The purpose of the study was to assess the effect of introducing non-native fish species (Limnothrissa miodon, Oreochromis niloticus and Cherax quadricarinatus) have on ecosystem services of the Lake Kariba fishery. Three hundred and seventy-seven (377) respondents were picked randomly from the 3 strata (I, II and IV) of the lake and were interviewed using a questionnaire. Focus Group Discussion (FGD) and interviews with headmen/women, experts, government leaders and processors/exporters were also done to strengthen and validate the results. Analysis of data was done by cross-tabulation using chi-square analysis using SPSS version 16. Microsoft Excel was used to produce outputs, which was done based on defined themes. Responses from FGD and key informants were analyzed using classical content analysis. The study revealed that although there has been an ecological impact on the Lake Kariba fishery, introduced non-native species have had a positive effect on ecosystem services through improved peoples’ livelihoods brought about by improved household food security, improved nutrition, employment creation and overall contribution to the Gross Domestic Product (GDP) of the country. Around 59.42% of the respondents showed an affirmative response that introduced non-native fish species have a positive response on their lives. It’s therefore concluded that despite the ecological effects, introduced species have a positive effect on livelihoods through improved food security, employment creation, income generation and overall contribution to Zambia’s GDP. Keywords: Non-native species, Ecosystem services, Oreochromis niloticus, Limnothrissa miodon, Cherax quadricarinatus, Ecosystem, Lake Kariba.

Patterns of intra- and interspecific variation based on environmental conditions in which populations live may reflect adaptive responses to their habitat. This is particularly relevant in a lake habitat where closely related species occur sympatrically. This study was aimed at determining consistency in morphological traits in head and body shapes in two haplochromine species (Haplochromis insidiae and Haplochromis kamiranzovu) in littoral and/ pelagic zones and to estimate the extent to which the habitats affect variations between the species. Specimens of both species were taken from littoral and pelagic zones, in the northern and southern parts of Lake Kivu. Morphometrics and landmark-characteristics were recorded and compared within and between habitats. The results showed that differences were found among the two species, among the two zones and for both. The most prominent difference was in the head; including the relative size of the jaws, head length and position of the pectoral fin insertion. Variation in head morphology is normally related to feeding. Changes in body shape can be linked to differences in environment and food availability between the two habitats which could have enabled the species to co-exist. This capacity is important in lakes like Kivu which have low habitat diversity compared to other African Great lakes like Malawi, Tanganyika and Victoria and provide some explanation in the differences in the number of haplochromine species in these lakes. The genetic basis of these phenotypic changes should be examined in future research.

Evaluating the feeding interaction of fishes is fundamental in understanding the impacts of introduced species on the community structure and ecosystem function of native species. In the Zambian Rivers, studies have shown that native species has been impacted upon by exotic Oreochromis niloticus, but few studies have investigated feeding interactions between exotic Oreochromis niloticus which is omnivorous and aquaculture preferred herbivorous native species (Coptodon rendalli) in the natural distribution. We analysed the stomach contents of 368 specimens of the fishes to examine the feeding interactions between O. niloticus and C. rendalli in the upper Kabompo River, northwest of Zambia. Both species were grouped into size classes of <50, 51−100 and 101−150 mm total length (TL). However, in the size classes 51-100 mm and 151-100 mm O. niloticus had a larger dietary niche because of its generalist diet than the native species, whose diet mainly comprised of diatoms and algae. There was no significant ontogenetic diet shift for both species, except for O. niloticus in size class 101-150 mm, whose diet consisted mainly of zooplanktons and micro fauna. The results showed an interspecific competition in their size classes, except for 101-150 mm size class, that indicated low dietary overlap. This poses major impacts on food web structure and may explain population decreases of some native species in the upper Kabompo River. Future studies are required to further understand feeding interaction between the exotic and other native fishes in the Kabompo River and other rivers across African where the species coexist.

Investigating the determinants of reproductive biology of fishes is an essential component of biological research. Breeding pattern was investigated to determine the impact of exotic Oreochromis niloticus on the native congeneric Oreochromis macrochir in the upper Kabompo River. Gonado-somatic index and sex ratio was used to investigate the breeding pattern in both invaded (where O. niloticus is present) and uninvaded (where O. niloticus is absent) sections of the river. Oreochromis macrochir was the only native congeneric species found in both sections. Results showed that the overall gonado-somatic index means for both sexes of O. macrochir in both sections were similar. For O. niloticus in invaded section indicated all year reproduction though reduced spawning in cold season (May-June), but with increased spawning activity in wet season (February-March). In O. macrochir, males and females were found breeding in both dry and wet seasons only, as for cold season no reproduction was recorded. Sex ratio (females: males) was 1:1.3 and 1:1.7 for O. niloticus and O. macrochir respectively, and both significantly deviated from the sex ratio of 1:1 (ꭓ2=8.42 and 9.37; p<0.05). Oreochromis niloticus formed the most abundant fish caught 221(63.5%) than O. macrochir 127(36.5%). Our study has revealed that O. niloticus was able to spawn in all seasons with 23% higher breeding population than O. macrochir, which explains the suppression in the abundance. We expect O. niloticus to invade further downstream of the Kabompo River due to natural dispersion.