The ecology of the Guinean tilapia Tilapia guineensis a dominant species of the lower Gambia Rive... more The ecology of the Guinean tilapia Tilapia guineensis a dominant species of the lower Gambia River floodplains and an important food source in parts of West Africa was studied to better understand the threat posed from construction of a barrage across the river. The catch per unit effort (CPUE) of T. guineensis was positively associated with conductivity and dissolved oxygen and negatively associated with water depth and the % vegetation cover. Diet studies indicated that the T. guineensis is primarily an iliophage. The peak of reproduction was at the beginning of the rainy season. CPUE peaked in May, just before the first rains, and subsequently declined, probably reflecting movement into newly flooded habitat. Median size at maturity was 11.6 cm total length, L(T), for females and 12.5 cm L(T) for males. L(T)-frequency analysis indicated several juvenile cohorts as well as very young fish on the floodplains each month, suggesting continuation of reproduction throughout the rainy season. The impending construction of a hydroelectric dam on the Gambia River is likely to affect T. guineensis negatively through anticipated changes in the hydrology of the river.
Freshwater stingrays from Thailand Himantura chaophraya and H. cf. H. signifer show high total ta... more Freshwater stingrays from Thailand Himantura chaophraya and H. cf. H. signifer show high total tail spine serration count, close to what can be found in marine species. It seems therefore that total tail spine serration cannot be used to infer stingray habitat.
Thesis (M.Sc.)--Chulalongkorn University, 1999 Rainboth (1996b) has varified all Puntius species ... more Thesis (M.Sc.)--Chulalongkorn University, 1999 Rainboth (1996b) has varified all Puntius species of Smith (1945) into 4 genera, Puntius, Systomus, Barbodes and Hypsibarbus by taking their distinctive external morphological differences into account. Since cytotaxonomy by the studying of karyotypes and distributions of nucleolus organizer regions (NORs) might provide possible useful data to support such taxonomic problem or vice versa. This study was therefore designed to do comparative study by examining some external morphological features but emphasizing on the comparison of karyotypes and distributions of NORs of a representative cyprinid species of those above 4 genera, they are Puntius brevis, Systomus orphoides, Barbodes gonionotus and Hypsibarbus wetmorei, respectively. The fish materials in this study were obtained from middle plain of the Chao Phraya river system. Each species was taken at the place as many as enough for selection. For morphometric and meristic studies ten s...
Grouping provides many potential benefits to individuals in terms of foraging and anti-predator p... more Grouping provides many potential benefits to individuals in terms of foraging and anti-predator protection. However, it has been suggested that individuals could gain additional benefits in terms of indirect fitness by grouping with kin. Surprisingly, the genetic composition of wild fish shoals and the importance of kin-associated shoaling remain poorly understood. The Trinidadian guppy (Poecilia reticulata) has life history traits that might promote kin structure of shoals such as internal fertilisation and small brood size in contrast to many other fish species. Even though previous studies did not find any indication of kin structure in shoals of adult guppies, it is possible that related juveniles remain together in shoals, partly because of lower mobility and because the advantages of kin association may change with age. Using 10 microsatellite markers, we conducted a genetic analysis on 40 shoals from four populations. Pair-wise relatedness was inferred using a modified versio...
Abstract Group living is the result of a dynamic trade-off between associated costs and benefits.... more Abstract Group living is the result of a dynamic trade-off between associated costs and benefits. However, these costs and benefits are not necessarily distributed equally across different spatial positions of groups which may result in different fitness returns for individuals occupying different positions in groups. Here we consider whether leadership of a group during a navigation task in humans may have a specific cost associated with it. Pairs of students performed a counting task whilst walking through two obstacle courses, once ...
Reciprocal altruism has been proposed as a possible mechanism for the evolution of cooperative be... more Reciprocal altruism has been proposed as a possible mechanism for the evolution of cooperative behaviour. However, very few investigations have tested predictions of reciprocity in wild animal populations. In the current investigation we simulated defection during predator inspection in a wild population of guppies, Poecilia reticulata. Two experiments were run: the first simulating defection during a single exposure to a predator and the second during multiple exposures to a predator. We then compared subsequent ...
The ecology of the Guinean tilapia Tilapia guineensis a dominant species of the lower Gambia Rive... more The ecology of the Guinean tilapia Tilapia guineensis a dominant species of the lower Gambia River floodplains and an important food source in parts of West Africa was studied to better understand the threat posed from construction of a barrage across the river. The catch per unit effort (CPUE) of T. guineensis was positively associated with conductivity and dissolved oxygen and negatively associated with water depth and the % vegetation cover. Diet studies indicated that the T. guineensis is primarily an iliophage. The peak of reproduction was at the beginning of the rainy season. CPUE peaked in May, just before the first rains, and subsequently declined, probably reflecting movement into newly flooded habitat. Median size at maturity was 11.6 cm total length, L(T), for females and 12.5 cm L(T) for males. L(T)-frequency analysis indicated several juvenile cohorts as well as very young fish on the floodplains each month, suggesting continuation of reproduction throughout the rainy season. The impending construction of a hydroelectric dam on the Gambia River is likely to affect T. guineensis negatively through anticipated changes in the hydrology of the river.
Freshwater stingrays from Thailand Himantura chaophraya and H. cf. H. signifer show high total ta... more Freshwater stingrays from Thailand Himantura chaophraya and H. cf. H. signifer show high total tail spine serration count, close to what can be found in marine species. It seems therefore that total tail spine serration cannot be used to infer stingray habitat.
Thesis (M.Sc.)--Chulalongkorn University, 1999 Rainboth (1996b) has varified all Puntius species ... more Thesis (M.Sc.)--Chulalongkorn University, 1999 Rainboth (1996b) has varified all Puntius species of Smith (1945) into 4 genera, Puntius, Systomus, Barbodes and Hypsibarbus by taking their distinctive external morphological differences into account. Since cytotaxonomy by the studying of karyotypes and distributions of nucleolus organizer regions (NORs) might provide possible useful data to support such taxonomic problem or vice versa. This study was therefore designed to do comparative study by examining some external morphological features but emphasizing on the comparison of karyotypes and distributions of NORs of a representative cyprinid species of those above 4 genera, they are Puntius brevis, Systomus orphoides, Barbodes gonionotus and Hypsibarbus wetmorei, respectively. The fish materials in this study were obtained from middle plain of the Chao Phraya river system. Each species was taken at the place as many as enough for selection. For morphometric and meristic studies ten s...
Grouping provides many potential benefits to individuals in terms of foraging and anti-predator p... more Grouping provides many potential benefits to individuals in terms of foraging and anti-predator protection. However, it has been suggested that individuals could gain additional benefits in terms of indirect fitness by grouping with kin. Surprisingly, the genetic composition of wild fish shoals and the importance of kin-associated shoaling remain poorly understood. The Trinidadian guppy (Poecilia reticulata) has life history traits that might promote kin structure of shoals such as internal fertilisation and small brood size in contrast to many other fish species. Even though previous studies did not find any indication of kin structure in shoals of adult guppies, it is possible that related juveniles remain together in shoals, partly because of lower mobility and because the advantages of kin association may change with age. Using 10 microsatellite markers, we conducted a genetic analysis on 40 shoals from four populations. Pair-wise relatedness was inferred using a modified versio...
Abstract Group living is the result of a dynamic trade-off between associated costs and benefits.... more Abstract Group living is the result of a dynamic trade-off between associated costs and benefits. However, these costs and benefits are not necessarily distributed equally across different spatial positions of groups which may result in different fitness returns for individuals occupying different positions in groups. Here we consider whether leadership of a group during a navigation task in humans may have a specific cost associated with it. Pairs of students performed a counting task whilst walking through two obstacle courses, once ...
Reciprocal altruism has been proposed as a possible mechanism for the evolution of cooperative be... more Reciprocal altruism has been proposed as a possible mechanism for the evolution of cooperative behaviour. However, very few investigations have tested predictions of reciprocity in wild animal populations. In the current investigation we simulated defection during predator inspection in a wild population of guppies, Poecilia reticulata. Two experiments were run: the first simulating defection during a single exposure to a predator and the second during multiple exposures to a predator. We then compared subsequent ...
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