Other Alien Fish Projects

Alien Fish Projects


Funders: various sources including DST/NRF Centre of Excellence for Invasion Biology (CIB), NRF Incentive Funding for Rated Researchers, Joint Research Committee of Rhodes University


Ecological consequences of alien fish invasions in the Groendal Wilderness Area

Researcher: Bruce Ellender.

Freshwater ecosystems, especially upper reaches of rivers are key areas for the conservation of aquatic biodiversity because they are characterised by low species diversity, but have a high degree of endemism (Abell et al. 2007). In the Eastern Cape, South Africa, such rivers are the habitat for the IUCN red-listed species, Pseudobarbus afer (Endangered). Two of the world’s worst invasive species (Lowe et al. 2000), largemouth bass, Micropterus salmoides and smallmouth bass Micropterus dolomieu, have been introduced into the Swartkops River system. Predation by, and competition with, these alien fishes is considered the primary threat to endemic fishes (Tweddle et al. 2009). While urgent conservation action is required, the lack of current distribution data on alien and indigenous fishes severely constrains the identification and prioritisation of areas for intervention.


The aim of the proposed project is to contribute to the development of endangered fish conservation strategies in the Eastern Cape, by providing the first comprehensive assessment of the distribution and relative abundance of indigenous and alien fishes in Groendal Wilderness Area.


Biology and Ecology of largemouth bass in the Eastern Cape


Researchers: Karl Huchzermeyer, Geraldine Taylor, Kirsten Bray


The primary purpose of the research is to better understand the role that bass play in this ecosystem, what the economic impacts are and how the fishery could be better managed.  There are a number of student projects under this central theme which include studies on the age and growth, diet, and movement of this important recreational angling species.


Population dynamics of the alien Mosquitofish (Gambusia affinis) in the South African Ramsar wetland: the Wilderness lakes estuarine system


Researcher: Hans Sloterdijk


The western Mosquitofish, Gambusia affinis (Baird & Girard, 1853), Family Poeciliidae, is a native of the southern United States (Rivas, 1963). Globally, it is believed to be the most widely disseminated natural predator in the history of biological control, and as a result, the Mosquitofish is presently one of the most commonly distributed freshwater fish species around the world (Mieiro et al., 2001). In South Africa, this fish is an alien invasive species that was first introduced in 1936 for the purpose of mosquito control and as a forage fish for bass (de Moor and Bruton, 1988). Presently, populations are well established in the southern Cape (de Moor and Bruton, 1988).  In the Wilderness section of the Garden Route National Park, an estuarine lake system, little is known about the spatial and temporal distribution, biology (maturity, growth, reproductive seasonality) and the ecology (diet, population structure, relative abundance) of this fish. This is of particular concern because the presence of alien invasive fish species has been identified as a major factor affecting the biodiversity of South African freshwater fishes (Tweddle et al. 2009). Moreover, the biology and impact of this alien invasive fish in a South African estuarine environment has never been assessed.


This study aims to determine the spatial and temporal distribution of G. affinis in relation with the environmental conditions, and through their diet composition, contribute to understanding their potential impacts in the Wilderness lakes ecosystem. The findings of such a study will provide relevant information about seasonal variation in G. affinis population dynamics that result from natural processes and provide important baseline data against which the efficacy of management measures can be evaluated. As a result, this project will provide important inputs for conservation planning and management of this Ramsar and National Park site.