Breeding pattern of Oreochromis niloticus (Linnaeus, 1758) (Pisces: Cichlidae) versus native congeneric species, Oreochromis macrochir (Boulinger, 1912) in the upper Kabompo River, northwest of Zambia

Abstract

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.

Epidemiology of epizootic ulcerative syndrome (EUS) in fish in the main water bodies of the Kavango–Zambezi and Great Limpopo transfrontier conservation areas of Zimbabwe

“…The African sharptooth catfish was found to be the most widely distributed and this finding supports earlier observations of it being the most widely distributed fish species in Africa and it thrives in polluted water bodies (Skelton, 2001). Similar to the African sharptooth catfish, the Nile tilapia which is considered to be non‐native in most water bodies (Jere et al, 2021) was also noted to be widely distributed. Studies elsewhere indicated that the Nile tilapia has tended to dominate other species due to its aggressive ability to migrate and thrive in disturbed water habitats and its year‐round breeding patterns (Jere et al, 2021).…”

“…Similar to the African sharptooth catfish, the Nile tilapia which is considered to be non‐native in most water bodies (Jere et al, 2021) was also noted to be widely distributed. Studies elsewhere indicated that the Nile tilapia has tended to dominate other species due to its aggressive ability to migrate and thrive in disturbed water habitats and its year‐round breeding patterns (Jere et al, 2021). The biological behaviour of the Nile tilapia could partly explain why this species was caught even in the aquaculture facilities that are not monocultures.…”