Investigating the determinants of reproductive biology of fishes is an essential component of fisheries research. Breeding patterns were investigated to determine the impact of exotic Oreochromis niloticus on the native congeneric Oreochromis macrochir in the upper Kabompo River in the northwest part of Zambia. Gonado-somatic index and sex ratio was used to investigate the breeding patterns in both invaded (where O. niloticus is present) and uninvaded (where O. niloticus is absent) sections of the river. 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 through reduced spawning in May-June, but with increased spawning activity in February-March. In O. macrochir, males and females were found breeding in both December and February-March months, as for the month of June 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 (?2=8.42 and 9.37; p<0.05). Oreochromis niloticus was 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 across all sampled months with 23% higher breeding population than O. macrochir, might explains the suppression in the abundance of native O. macrochir. Due to the superior breeding patterns of O. niloticus, fisheries and wildlife and aquaculture practitioners need to make contingency plans to either alleviate its effects or harness its benefits even further downstream of the Kabompo River.