growth determination ofOreochromis andersonii from the Okavango Delta, Botswana. Marginal increment analysis showed that an annulus was formed in both the scales and otoliths during the dry summer period. Using scales, the growth ofO. andersonii was described by Lt = 285.27(1-e-0.26(t+2.02)) mm SL and using otoliths by the equation Lt = 267.48(1-e-0.25(t+2.18)) mm SL. Maximum age estimates of 10 years using scales and 13 years using otoliths were obtained and the growth curves were significantly different (p 〈 0.01). Age estimation using scales tended to over-emphasise growth inO. andersonii resulting in larger predicted lengths-at-age. For this reason, otoliths are considered to be more reliable and suitable than scales in determining the age and growth of this species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00002488
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