A contribution to the ecology and systematics of the genus Petrotilapia (Pisces : Cichlidae) in Lake Malawi
- Authors: Marsh, Alan Clive
- Date: 2013-03-20
- Subjects: Cichlids -- Nyasa, Lake , Petrotilapia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5355 , http://hdl.handle.net/10962/d1009513 , Cichlids -- Nyasa, Lake , Petrotilapia
- Description: The nominal species Petrotilapia tridentiger Trewavas, a rock-frequenting fish from Lake Malawi, occurs in three distinct male and female colour forms at Monkey Bay. Field observations on courtship and aggression indicate that the three colour forms are distinct species. The taxonomy of the three species of Petrotilapia that occur at Monkey Bay is revised. R. tridentiger is redescribed and two new species, P. genalutea and P. nigra, are described. The three species are very similar morphologically and are considered to be sibling species. The only morphological character which reliably separates the three sibling species is live coloration: Live coloration is considered to be an important component of the specific mate recognition systems in Petrotilapia species. The coloration of a further fourteen forms of Petrotilapia is described and it is suggested that these forms are valid species. Space resource partitioning plays an important role in facilitating the coexistence of Petrotilapia sibling species. Space is partially partitioned in terms of depth range. In shallow water, where all three species are sympatric, there are differences in the feeding sites used by the various Petrotilapia forms. Changes in niche breadth and overlap, which are associated with changes in the abundance of epilithic algae, indicate that competition for feeding space occurs between the three Petrotilapia species. The Petrotilapia species partition their resources according to a social dominance hierarchy. Dominant forms, such as territorial males, R. tridentiger females and schooling R. genalutea females, have access to rich food supplies which occur within the territories of certain highly aggressive Pseudotronheus species. are facultative and opportunistic .feeders. Petrotilapia species Speciation in allopatry is considered to be the mechanism which adequately explains the current diversity of the genus Petrotilapia. The importance of an integrative approach to future systematic and ecological research on Lake Malawi cichlids is stressed. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
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- Authors: Marsh, Alan Clive
- Date: 2013-03-20
- Subjects: Cichlids -- Nyasa, Lake , Petrotilapia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5355 , http://hdl.handle.net/10962/d1009513 , Cichlids -- Nyasa, Lake , Petrotilapia
- Description: The nominal species Petrotilapia tridentiger Trewavas, a rock-frequenting fish from Lake Malawi, occurs in three distinct male and female colour forms at Monkey Bay. Field observations on courtship and aggression indicate that the three colour forms are distinct species. The taxonomy of the three species of Petrotilapia that occur at Monkey Bay is revised. R. tridentiger is redescribed and two new species, P. genalutea and P. nigra, are described. The three species are very similar morphologically and are considered to be sibling species. The only morphological character which reliably separates the three sibling species is live coloration: Live coloration is considered to be an important component of the specific mate recognition systems in Petrotilapia species. The coloration of a further fourteen forms of Petrotilapia is described and it is suggested that these forms are valid species. Space resource partitioning plays an important role in facilitating the coexistence of Petrotilapia sibling species. Space is partially partitioned in terms of depth range. In shallow water, where all three species are sympatric, there are differences in the feeding sites used by the various Petrotilapia forms. Changes in niche breadth and overlap, which are associated with changes in the abundance of epilithic algae, indicate that competition for feeding space occurs between the three Petrotilapia species. The Petrotilapia species partition their resources according to a social dominance hierarchy. Dominant forms, such as territorial males, R. tridentiger females and schooling R. genalutea females, have access to rich food supplies which occur within the territories of certain highly aggressive Pseudotronheus species. are facultative and opportunistic .feeders. Petrotilapia species Speciation in allopatry is considered to be the mechanism which adequately explains the current diversity of the genus Petrotilapia. The importance of an integrative approach to future systematic and ecological research on Lake Malawi cichlids is stressed. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
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Age, growth and yield-per-recruit analysis of ndunduma Diplotaxodon limnothrissa (Teleostei: Cichlidae), in the southeastern arm of Lake Malawi
- Authors: Kanyerere, Geoffrey Zantute
- Date: 2004
- Subjects: Fishes -- Nyasa, Lake , Cichlids -- Nyasa, Lake , Fishes -- Growth -- Nyasa, Lake , Fishes -- Age -- Nyasa, Lake , Fishery resources -- Malawi , Fishery management -- Malawi
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5214 , http://hdl.handle.net/10962/d1005057 , Fishes -- Nyasa, Lake , Cichlids -- Nyasa, Lake , Fishes -- Growth -- Nyasa, Lake , Fishes -- Age -- Nyasa, Lake , Fishery resources -- Malawi , Fishery management -- Malawi
- Description: Diplotaxodon limnothrissa Turner (1995) is a widely distributed species occurring throughout Lake Malawi, extending from the surface to a depth of at least 220m. It is probably the most abundant cichlid in the lake with biomass estimates of around 87 000 tonnes in the pelagic zone alone. The species is exploited commercially in the southern part of the lake but since its inception the fishery has never been assessed. As such this study investigates some aspects of age and growth of the species besides applying a yield-per-recruit analysis to assess the status of the fishery. Analysis of sectioned sagittal otoliths revealed that D. limnothrissa is fast growing and relatively long-lived species, attaining ages in excess of 10 years. Growth in length was rapid in immature fish, with fish attaining almost half of their maximum size within their first year. Le ngth-at-age was described by the von Bertalanffy growth model with combined-sex growth described as Lt = 211.21(1-exp(- 0.24(t+1.36))) mm TL. Total, natural and fishing mortalities were estimated at 0.76 yr⁻¹, 0.31 yr⁻¹ and 0.45 yr⁻¹ respectively. Per-recruit analysis indicated that the D. limnothrissa stock in the southeast arm of the lake is fully exploited as indicated by the current spawner biomass-per-recruit ratios of 31-55% (SB/R)F=0. Modelling indicated that the current age-at-capture (2.67 years) is lower than the age at which yield is optimised (> 5 years) based on the F₀·₁ harvesting strategy. It is, therefore, recommended that the age-at-capture should be increased from 2.67 to 5 years to optimise yield.
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- Authors: Kanyerere, Geoffrey Zantute
- Date: 2004
- Subjects: Fishes -- Nyasa, Lake , Cichlids -- Nyasa, Lake , Fishes -- Growth -- Nyasa, Lake , Fishes -- Age -- Nyasa, Lake , Fishery resources -- Malawi , Fishery management -- Malawi
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5214 , http://hdl.handle.net/10962/d1005057 , Fishes -- Nyasa, Lake , Cichlids -- Nyasa, Lake , Fishes -- Growth -- Nyasa, Lake , Fishes -- Age -- Nyasa, Lake , Fishery resources -- Malawi , Fishery management -- Malawi
- Description: Diplotaxodon limnothrissa Turner (1995) is a widely distributed species occurring throughout Lake Malawi, extending from the surface to a depth of at least 220m. It is probably the most abundant cichlid in the lake with biomass estimates of around 87 000 tonnes in the pelagic zone alone. The species is exploited commercially in the southern part of the lake but since its inception the fishery has never been assessed. As such this study investigates some aspects of age and growth of the species besides applying a yield-per-recruit analysis to assess the status of the fishery. Analysis of sectioned sagittal otoliths revealed that D. limnothrissa is fast growing and relatively long-lived species, attaining ages in excess of 10 years. Growth in length was rapid in immature fish, with fish attaining almost half of their maximum size within their first year. Le ngth-at-age was described by the von Bertalanffy growth model with combined-sex growth described as Lt = 211.21(1-exp(- 0.24(t+1.36))) mm TL. Total, natural and fishing mortalities were estimated at 0.76 yr⁻¹, 0.31 yr⁻¹ and 0.45 yr⁻¹ respectively. Per-recruit analysis indicated that the D. limnothrissa stock in the southeast arm of the lake is fully exploited as indicated by the current spawner biomass-per-recruit ratios of 31-55% (SB/R)F=0. Modelling indicated that the current age-at-capture (2.67 years) is lower than the age at which yield is optimised (> 5 years) based on the F₀·₁ harvesting strategy. It is, therefore, recommended that the age-at-capture should be increased from 2.67 to 5 years to optimise yield.
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Ecological interaction between the introduced and native rock-dwelling cichlid fishes of Lake Malawi National Park, Malawi
- Authors: Munthali, Simon Muchina
- Date: 1997
- Subjects: Cichlids -- Nyasa, Lake
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5266 , http://hdl.handle.net/10962/d1005110
- Description: More than twenty years ago, over twenty species of the rock-dwelling cichlid species (Mbuna) were translocated from the northern Lake Malawi, where they are endemic, to Thumbi West Island, Lake Malawi National Park, in the southern part of Lake Malawi. Among these species, Cynotilapia afra, Pseudotropheus callainos and Pseudotropheus tropheops 'red cheek' are strongly territorial, and have increased substantially in number and are widely distributed, particularly in the three to seven metre depth band of the rocky habitats at the Island of Thumbi West. It is feared that the increase in population density of translocated species (hereafter referred to as introduced species) may be at the expense of ecologically equivalent native species which could be eliminated. In this thesis the following key hypotheses have been tested: (i) that the introduced species having originated from a region of Lake Malawi which is generally poor in nutrients and introduced in an area which is richer in nutrients, would cope better than the native species during periods of nutrient scarcity which occur frequently, often seasonally in oligotrophic lakes, such as Lake Malawi; (ii) that the introduced species are fitter than their ecologically equivalent native species in the acquisition of territorial space in which they breed, feed and seek shelter, and (iii) that introduced and native species coexist by utilizing different microhabitats. Results show that: 1. the introduced species, P. callainos and P. tropheops 'red cheek' may have responded positively to enhanced nutrient availability, as they were found to have better condition factors and fecundity indices at Thumbi West Island than at sites of their origin, in the northern lake Malawi. Cynotilapia afra, P. callainos and P. tropheops 'red cheek' also maximise their life-span fecundity by starting to reproduce at relatively smaller size than the native species with which they overlap in microhabitat requirements. Similarly, their breeding peaks precede the breeding peaks of the native species with which they overlap in microhabitat requirements. Consequently, due to priority residence effects, the offspring of introduced species may have a competitive edge in the use of essential resources, e.g., refuge over the offspring of the native species whose peak-recruitment occurs later in the year. 2. There is an overlap between the introduced and native species in their microhabitat requirements. Consequently, interference competition between them for territorial sites occurs. The choice of optimal territory sites is constrained by the fact that females preferentially mate with males that defend significantly smaller holes, or crevices among the rocks, probably as a means of minimizing egg predation during spawning. 3. The population of territorial males of introduced species seems to grow exponentially, depending on the availability of suitable microhabitats, and an equilibrium between them and males of the native species may be reached. Competition for optimal territory sites seems to intensify, once the carrying capacity in a particular area has been reached, and it is at this stage that some territorial males of the introduced and native species with similar microhabitat requirements, e.g., C. afra and P. zebra, or P. tropheops 'red cheek' and its sibling native species, P. tropheops 'orange chest' displace each other. However, it seems unlikely that any of the native species which were compared with the introduced species would be driven to extinction because: (a) there is a considerable interspecific territory turn-over between the introduced and native species that overlap in microhabitat requirements. (b) Even in situations where some of the native species occur in microhabitats that are not of their preference, they occupy patches of suitable sites and are capable of breeding. (c) It has been suggested that since introduced and native species breed throughout the year and are polygamous and have intraspecifically shared paternity, they are capable of fertilizing many gravid females of their own species. Therefore, the population of native species may not be detrimentally limited by the presence of introduced species. (d) The introduced and native Mbuna species that prefer small rocks coexist in the same microhabitats, partly by feeding at different sites with different intensity and they also feed at different heights in the water column. 4. The following studies have been recommended before any management intervention, such as culling is adopted: (i). interaction between the introduced and native species in the shallow and deep rocky habitats; (ii) space utilization and survivorship of juveniles of the introduced and native species; (iii) laboratory studies to confirm the role of different nutrient regimes on the fecundity of Mbuna; (iv) the possibility of hybridization between the introduced and native species; (v) monitoring of population growth and distribution of the introduced species around Thumbi West Island should continue in order to detect their long-term effects on the native species.
- Full Text:
- Authors: Munthali, Simon Muchina
- Date: 1997
- Subjects: Cichlids -- Nyasa, Lake
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5266 , http://hdl.handle.net/10962/d1005110
- Description: More than twenty years ago, over twenty species of the rock-dwelling cichlid species (Mbuna) were translocated from the northern Lake Malawi, where they are endemic, to Thumbi West Island, Lake Malawi National Park, in the southern part of Lake Malawi. Among these species, Cynotilapia afra, Pseudotropheus callainos and Pseudotropheus tropheops 'red cheek' are strongly territorial, and have increased substantially in number and are widely distributed, particularly in the three to seven metre depth band of the rocky habitats at the Island of Thumbi West. It is feared that the increase in population density of translocated species (hereafter referred to as introduced species) may be at the expense of ecologically equivalent native species which could be eliminated. In this thesis the following key hypotheses have been tested: (i) that the introduced species having originated from a region of Lake Malawi which is generally poor in nutrients and introduced in an area which is richer in nutrients, would cope better than the native species during periods of nutrient scarcity which occur frequently, often seasonally in oligotrophic lakes, such as Lake Malawi; (ii) that the introduced species are fitter than their ecologically equivalent native species in the acquisition of territorial space in which they breed, feed and seek shelter, and (iii) that introduced and native species coexist by utilizing different microhabitats. Results show that: 1. the introduced species, P. callainos and P. tropheops 'red cheek' may have responded positively to enhanced nutrient availability, as they were found to have better condition factors and fecundity indices at Thumbi West Island than at sites of their origin, in the northern lake Malawi. Cynotilapia afra, P. callainos and P. tropheops 'red cheek' also maximise their life-span fecundity by starting to reproduce at relatively smaller size than the native species with which they overlap in microhabitat requirements. Similarly, their breeding peaks precede the breeding peaks of the native species with which they overlap in microhabitat requirements. Consequently, due to priority residence effects, the offspring of introduced species may have a competitive edge in the use of essential resources, e.g., refuge over the offspring of the native species whose peak-recruitment occurs later in the year. 2. There is an overlap between the introduced and native species in their microhabitat requirements. Consequently, interference competition between them for territorial sites occurs. The choice of optimal territory sites is constrained by the fact that females preferentially mate with males that defend significantly smaller holes, or crevices among the rocks, probably as a means of minimizing egg predation during spawning. 3. The population of territorial males of introduced species seems to grow exponentially, depending on the availability of suitable microhabitats, and an equilibrium between them and males of the native species may be reached. Competition for optimal territory sites seems to intensify, once the carrying capacity in a particular area has been reached, and it is at this stage that some territorial males of the introduced and native species with similar microhabitat requirements, e.g., C. afra and P. zebra, or P. tropheops 'red cheek' and its sibling native species, P. tropheops 'orange chest' displace each other. However, it seems unlikely that any of the native species which were compared with the introduced species would be driven to extinction because: (a) there is a considerable interspecific territory turn-over between the introduced and native species that overlap in microhabitat requirements. (b) Even in situations where some of the native species occur in microhabitats that are not of their preference, they occupy patches of suitable sites and are capable of breeding. (c) It has been suggested that since introduced and native species breed throughout the year and are polygamous and have intraspecifically shared paternity, they are capable of fertilizing many gravid females of their own species. Therefore, the population of native species may not be detrimentally limited by the presence of introduced species. (d) The introduced and native Mbuna species that prefer small rocks coexist in the same microhabitats, partly by feeding at different sites with different intensity and they also feed at different heights in the water column. 4. The following studies have been recommended before any management intervention, such as culling is adopted: (i). interaction between the introduced and native species in the shallow and deep rocky habitats; (ii) space utilization and survivorship of juveniles of the introduced and native species; (iii) laboratory studies to confirm the role of different nutrient regimes on the fecundity of Mbuna; (iv) the possibility of hybridization between the introduced and native species; (v) monitoring of population growth and distribution of the introduced species around Thumbi West Island should continue in order to detect their long-term effects on the native species.
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An ecological study of territoriality in four Cichlid species resident on rocky shores near Monkey Bay, Lake Malawi
- Authors: Sharp, Bradley John
- Date: 1982
- Subjects: Cichlids -- Nyasa, Lake , Cichlids -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5340 , http://hdl.handle.net/10962/d1005927 , Cichlids -- Nyasa, Lake , Cichlids -- Behavior
- Description: This study centres on a diverse assemblage of epilithic algal grazing fish (17 cichlids and 2 cyprinids) found on the rocky shores near Monkey Bay, Lake Malawi. Diet overlap among these species is large, but competitive exclusion is apparently avoided by the species having different feeding structures, behaviour and distribution on the shore. In many respects the ecology and behaviour of the cichlid fishes inhabiting the rocky zones of Lake Malawi parallel those of coral reef fish. In both communities there are species which are highly territorial, resulting in resource subdivision and, in some cases, the development of algal gardens. As this behaviour has not been previously reported for cichlid species, this thesis describes the territoriality of the rock-dwelling cichlids of Monkey Bay, Lake Malawi, and poses three specific questions: 1. What is the function of territoriality? 2. How do the territorial species subdivide the space resource? 3. What prevents one species taking over all the available space? It is suggested that interspecific territoriality evolved in response to a shortage of food, and, at present, serves principally to defend an algal garden i.e. a food supply of high standing crop. The species studied are extremely site specific. The rocky shore is subdivided among the four species according to the rock configuration, size, algal mat composition and position on the shore, of the available sites. An experimental study of the space utilization of the two common territorial species, referred to as 'Pseudotropheus orange cheek' and 'Pseudotropheus aggressive', showed that suitable territory sites are in short supply and that these species are in competition for some sites. These results do not support those of Fryer (1959) who suggested that a superabundance of food enabled fish to coexist by sharing the same food resource. Indeed it now appears that a shortage of food may have been a major driving force during the recent evolution of the species studied.
- Full Text:
- Authors: Sharp, Bradley John
- Date: 1982
- Subjects: Cichlids -- Nyasa, Lake , Cichlids -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5340 , http://hdl.handle.net/10962/d1005927 , Cichlids -- Nyasa, Lake , Cichlids -- Behavior
- Description: This study centres on a diverse assemblage of epilithic algal grazing fish (17 cichlids and 2 cyprinids) found on the rocky shores near Monkey Bay, Lake Malawi. Diet overlap among these species is large, but competitive exclusion is apparently avoided by the species having different feeding structures, behaviour and distribution on the shore. In many respects the ecology and behaviour of the cichlid fishes inhabiting the rocky zones of Lake Malawi parallel those of coral reef fish. In both communities there are species which are highly territorial, resulting in resource subdivision and, in some cases, the development of algal gardens. As this behaviour has not been previously reported for cichlid species, this thesis describes the territoriality of the rock-dwelling cichlids of Monkey Bay, Lake Malawi, and poses three specific questions: 1. What is the function of territoriality? 2. How do the territorial species subdivide the space resource? 3. What prevents one species taking over all the available space? It is suggested that interspecific territoriality evolved in response to a shortage of food, and, at present, serves principally to defend an algal garden i.e. a food supply of high standing crop. The species studied are extremely site specific. The rocky shore is subdivided among the four species according to the rock configuration, size, algal mat composition and position on the shore, of the available sites. An experimental study of the space utilization of the two common territorial species, referred to as 'Pseudotropheus orange cheek' and 'Pseudotropheus aggressive', showed that suitable territory sites are in short supply and that these species are in competition for some sites. These results do not support those of Fryer (1959) who suggested that a superabundance of food enabled fish to coexist by sharing the same food resource. Indeed it now appears that a shortage of food may have been a major driving force during the recent evolution of the species studied.
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