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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.
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