Limnothrissa miodon, a clupeid endemic to Lake Tanganyika, was voluntarily introduced in Lake Kivu between 1958-1959 and enabled the development of a flourishing pelagic fishery. Recently, Lamprichthys tanganicanus, a poeciliid also endemic to Lake Tanganyika, was accidentally introduced into Lake Kivu. Because potential preys for both species are scarce in the lake, L. tanganicanus could compete with L. miodon and could constitute a threat to pelagic fisheries which rely mainly on L. miodon. The objective of this work was to study the feeding ecology of these two fish species using several methods: analysis of stomach contents, identification of dietary patterns, analysis of stable isotopes of C and N and analysis of fatty acids in fishes and in the main components of plankton. The results showed a strong diet overlap between these two fish species, indicating some level of interspecific competition. However, their differing feeding activities patterns and differing use of terrestrial, littoral and pelagic food resources could reduce this competition. Indeed, although both species occupy a similar trophic position, L. miodon is dependent much more on pelagic food resources than L. tanganicanus which has a stronger link with the littoral food web. The profiles of fatty acids in fishes and plankton components indicate that the fatty acids compositions of both species are very close, and that the nutritional quality of zooplankton varies relatively little during the year. As for the productivity of zooplankton, it undergoes significant seasonal variations, which are dependent on both quantity and composition of phytoplankton. Finally, fatty acid profiles also revealed that bacteria do contribute significantly to zooplankton and fish biomass, highlighting the contribution of the microbial food web to consumer production.
|Date of Award||30 Jun 2011|
|Supervisor||Jean-Pierre DESCY (Supervisor), Jean-Claude MICHA (Jury), Eric Depiereux (President), F. Darchambeau (Jury), Gilles Lepoint (Jury), J. Guillard (Jury) & Mwenyemali B. Kaningini (Jury)|